| Seq | Timestamp | Type | Name | Duration |
|---|---|---|---|---|
| 0/0 | 2026/09/24 01:07 | flow | patch-triage |
2mArgs:null Results: {
"EnableConfigs": [
"NETFS_SUPPORT",
"CIFS",
"9P_FS",
"NET_9P"
],
"FocusSymbols": [
"netfs_clear_stale_post_eof",
"netfs_buffered_write_iter_locked",
"netfs_unbuffered_write_iter",
"cifs_setsize",
"cifs_remap_file_range",
"cifs_file_copychunk_range",
"smb3_zero_range"
],
"KMSANReasoning": "The patch introduces `netfs_clear_stale_post_eof()` to zero out stale pagecache data in the post-EOF region when a file is extended, preventing dirty data written via mmap beyond the previous EOF from being exposed as file content. It also adjusts truncation and invalidation ranges in CIFS.\n\n- No uninitialized stack or heap allocations/structures are introduced or modified. All local variables (`mapping`, `fgp`, `folio`, `offset`, `end`) are fully initialized scalars.\n- No uninitialized kernel memory or struct padding is copied to user space. The data cleared in the pagecache is previously written user data (or page content) to satisfy POSIX hole-zeroing semantics, not uninitialized kernel memory.\n- Any potential bugs introduced by these changes (e.g., potential out-of-bounds indexing in `folio_zero_segment()`, locking/sleeping issues under `FGP_LOCK` or `IOCB_NOWAIT`, or NULL/ERR pointer dereferences on `folio`) are covered by standard sanitizers like KASAN and LOCKDEP.\n- There are no uninitialized memory risks that would require or benefit from a dedicated KMSAN fuzzing session.",
"NeedsKMSAN": false,
"Reasoning": "The patch series modifies core netfs and CIFS pagecache handling when extending files or operating on file ranges. It introduces `netfs_clear_stale_post_eof()` to clear and clean stale post-EOF pagecache folios dirtied via mmap before extending a file, and integrates it into netfs buffered/unbuffered write paths and CIFS setsize/range operations. These are reachable file operations in virtualized environments (e.g. via 9p or CIFS/SMB loopback) involving folio locking, clean/dirty state transitions, and pagecache truncation, warranting fuzzing.",
"WorthFuzzing": true
} |
| 1/1 | 2026/09/24 01:07 | action | read-patch-diff |
0mArgs:null Results: {
"PatchDiff": "commit ffe5c0db81fb5e586f5ad7fe7cabab11275ed0d4\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Thu Sep 24 01:07:46 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/Documentation/filesystems/netfs_library.rst b/Documentation/filesystems/netfs_library.rst\nindex ddd799df6ce36..58b0adacc2f3e 100644\n--- a/Documentation/filesystems/netfs_library.rst\n+++ b/Documentation/filesystems/netfs_library.rst\n@@ -451,6 +451,24 @@ one.\n The inode should be marked ``NETFS_ICTX_SINGLE_NO_UPLOAD`` if this API is to be\n used. The writeback function requires the buffer to be of ITER_FOLIOQ type.\n \n+Clearing Stale Post-EOF Pagecache\n+---------------------------------\n+\n+When a file is extended, data left in the pagecache past the old EOF by a write\n+through an mmap must not be exposed as file content. Netfslib clears this on\n+its own write paths, and exports a helper so a filesystem can do the same from,\n+for instance, its truncate or fallocate paths::\n+\n+\tint netfs_clear_stale_post_eof(struct inode *inode, unsigned long long from,\n+\t\t\t\t unsigned long long to, bool nowait);\n+\n+This zeroes any such data within the ``[from, to)`` hole to be made, where @from\n+is the current EOF. Only the folio straddling @from can hold data written past\n+the EOF through an mmap, as pages wholly beyond the EOF can't be faulted in, so\n+the zeroing is limited to that folio and clamped to the top of the hole. The\n+folio is zeroed rather than dropped so that a concurrent extending write can't\n+lose data. If @nowait is set, it returns ``-EAGAIN`` rather than blocking.\n+\n High-Level VM API\n ==================\n \ndiff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c\nindex 2cdb68e6b16ff..cc0561f77bd08 100644\n--- a/fs/netfs/buffered_write.c\n+++ b/fs/netfs/buffered_write.c\n@@ -469,6 +469,7 @@ ssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *fr\n \t\t\t\t\t struct netfs_group *netfs_group)\n {\n \tstruct file *file = iocb-\u003eki_filp;\n+\tstruct inode *inode = file_inode(file);\n \tssize_t ret;\n \n \ttrace_netfs_write_iter(iocb, from);\n@@ -481,6 +482,14 @@ ssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *fr\n \tif (ret)\n \t\treturn ret;\n \n+\tif (iocb-\u003eki_pos \u003e i_size_read(inode)) {\n+\t\tret = netfs_clear_stale_post_eof(inode, i_size_read(inode),\n+\t\t\t\t\t\t iocb-\u003eki_pos,\n+\t\t\t\t\t\t iocb-\u003eki_flags \u0026 IOCB_NOWAIT);\n+\t\tif (ret)\n+\t\t\treturn ret;\n+\t}\n+\n \treturn netfs_perform_write(iocb, from, netfs_group);\n }\n EXPORT_SYMBOL(netfs_buffered_write_iter_locked);\ndiff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c\nindex 2361277416c73..36c36bc6c9d26 100644\n--- a/fs/netfs/direct_write.c\n+++ b/fs/netfs/direct_write.c\n@@ -359,6 +359,15 @@ ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from)\n \tret = file_update_time(file);\n \tif (ret \u003c 0)\n \t\tgoto out;\n+\n+\tif (iocb-\u003eki_pos \u003e i_size_read(inode)) {\n+\t\tret = netfs_clear_stale_post_eof(inode, i_size_read(inode),\n+\t\t\t\t\t\t iocb-\u003eki_pos,\n+\t\t\t\t\t\t iocb-\u003eki_flags \u0026 IOCB_NOWAIT);\n+\t\tif (ret \u003c 0)\n+\t\t\tgoto out;\n+\t}\n+\n \tif (iocb-\u003eki_flags \u0026 IOCB_NOWAIT) {\n \t\t/* We could block if there are any pages in the range. */\n \t\tret = -EAGAIN;\ndiff --git a/fs/netfs/misc.c b/fs/netfs/misc.c\nindex f5c1c463f4ff7..b9ca24b3dfdae 100644\n--- a/fs/netfs/misc.c\n+++ b/fs/netfs/misc.c\n@@ -6,6 +6,7 @@\n */\n \n #include \u003clinux/swap.h\u003e\n+#include \u003clinux/rmap.h\u003e\n #include \"internal.h\"\n \n /**\n@@ -582,3 +583,53 @@ void netfs_wait_for_put_ra_refs(struct netfs_io_request *rreq)\n \ttrace_netfs_rreq(rreq, netfs_rreq_trace_waited_put_ra_refs);\n \tfinish_wait(\u0026rreq-\u003ewaitq, \u0026myself);\n }\n+\n+/**\n+ * netfs_clear_stale_post_eof - Clear stale pagecache in a to-be-created hole\n+ * @inode: The inode to act upon.\n+ * @from: The base of the hole to be made (the current EOF).\n+ * @to: The top of the hole to be made.\n+ * @nowait: True to return -EAGAIN rather than block.\n+ *\n+ * Before extending a file, zero any data left in the pagecache within the\n+ * [@from, @to) hole by a write through an mmap so that it isn't exposed as file\n+ * content once the file is extended. Only the uptodate folio straddling @from\n+ * can hold such data as pages wholly beyond the EOF can't be faulted in, so the\n+ * zeroing is limited to that folio. The folio is zeroed rather than dropped so\n+ * that a concurrent extending write can't lose data.\n+ *\n+ * Return: 0 on success, or -EAGAIN if @nowait is set and the folio would need\n+ * to be waited on.\n+ */\n+int netfs_clear_stale_post_eof(struct inode *inode, unsigned long long from,\n+\t\t\t unsigned long long to, bool nowait)\n+{\n+\tstruct address_space *mapping = inode-\u003ei_mapping;\n+\tfgf_t fgp = FGP_LOCK;\n+\tstruct folio *folio;\n+\n+\tif (from \u003e= to)\n+\t\treturn 0;\n+\n+\tif (nowait)\n+\t\tfgp |= FGP_NOWAIT;\n+\n+\tfolio = __filemap_get_folio(mapping, from \u003e\u003e PAGE_SHIFT, fgp, 0);\n+\tif (IS_ERR(folio))\n+\t\treturn PTR_ERR(folio) == -EAGAIN ? -EAGAIN : 0;\n+\n+\tif (folio_mkclean(folio))\n+\t\tfolio_mark_dirty(folio);\n+\n+\tif (folio_test_uptodate(folio)) {\n+\t\tsize_t end = umin(to - folio_pos(folio), folio_size(folio));\n+\t\tsize_t offset = offset_in_folio(folio, from);\n+\n+\t\tfolio_zero_segment(folio, offset, end);\n+\t}\n+\n+\tfolio_unlock(folio);\n+\tfolio_put(folio);\n+\treturn 0;\n+}\n+EXPORT_SYMBOL(netfs_clear_stale_post_eof);\ndiff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c\nindex 7ecd70efdfea8..6410249f529a2 100644\n--- a/fs/smb/client/cifsfs.c\n+++ b/fs/smb/client/cifsfs.c\n@@ -1467,9 +1467,14 @@ static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,\n \ti_size = target_inode-\u003ei_size;\n \tspin_unlock(\u0026target_inode-\u003ei_lock);\n \n-\t/* Discard all the folios that overlap the destination region. */\n+\t/*\n+\t * Discard all the folios that overlap the destination region. Start at\n+\t * the old EOF when extending so the folio straddling it, which may hold\n+\t * data written past EOF through an mmap, is dropped too.\n+\t */\n \tcifs_dbg(FYI, \"about to discard pages %llx-%llx\\n\", fstart, fend);\n-\ttruncate_inode_pages_range(\u0026target_inode-\u003ei_data, fstart, fend);\n+\ttruncate_inode_pages_range(\u0026target_inode-\u003ei_data,\n+\t\t\t\t min(fstart, i_size), fend);\n \n \tfscache_invalidate(cifs_inode_cookie(target_inode), NULL, i_size, 0);\n \n@@ -1581,8 +1586,13 @@ ssize_t cifs_file_copychunk_range(unsigned int xid,\n \t/* Flush and invalidate all the folios in the destination region. If\n \t * the copy was successful, then some of the flush is extra overhead,\n \t * but we need to allow for the copy failing in some way (eg. ENOSPC).\n+\t *\n+\t * Start at the old EOF when extending so the folio straddling it, which\n+\t * may hold data written past EOF through an mmap, is dropped too.\n \t */\n-\trc = filemap_invalidate_inode(target_inode, true, destoff, destoff + len - 1);\n+\trc = filemap_invalidate_inode(target_inode, true,\n+\t\t\t\t min(destoff, i_size_read(target_inode)),\n+\t\t\t\t destoff + len - 1);\n \tif (rc)\n \t\tgoto unlock;\n \ndiff --git a/fs/smb/client/inode.c b/fs/smb/client/inode.c\nindex 1fe0ef0a95dbd..9abb40f871c66 100644\n--- a/fs/smb/client/inode.c\n+++ b/fs/smb/client/inode.c\n@@ -3071,8 +3071,16 @@ void cifs_setsize(struct inode *inode, loff_t offset)\n \t\tinode-\u003ei_blocks = blocks;\n \tspin_unlock(\u0026inode-\u003ei_lock);\n \tinode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));\n+\t/*\n+\t * When extending, zero the tail of the folio straddling the old EOF\n+\t * so that data dirtied past EOF through an mmap isn't exposed once the\n+\t * file is extended. This mirrors pagecache_isize_extended(), which\n+\t * can't be used here as it is a no-op when the block size is \u003e=\n+\t * PAGE_SIZE, as on CIFS. truncate_pagecache() then drops the\n+\t * pagecache beyond the new EOF, as in truncate_setsize().\n+\t */\n \tif (offset \u003e old_size)\n-\t\tpagecache_isize_extended(inode, old_size, offset);\n+\t\tnetfs_clear_stale_post_eof(inode, old_size, offset, false);\n \ttruncate_pagecache(inode, offset);\n \tnetfs_wait_for_outstanding_io(inode);\n }\ndiff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c\nindex 3464470d32977..7282ed9164705 100644\n--- a/fs/smb/client/smb2ops.c\n+++ b/fs/smb/client/smb2ops.c\n@@ -3558,8 +3558,11 @@ static long smb3_zero_range(struct file *file, struct cifs_tcon *tcon,\n \t/*\n \t * We zero the range through ioctl, so we need remove the page caches\n \t * first, otherwise the data may be inconsistent with the server.\n+\t *\n+\t * Start at the old EOF when extending so the folio straddling it, which\n+\t * may hold data written past EOF through an mmap, is dropped too.\n \t */\n-\ttruncate_pagecache_range(inode, offset, offset + len - 1);\n+\ttruncate_pagecache_range(inode, min(offset, i_size), offset + len - 1);\n \tnetfs_wait_for_outstanding_io(inode);\n \n \t/* if file not oplocked can't be sure whether asking to extend size */\ndiff --git a/include/linux/netfs.h b/include/linux/netfs.h\nindex b4dd32863dd45..2981290b9a77a 100644\n--- a/include/linux/netfs.h\n+++ b/include/linux/netfs.h\n@@ -397,6 +397,8 @@ ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from);\n ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *iter,\n \t\t\t\t\t struct netfs_group *netfs_group);\n ssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from);\n+int netfs_clear_stale_post_eof(struct inode *inode, unsigned long long from,\n+\t\t\t unsigned long long to, bool nowait);\n \n /* Single, monolithic object read/write API. */\n void netfs_single_mark_inode_dirty(struct inode *inode);\n"
} |
| 2/1 | 2026/09/24 01:07 | agent | patch-evaluator |
1mModel:core Args: null Results: {
"EnableConfigs": [
"NETFS_SUPPORT",
"CIFS",
"9P_FS",
"NET_9P"
],
"FocusSymbols": [
"netfs_clear_stale_post_eof",
"netfs_buffered_write_iter_locked",
"netfs_unbuffered_write_iter",
"cifs_setsize",
"cifs_remap_file_range",
"cifs_file_copychunk_range",
"smb3_zero_range"
],
"Reasoning": "The patch series modifies core netfs and CIFS pagecache handling when extending files or operating on file ranges. It introduces `netfs_clear_stale_post_eof()` to clear and clean stale post-EOF pagecache folios dirtied via mmap before extending a file, and integrates it into netfs buffered/unbuffered write paths and CIFS setsize/range operations. These are reachable file operations in virtualized environments (e.g. via 9p or CIFS/SMB loopback) involving folio locking, clean/dirty state transitions, and pagecache truncation, warranting fuzzing.",
"WorthFuzzing": true
}Instruction: You are an expert Linux kernel maintainer and security engineer.
Your job is to review a provided patch series and evaluate whether it warrants fuzzing with syzkaller.
IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on internal assumptions. You must actively use your code access
tools to inspect the actual source code, callers, and surrounding context.
================================================================================
1. CORE TRIAGE PHILOSOPHY
================================================================================
The goal of patch fuzzing is to discover crashes, regressions, exposed latent bugs,
and newly triggered assertions introduced by the patch series.
- REACHABILITY IS THE PRIMARY GATE:
Fuzzing can only discover bugs in code that can actually execute in standard virtualized
environments (GCE or QEMU, utilizing software-emulated devices like USB gadgets, netdev, tun/tap).
If the modified code is structurally unreachable (see Section 2), it MUST NOT be fuzzed,
regardless of whether it adds assertions or complex logic.
- DO NOT BLINDLY TRUST "NO FUNCTIONAL CHANGE" (NFCI) OR "REFACTORING" CLAIMS:
Patch authors routinely label changes as "cleanups", "refactorings", or state
"No functional change intended". Do NOT take these claims at face value.
Code refactorings that rearrange logic, introduce helper functions, or alter state management
in core subsystems frequently introduce subtle semantic shifts or uncover latent kernel bugs.
If reachable executable code is modified or refactored, it MUST be fuzzed.
- NEW OR MODIFIED ASSERTIONS IN REACHABLE CODE MUST BE FUZZED:
When a patch introduces or modifies runtime checks or assertions (e.g., WARN_ON*, VM_WARN_ON*,
BUG_ON*, lockdep_assert*) in reachable code paths, it enforces new or stricter invariants.
Even if the author believes the invariant always holds, fuzzing is essential to verify whether
an unusual sequence of operations can violate it.
================================================================================
2. WHEN TO RETURN WorthFuzzing=false (NEGATIVE CRITERIA)
================================================================================
Return WorthFuzzing=false ONLY IF all modified code falls strictly into one or more of these categories:
- Non-kernel and non-executable changes:
* Modifications to Documentation/, comments, or spelling fixes.
* User-space directories, self-tests, samples, or scripts (e.g., tools/, samples/, scripts/, usr/)
that do not affect the compiled kernel image (vmlinux) or kernel modules.
* Purely decorative logging (e.g., message strings in pr_err, printk, dev_info) or tracepoints
that do not alter control flow or data structures.
* Build system or Kconfig changes that do not alter compiled C logic.
- Structurally unreachable hardware:
* Vendor-specific PCIe switches, SmartNICs, or GPU drivers (e.g., mlxsw, pds_core, qed,
ionic, amdgpu) requiring physical ASIC/PCIe cards not emulated in standard QEMU.
- Unreachable execution paths:
* Driver teardown callbacks (.remove, .shutdown, pci_unregister_driver) executed only during
physical PCI hot-unplug or manual sysfs driver unbinding.
* Code paths exclusive to architectures other than the target architecture.
================================================================================
3. WHEN TO RETURN WorthFuzzing=true (POSITIVE CRITERIA)
================================================================================
Return WorthFuzzing=true whenever the patch touches reachable executable code, including:
- Core Subsystems:
* Any logic modifications in memory management (mm/), synchronization/locking (kernel/locking/),
BPF, scheduler, core networking, VFS, or syscall handling.
- Refactorings and Code Cleanups:
* Any restructuring of reachable data structures, helper abstractions, or algorithm flows.
- Runtime Assertions and Defensive Checks:
* Any introduction or alteration of assertions (WARN_ON*, VM_WARN_ON*, BUG_ON*, etc.) in reachable paths.
- Reachable Drivers and Protocols:
* Drivers accessible via virtual buses (virtio, USB gadget, loopback, netlink, binder, sockets, etc.).
================================================================================
4. EXTRACTING FocusSymbols (PREVENTING DILUTION)
================================================================================
When WorthFuzzing=true, you must extract specific kernel functions into FocusSymbols to guide the fuzzer:
- AVOID UBIQUITOUS LIFECYCLE HOT-PATHS:
Do NOT list generic, ubiquitous functions called by almost every program in the corpus
(including, but not limited to: general memory allocators and deallocators, page fault
and trap handlers, or core synchronization primitives; this is not an exhaustive list).
Listing ubiquitous functions causes the fuzzer to classify thousands of unrelated tests as "focused",
which severely dilutes fuzzing effort away from the actual changes.
- TARGET SPECIFIC FEATURE LOGIC AND ENTRYPOINTS:
List functions that specifically implement the logic being added or altered, or direct API entrypoints
for the subsystem feature under review.
- HANDLING STATIC INLINE FUNCTIONS IN HEADERS (.h):
Compiler-inlined static functions (such as static inlines in mm/*.h or include/linux/*.h) lack
distinct symbol addresses in vmlinux and cannot be targeted directly by symbol coverage filters.
If the changes are primarily in static inline helpers, identify non-static, feature-specific caller
functions in .c files that exercise them (avoiding ubiquitous lifecycle wrappers).
================================================================================
5. IDENTIFYING EnableConfigs
================================================================================
Identify any specific CONFIG_ options required to properly compile and reach the modified code:
- Inspect Kconfig files and #ifdef guards; do not make assumptions.
- Check "depends on" lines in Kconfig to include any non-standard parent subsystem configs needed.
- Strip any 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt: Target architecture: amd64
For your convenience, here is the diff of the changes:
commit ffe5c0db81fb5e586f5ad7fe7cabab11275ed0d4
Author: syz-cluster <triage@syzkaller.com>
Date: Thu Sep 24 01:07:46 2026 +0000
syz-cluster: applied patch under review
diff --git a/Documentation/filesystems/netfs_library.rst b/Documentation/filesystems/netfs_library.rst
index ddd799df6ce36..58b0adacc2f3e 100644
--- a/Documentation/filesystems/netfs_library.rst
+++ b/Documentation/filesystems/netfs_library.rst
@@ -451,6 +451,24 @@ one.
The inode should be marked ``NETFS_ICTX_SINGLE_NO_UPLOAD`` if this API is to be
used. The writeback function requires the buffer to be of ITER_FOLIOQ type.
+Clearing Stale Post-EOF Pagecache
+---------------------------------
+
+When a file is extended, data left in the pagecache past the old EOF by a write
+through an mmap must not be exposed as file content. Netfslib clears this on
+its own write paths, and exports a helper so a filesystem can do the same from,
+for instance, its truncate or fallocate paths::
+
+ int netfs_clear_stale_post_eof(struct inode *inode, unsigned long long from,
+ unsigned long long to, bool nowait);
+
+This zeroes any such data within the ``[from, to)`` hole to be made, where @from
+is the current EOF. Only the folio straddling @from can hold data written past
+the EOF through an mmap, as pages wholly beyond the EOF can't be faulted in, so
+the zeroing is limited to that folio and clamped to the top of the hole. The
+folio is zeroed rather than dropped so that a concurrent extending write can't
+lose data. If @nowait is set, it returns ``-EAGAIN`` rather than blocking.
+
High-Level VM API
==================
diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
index 2cdb68e6b16ff..cc0561f77bd08 100644
--- a/fs/netfs/buffered_write.c
+++ b/fs/netfs/buffered_write.c
@@ -469,6 +469,7 @@ ssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *fr
struct netfs_group *netfs_group)
{
struct file *file = iocb->ki_filp;
+ struct inode *inode = file_inode(file);
ssize_t ret;
trace_netfs_write_iter(iocb, from);
@@ -481,6 +482,14 @@ ssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *fr
if (ret)
return ret;
+ if (iocb->ki_pos > i_size_read(inode)) {
+ ret = netfs_clear_stale_post_eof(inode, i_size_read(inode),
+ iocb->ki_pos,
+ iocb->ki_flags & IOCB_NOWAIT);
+ if (ret)
+ return ret;
+ }
+
return netfs_perform_write(iocb, from, netfs_group);
}
EXPORT_SYMBOL(netfs_buffered_write_iter_locked);
diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c
index 2361277416c73..36c36bc6c9d26 100644
--- a/fs/netfs/direct_write.c
+++ b/fs/netfs/direct_write.c
@@ -359,6 +359,15 @@ ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from)
ret = file_update_time(file);
if (ret < 0)
goto out;
+
+ if (iocb->ki_pos > i_size_read(inode)) {
+ ret = netfs_clear_stale_post_eof(inode, i_size_read(inode),
+ iocb->ki_pos,
+ iocb->ki_flags & IOCB_NOWAIT);
+ if (ret < 0)
+ goto out;
+ }
+
if (iocb->ki_flags & IOCB_NOWAIT) {
/* We could block if there are any pages in the range. */
ret = -EAGAIN;
diff --git a/fs/netfs/misc.c b/fs/netfs/misc.c
index f5c1c463f4ff7..b9ca24b3dfdae 100644
--- a/fs/netfs/misc.c
+++ b/fs/netfs/misc.c
@@ -6,6 +6,7 @@
*/
#include <linux/swap.h>
+#include <linux/rmap.h>
#include "internal.h"
/**
@@ -582,3 +583,53 @@ void netfs_wait_for_put_ra_refs(struct netfs_io_request *rreq)
trace_netfs_rreq(rreq, netfs_rreq_trace_waited_put_ra_refs);
finish_wait(&rreq->waitq, &myself);
}
+
+/**
+ * netfs_clear_stale_post_eof - Clear stale pagecache in a to-be-created hole
+ * @inode: The inode to act upon.
+ * @from: The base of the hole to be made (the current EOF).
+ * @to: The top of the hole to be made.
+ * @nowait: True to return -EAGAIN rather than block.
+ *
+ * Before extending a file, zero any data left in the pagecache within the
+ * [@from, @to) hole by a write through an mmap so that it isn't exposed as file
+ * content once the file is extended. Only the uptodate folio straddling @from
+ * can hold such data as pages wholly beyond the EOF can't be faulted in, so the
+ * zeroing is limited to that folio. The folio is zeroed rather than dropped so
+ * that a concurrent extending write can't lose data.
+ *
+ * Return: 0 on success, or -EAGAIN if @nowait is set and the folio would need
+ * to be waited on.
+ */
+int netfs_clear_stale_post_eof(struct inode *inode, unsigned long long from,
+ unsigned long long to, bool nowait)
+{
+ struct address_space *mapping = inode->i_mapping;
+ fgf_t fgp = FGP_LOCK;
+ struct folio *folio;
+
+ if (from >= to)
+ return 0;
+
+ if (nowait)
+ fgp |= FGP_NOWAIT;
+
+ folio = __filemap_get_folio(mapping, from >> PAGE_SHIFT, fgp, 0);
+ if (IS_ERR(folio))
+ return PTR_ERR(folio) == -EAGAIN ? -EAGAIN : 0;
+
+ if (folio_mkclean(folio))
+ folio_mark_dirty(folio);
+
+ if (folio_test_uptodate(folio)) {
+ size_t end = umin(to - folio_pos(folio), folio_size(folio));
+ size_t offset = offset_in_folio(folio, from);
+
+ folio_zero_segment(folio, offset, end);
+ }
+
+ folio_unlock(folio);
+ folio_put(folio);
+ return 0;
+}
+EXPORT_SYMBOL(netfs_clear_stale_post_eof);
diff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c
index 7ecd70efdfea8..6410249f529a2 100644
--- a/fs/smb/client/cifsfs.c
+++ b/fs/smb/client/cifsfs.c
@@ -1467,9 +1467,14 @@ static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,
i_size = target_inode->i_size;
spin_unlock(&target_inode->i_lock);
- /* Discard all the folios that overlap the destination region. */
+ /*
+ * Discard all the folios that overlap the destination region. Start at
+ * the old EOF when extending so the folio straddling it, which may hold
+ * data written past EOF through an mmap, is dropped too.
+ */
cifs_dbg(FYI, "about to discard pages %llx-%llx\n", fstart, fend);
- truncate_inode_pages_range(&target_inode->i_data, fstart, fend);
+ truncate_inode_pages_range(&target_inode->i_data,
+ min(fstart, i_size), fend);
fscache_invalidate(cifs_inode_cookie(target_inode), NULL, i_size, 0);
@@ -1581,8 +1586,13 @@ ssize_t cifs_file_copychunk_range(unsigned int xid,
/* Flush and invalidate all the folios in the destination region. If
* the copy was successful, then some of the flush is extra overhead,
* but we need to allow for the copy failing in some way (eg. ENOSPC).
+ *
+ * Start at the old EOF when extending so the folio straddling it, which
+ * may hold data written past EOF through an mmap, is dropped too.
*/
- rc = filemap_invalidate_inode(target_inode, true, destoff, destoff + len - 1);
+ rc = filemap_invalidate_inode(target_inode, true,
+ min(destoff, i_size_read(target_inode)),
+ destoff + len - 1);
if (rc)
goto unlock;
diff --git a/fs/smb/client/inode.c b/fs/smb/client/inode.c
index 1fe0ef0a95dbd..9abb40f871c66 100644
--- a/fs/smb/client/inode.c
+++ b/fs/smb/client/inode.c
@@ -3071,8 +3071,16 @@ void cifs_setsize(struct inode *inode, loff_t offset)
inode->i_blocks = blocks;
spin_unlock(&inode->i_lock);
inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
+ /*
+ * When extending, zero the tail of the folio straddling the old EOF
+ * so that data dirtied past EOF through an mmap isn't exposed once the
+ * file is extended. This mirrors pagecache_isize_extended(), which
+ * can't be used here as it is a no-op when the block size is >=
+ * PAGE_SIZE, as on CIFS. truncate_pagecache() then drops the
+ * pagecache beyond the new EOF, as in truncate_setsize().
+ */
if (offset > old_size)
- pagecache_isize_extended(inode, old_size, offset);
+ netfs_clear_stale_post_eof(inode, old_size, offset, false);
truncate_pagecache(inode, offset);
netfs_wait_for_outstanding_io(inode);
}
diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index 3464470d32977..7282ed9164705 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -3558,8 +3558,11 @@ static long smb3_zero_range(struct file *file, struct cifs_tcon *tcon,
/*
* We zero the range through ioctl, so we need remove the page caches
* first, otherwise the data may be inconsistent with the server.
+ *
+ * Start at the old EOF when extending so the folio straddling it, which
+ * may hold data written past EOF through an mmap, is dropped too.
*/
- truncate_pagecache_range(inode, offset, offset + len - 1);
+ truncate_pagecache_range(inode, min(offset, i_size), offset + len - 1);
netfs_wait_for_outstanding_io(inode);
/* if file not oplocked can't be sure whether asking to extend size */
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index b4dd32863dd45..2981290b9a77a 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -397,6 +397,8 @@ ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from);
ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *iter,
struct netfs_group *netfs_group);
ssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from);
+int netfs_clear_stale_post_eof(struct inode *inode, unsigned long long from,
+ unsigned long long to, bool nowait);
/* Single, monolithic object read/write API. */
void netfs_single_mark_inode_dirty(struct inode *inode);
|
| 3/2 | 2026/09/24 01:07 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 6217 output: 22 thoughts: 935 Thoughts: **Analyzing the Patch for Fuzzing Potential** Okay, let's break this patch down and figure out if it's worth a fuzzing campaign with syzkaller. First, the diff overview shows changes across `Documentation/filesystems/netfs_library.rst`, and then within several files under `fs/netfs/` and `fs/smb/client/`. This suggests either a core netfs functionality alteration or integration into the SMB client. Looking at the code changes, a key function, `netfs_clear_stale_post_eof`, stands out in `fs/netfs/misc.c`. It seems to be responsible for clearing stale data beyond the current file size (i_size) after an operation. It uses `__filemap_get_folio`, potentially working with folios to zero out segments using folio APIs. I see calls to this from `netfs_buffered_write_iter_locked` and `netfs_unbuffered_write_iter` in buffered and direct write code paths, as well as `cifs_setsize`. There's also `truncate_inode_pages_range`, `filemap_invalidate_inode`, and `truncate_pagecache_range` being used, often with the `min(offset, i_size)` construct. This truncation logic, along with `netfs_clear_stale_post_eof`, is probably related to handling file size changes and preventing data leaks/corruption in various write scenarios (specifically writing beyond the current file size), or truncation logic to ensure the correct contents are visible post-write. Since `netfs_clear_stale_post_eof` seems to be called from write operations, and potentially from the SMB client, this could introduce interesting fuzzing targets. Now I'll use `grepper` to determine which filesystems actually make use of these netfs write paths. If the SMB client relies heavily on netfs, we could have a potentially higher-value fuzzing target, as file sharing systems have historically been a source of many vulnerabilities. I'll focus on the interaction between write operations and this `netfs_clear_stale_post_eof` function. I will determine if the filesystem relies on it, and what happens if the data is stale. Then, I will evaluate the potential for race conditions or incorrect calculations of file size/offset, particularly if we can control `ki_pos`, `i_size`, and the offset in the folio. |
| 4/2 | 2026/09/24 01:08 | tool | grepper |
0mArgs:{
"Expression": "netfs_buffered_write_iter"
}Results: {
"Output": "Documentation/filesystems/netfs_library.rst=397=There are three functions for writes::\nDocumentation/filesystems/netfs_library.rst-398-\nDocumentation/filesystems/netfs_library.rst:399:\tssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *from,\nDocumentation/filesystems/netfs_library.rst-400-\t\t\t\t\t\t struct netfs_group *netfs_group);\n--\nfs/netfs/buffered_write.c=443=EXPORT_SYMBOL(netfs_perform_write);\n--\nfs/netfs/buffered_write.c-445-/**\nfs/netfs/buffered_write.c:446: * netfs_buffered_write_iter_locked - write data to a file\nfs/netfs/buffered_write.c-447- * @iocb:\tIO state structure (file, offset, etc.)\n--\nfs/netfs/buffered_write.c-467- */\nfs/netfs/buffered_write.c:468:ssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *from,\nfs/netfs/buffered_write.c-469-\t\t\t\t\t struct netfs_group *netfs_group)\n--\nfs/netfs/buffered_write.c-494-}\nfs/netfs/buffered_write.c:495:EXPORT_SYMBOL(netfs_buffered_write_iter_locked);\nfs/netfs/buffered_write.c-496-\n--\nfs/netfs/buffered_write.c=510=ssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)\n--\nfs/netfs/buffered_write.c-531-\tif (ret \u003e 0)\nfs/netfs/buffered_write.c:532:\t\tret = netfs_buffered_write_iter_locked(iocb, from, NULL);\nfs/netfs/buffered_write.c-533-\tnetfs_end_io_write(inode);\n--\nfs/smb/client/file.c=2977=cifs_writev(struct kiocb *iocb, struct iov_iter *from)\n--\nfs/smb/client/file.c-3008-\nfs/smb/client/file.c:3009:\trc = netfs_buffered_write_iter_locked(iocb, from, NULL);\nfs/smb/client/file.c-3010-\tcifs_update_i_blocks_after_write(iocb, rc);\n--\ninclude/linux/netfs.h=392=ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,\ninclude/linux/netfs.h-393-\t\t\t struct netfs_group *netfs_group);\ninclude/linux/netfs.h:394:ssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *from,\ninclude/linux/netfs.h-395-\t\t\t\t\t struct netfs_group *netfs_group);\n"
} |
| 5/2 | 2026/09/24 01:08 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 8511 output: 22 thoughts: 28 Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience: **Analyzing `netfs_file_write_iter` and `netfs_unbuffered_write_iter` Usage** Alright, let's get down to brass tacks. I need to understand the current landscape of `netfs_file_write_iter` and `netfs_unbuffered_write_iter` within the system. My initial thought process is geared towards understanding where these functions are *actually* being employed. I want to identify the call sites; what higher-level components or subsystems are leveraging these iterators for writing to netfs? Are we talking primarily about specific network file systems like NFS or SMB? Or is the use more widespread than that, encompassing more generalized data streaming or caching operations? The distinction between these two functions immediately sparks some deeper questions. Is one preferred over the other? If so, why? I'll need to dig into the rationale behind their distinct implementations. Is `netfs_unbuffered_write_iter` specifically aimed at scenarios where buffering is undesirable (for example, latency-sensitive applications) or perhaps when managing limited memory or direct hardware access? Conversely, does the presence of `netfs_file_write_iter` suggest a design decision to allow for buffering in order to optimize I/O throughput? Essentially, my goal isn't just to see *if* they're used, but *how* they're used. I'm looking for the context. I'll need to determine the common patterns and any potential areas of concern, optimization opportunities, or latent performance bottlenecks that may have been overlooked or misidentified. This analysis is going to be pivotal in either verifying or improving the overall architecture of netfs. |
| 6/2 | 2026/09/24 01:08 | tool | grepper |
0mArgs:{
"Expression": "netfs_file_write_iter"
}Results: {
"Output": "Documentation/filesystems/netfs_library.rst=371=filesystem is called through the standard VFS read/write_iter methods::\n--\nDocumentation/filesystems/netfs_library.rst-373-\tssize_t netfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter);\nDocumentation/filesystems/netfs_library.rst:374:\tssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from);\nDocumentation/filesystems/netfs_library.rst-375-\tssize_t netfs_buffered_read_iter(struct kiocb *iocb, struct iov_iter *iter);\n--\nfs/9p/vfs_file.c=401=v9fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)\n--\nfs/9p/vfs_file.c-411-\tp9_debug(P9_DEBUG_CACHE, \"(cached)\\n\");\nfs/9p/vfs_file.c:412:\treturn netfs_file_write_iter(iocb, from);\nfs/9p/vfs_file.c-413-}\n--\nfs/afs/file.c=34=const struct file_operations afs_file_operations = {\n--\nfs/afs/file.c-38-\t.read_iter\t= afs_file_read_iter,\nfs/afs/file.c:39:\t.write_iter\t= netfs_file_write_iter,\nfs/afs/file.c-40-\t.mmap_prepare\t= afs_file_mmap_prepare,\n--\nfs/netfs/buffered_write.c=495=EXPORT_SYMBOL(netfs_buffered_write_iter_locked);\n--\nfs/netfs/buffered_write.c-497-/**\nfs/netfs/buffered_write.c:498: * netfs_file_write_iter - write data to a file\nfs/netfs/buffered_write.c-499- * @iocb: IO state structure\n--\nfs/netfs/buffered_write.c-509- */\nfs/netfs/buffered_write.c:510:ssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)\nfs/netfs/buffered_write.c-511-{\n--\nfs/netfs/buffered_write.c-537-}\nfs/netfs/buffered_write.c:538:EXPORT_SYMBOL(netfs_file_write_iter);\nfs/netfs/buffered_write.c-539-\n--\nfs/smb/client/file.c=3021=cifs_strict_writev(struct kiocb *iocb, struct iov_iter *from)\n--\nfs/smb/client/file.c-3038-\t\t ((cifs_sb_flags(cifs_sb) \u0026 CIFS_MOUNT_NOPOSIXBRL) == 0)) {\nfs/smb/client/file.c:3039:\t\t\twritten = netfs_file_write_iter(iocb, from);\nfs/smb/client/file.c-3040-\t\t\tcifs_update_i_blocks_after_write(iocb, written);\n--\nfs/smb/client/file.c-3051-\t */\nfs/smb/client/file.c:3052:\twritten = netfs_file_write_iter(iocb, from);\nfs/smb/client/file.c-3053-\tcifs_update_i_blocks_after_write(iocb, written);\n--\nfs/smb/client/file.c=3072=ssize_t cifs_direct_write_iter(struct kiocb *iocb, struct iov_iter *from)\n--\nfs/smb/client/file.c-3075-\nfs/smb/client/file.c:3076:\twritten = netfs_file_write_iter(iocb, from);\nfs/smb/client/file.c-3077-\tcifs_update_i_blocks_after_write(iocb, written);\n--\nfs/smb/client/file.c=3096=ssize_t cifs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)\n--\nfs/smb/client/file.c-3119-\nfs/smb/client/file.c:3120:\twritten = netfs_file_write_iter(iocb, from);\nfs/smb/client/file.c-3121-\tcifs_update_i_blocks_after_write(iocb, written);\n--\ninclude/linux/netfs.h=397=ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *iter,\ninclude/linux/netfs.h-398-\t\t\t\t\t struct netfs_group *netfs_group);\ninclude/linux/netfs.h:399:ssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from);\ninclude/linux/netfs.h-400-int netfs_clear_stale_post_eof(struct inode *inode, unsigned long long from,\n"
} |
| 7/2 | 2026/09/24 01:08 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 10297 output: 23 thoughts: 216 Thoughts: **Filesystem Protocol Exploration** Okay, so I'm looking at this and my mind immediately jumps to the interesting filesystem clients we have, specifically `9p`, `afs`, and `cifs`, or more commonly known as SMB client. Interesting, `9p` in particular is extensively tested by syzkaller, which is great. It's using either virtio-9p or loopback/socket, but the real takeaway is that you can mount 9p over virtio or TCP directly within syzkaller. Now, a critical thought: can 9p function in QEMU without direct hardware involvement? Yes! Virtio-9p is pretty standard in syzkaller's QEMU environment, or even using trans=fd. That's a powerful setup for testing. The next question: can we achieve something similar with `cifs` using loopback? I need to look into whether the CIFS/SMB client can be mounted locally if there's an SMB server running. Thinking in terms of `trans=fd` or some sort of network loopback, I'm thinking of interesting local testing capabilities. And now, for deeper analysis: I need to examine the 9p file system's `v9fs_file_write_iter` path. This leads to `netfs_file_write_iter`, which then goes to `netfs_buffered_write_iter_locked` and finally to `netfs_clear_stale_post_eof`. I have to dig into these functions. One more thing to consider: I should also check Ceph and other filesystems that utilize netfs. There are likely other interesting things to investigate in that context. |
| 8/2 | 2026/09/24 01:08 | tool | grepper |
0mArgs:{
"Expression": "netfs_unbuffered_write_iter"
}Results: {
"Output": "Documentation/filesystems/netfs_library.rst=371=filesystem is called through the standard VFS read/write_iter methods::\n--\nDocumentation/filesystems/netfs_library.rst-376-\tssize_t netfs_unbuffered_read_iter(struct kiocb *iocb, struct iov_iter *iter);\nDocumentation/filesystems/netfs_library.rst:377:\tssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from);\nDocumentation/filesystems/netfs_library.rst-378-\n--\nDocumentation/filesystems/netfs_library.rst=397=There are three functions for writes::\n--\nDocumentation/filesystems/netfs_library.rst-402-\t\t\t\t struct netfs_group *netfs_group);\nDocumentation/filesystems/netfs_library.rst:403:\tssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *iter,\nDocumentation/filesystems/netfs_library.rst-404-\t\t\t\t\t\t struct netfs_group *netfs_group);\n--\nfs/9p/vfs_file.c=401=v9fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)\n--\nfs/9p/vfs_file.c-408-\tif (fid-\u003emode \u0026 (P9L_DIRECT | P9L_NOWRITECACHE))\nfs/9p/vfs_file.c:409:\t\treturn netfs_unbuffered_write_iter(iocb, from);\nfs/9p/vfs_file.c-410-\n--\nfs/netfs/buffered_write.c=510=ssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)\n--\nfs/netfs/buffered_write.c-523-\t test_bit(NETFS_ICTX_UNBUFFERED, \u0026ictx-\u003eflags))\nfs/netfs/buffered_write.c:524:\t\treturn netfs_unbuffered_write_iter(iocb, from);\nfs/netfs/buffered_write.c-525-\n--\nfs/netfs/direct_write.c=212=static void netfs_unbuffered_write_async(struct work_struct *work)\n--\nfs/netfs/direct_write.c-223- */\nfs/netfs/direct_write.c:224:ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *iter,\nfs/netfs/direct_write.c-225-\t\t\t\t\t\t struct netfs_group *netfs_group)\n--\nfs/netfs/direct_write.c-316-}\nfs/netfs/direct_write.c:317:EXPORT_SYMBOL(netfs_unbuffered_write_iter_locked);\nfs/netfs/direct_write.c-318-\nfs/netfs/direct_write.c-319-/**\nfs/netfs/direct_write.c:320: * netfs_unbuffered_write_iter - Unbuffered write to a file\nfs/netfs/direct_write.c-321- * @iocb: IO state structure\n--\nfs/netfs/direct_write.c-331- */\nfs/netfs/direct_write.c:332:ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from)\nfs/netfs/direct_write.c-333-{\n--\nfs/netfs/direct_write.c-399-\t\t\t FSCACHE_INVAL_DIO_WRITE);\nfs/netfs/direct_write.c:400:\tret = netfs_unbuffered_write_iter_locked(iocb, from, NULL);\nfs/netfs/direct_write.c-401-out:\n--\nfs/netfs/direct_write.c-404-}\nfs/netfs/direct_write.c:405:EXPORT_SYMBOL(netfs_unbuffered_write_iter);\n--\nfs/smb/client/file.c=3096=ssize_t cifs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)\n--\nfs/smb/client/file.c-3103-\tif (iocb-\u003eki_filp-\u003ef_flags \u0026 O_DIRECT) {\nfs/smb/client/file.c:3104:\t\twritten = netfs_unbuffered_write_iter(iocb, from);\nfs/smb/client/file.c-3105-\t\tcifs_update_i_blocks_after_write(iocb, written);\n--\nfs/smb/client/file.c=3444=static void cifs_swap_submit_write(struct swap_io_ctx *ctx)\n--\nfs/smb/client/file.c-3450-\tswap_fs_prepare_rw(ctx, WRITE, \u0026iter);\nfs/smb/client/file.c:3451:\tret = netfs_unbuffered_write_iter_locked(\u0026sio-\u003eiocb, \u0026iter, NULL);\nfs/smb/client/file.c-3452-\tif (ret != -EIOCBQUEUED)\n--\ninclude/linux/netfs.h=394=ssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *from,\ninclude/linux/netfs.h-395-\t\t\t\t\t struct netfs_group *netfs_group);\ninclude/linux/netfs.h:396:ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from);\ninclude/linux/netfs.h:397:ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *iter,\ninclude/linux/netfs.h-398-\t\t\t\t\t struct netfs_group *netfs_group);\n"
} |
| 9/2 | 2026/09/24 01:08 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 12448 output: 26 thoughts: 18 Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience: **Kconfig Review - Network Filesystems** Alright, time to get down to brass tacks. I'm going to quickly run through the Kconfig files. Specifically, I need to confirm the state and configuration options related to `netfs`, the `smb client`, and `9p`. I'm mentally checking for: * The availability of these options – are they even defined within the current build environment? * Their dependencies – what other components *must* be enabled or configured for these to work correctly? Are those dependencies still sound? * Any default settings – have any relevant defaults changed recently? Are these still appropriate? And are these reasonable defaults given common use cases? * Any symbol overrides or conditional inclusions I need to be aware of. * Are there any obvious conflicts, or things that look like they will cause issues down the line. I'll be looking for any indications of recent changes, bug fixes, or enhancements related to these filesystems. I want to quickly gauge whether they are still fully supported and if any new features or capabilities have been added. This is a critical first step, as knowing the current configuration helps to inform further steps. I'm also going to see if any recent changes have caused regressions in these areas. |
| 10/2 | 2026/09/24 01:08 | tool | grepper |
0mArgs:{
"Expression": "NETFS_SUPPORT",
"PathPrefix": "fs/"
}Results: {
"Output": "fs/9p/Kconfig=2=config 9P_FS\n--\nfs/9p/Kconfig-4-\tdepends on NET_9P\nfs/9p/Kconfig:5:\tselect NETFS_SUPPORT\nfs/9p/Kconfig-6-\thelp\n--\nfs/Makefile=61=obj-$(CONFIG_DLM)\t\t+= dlm/\n--\nfs/Makefile-63-# Do not add any filesystems before this line\nfs/Makefile:64:obj-$(CONFIG_NETFS_SUPPORT)\t+= netfs/\nfs/Makefile-65-obj-$(CONFIG_EXT4_FS)\t\t+= ext4/\n--\nfs/afs/Kconfig=2=config AFS_FS\n--\nfs/afs/Kconfig-6-\tselect DNS_RESOLVER\nfs/afs/Kconfig:7:\tselect NETFS_SUPPORT\nfs/afs/Kconfig-8-\tselect CRYPTO_KRB5\n--\nfs/cachefiles/Kconfig=3=config CACHEFILES\nfs/cachefiles/Kconfig-4-\ttristate \"Filesystem caching on files\"\nfs/cachefiles/Kconfig:5:\tdepends on NETFS_SUPPORT \u0026\u0026 FSCACHE \u0026\u0026 BLOCK\nfs/cachefiles/Kconfig-6-\thelp\n--\nfs/ceph/Kconfig=2=config CEPH_FS\n--\nfs/ceph/Kconfig-5-\tselect CEPH_LIB\nfs/ceph/Kconfig:6:\tselect NETFS_SUPPORT\nfs/ceph/Kconfig-7-\tselect FS_ENCRYPTION_ALGS if FS_ENCRYPTION\n--\nfs/netfs/Kconfig-2-\nfs/netfs/Kconfig:3:config NETFS_SUPPORT\nfs/netfs/Kconfig-4-\ttristate\n--\nfs/netfs/Kconfig=10=config NETFS_STATS\nfs/netfs/Kconfig-11-\tbool \"Gather statistical information on local caching\"\nfs/netfs/Kconfig:12:\tdepends on NETFS_SUPPORT \u0026\u0026 PROC_FS\nfs/netfs/Kconfig-13-\thelp\n--\nfs/netfs/Kconfig=25=config NETFS_DEBUG\nfs/netfs/Kconfig-26-\tbool \"Enable dynamic debugging netfslib and FS-Cache\"\nfs/netfs/Kconfig:27:\tdepends on NETFS_SUPPORT\nfs/netfs/Kconfig-28-\thelp\n--\nfs/netfs/Kconfig=33=config FSCACHE\nfs/netfs/Kconfig-34-\tbool \"General filesystem local caching manager\"\nfs/netfs/Kconfig:35:\tdepends on NETFS_SUPPORT\nfs/netfs/Kconfig-36-\thelp\n--\nfs/netfs/Makefile=34=netfs-$(CONFIG_FSCACHE_STATS) += fscache_stats.o\nfs/netfs/Makefile-35-\nfs/netfs/Makefile:36:obj-$(CONFIG_NETFS_SUPPORT) += netfs.o\n--\nfs/nfs/Kconfig=173=config NFS_FSCACHE\n--\nfs/nfs/Kconfig-175-\tdepends on NFS_FS\nfs/nfs/Kconfig:176:\tselect NETFS_SUPPORT\nfs/nfs/Kconfig-177-\tselect FSCACHE\n--\nfs/smb/client/Kconfig=2=config CIFS\n--\nfs/smb/client/Kconfig-20-\tselect OID_REGISTRY\nfs/smb/client/Kconfig:21:\tselect NETFS_SUPPORT\nfs/smb/client/Kconfig-22-\thelp\n"
} |
| 11/2 | 2026/09/24 01:08 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 13659 output: 32 thoughts: 37 Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience: **Examining the Netfs Makefile for Object Compilation** Right, time to dig into the compilation process for `misc.o`, `buffered_write.o`, and `direct_write.o`. My initial instinct is to go straight to `fs/netfs/Makefile`. It's where I expect to find the rules and dependencies dictating how those specific object files are generated for the network filesystem. I'm especially interested in whether they are compiled with specific flags or in a particular way that might give clues about their performance characteristics. Is there anything unusual about their build process in comparison to other modules within `netfs`? Are they included as part of an overall "netfs" compilation rule, or do they have their own specific set of directives? I need to understand this to determine whether this build process introduces any optimizations for these files. |
| 12/2 | 2026/09/24 01:08 | tool | read-file |
0mArgs:{
"File": "fs/netfs/Makefile",
"FirstLine": 1,
"LineCount": 40
}Results: {
"Contents": " 1:\t# SPDX-License-Identifier: GPL-2.0\n 2:\t\n 3:\tnetfs-y := \\\n 4:\t\tbuffered_read.o \\\n 5:\t\tbuffered_write.o \\\n 6:\t\tdirect_read.o \\\n 7:\t\tdirect_write.o \\\n 8:\t\titerator.o \\\n 9:\t\tlocking.o \\\n 10:\t\tmain.o \\\n 11:\t\tmisc.o \\\n 12:\t\tobjects.o \\\n 13:\t\tread_collect.o \\\n 14:\t\tread_pgpriv2.o \\\n 15:\t\tread_retry.o \\\n 16:\t\tread_single.o \\\n 17:\t\trolling_buffer.o \\\n 18:\t\twrite_collect.o \\\n 19:\t\twrite_issue.o \\\n 20:\t\twrite_retry.o\n 21:\t\n 22:\tnetfs-$(CONFIG_NETFS_STATS) += stats.o\n 23:\t\n 24:\tnetfs-$(CONFIG_FSCACHE) += \\\n 25:\t\tfscache_cache.o \\\n 26:\t\tfscache_cookie.o \\\n 27:\t\tfscache_io.o \\\n 28:\t\tfscache_main.o \\\n 29:\t\tfscache_volume.o\n 30:\t\n 31:\tifeq ($(CONFIG_PROC_FS),y)\n 32:\tnetfs-$(CONFIG_FSCACHE) += fscache_proc.o\n 33:\tendif\n 34:\tnetfs-$(CONFIG_FSCACHE_STATS) += fscache_stats.o\n 35:\t\n 36:\tobj-$(CONFIG_NETFS_SUPPORT) += netfs.o\n"
} |
| 13/2 | 2026/09/24 01:08 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 14380 output: 36 thoughts: 2858 Thoughts: **Analysis of Filesystem Write Operations and Fuzzing Potential** Okay, so I've been looking at this patch and tracing how it interacts with different filesystems. I've noted that `netfs-y` includes some key files: `buffered_write.o`, `direct_write.o`, and `misc.o`, which are compiled when `CONFIG_NETFS_SUPPORT` is enabled. CIFS, using the SMB client, is also relevant here (`CONFIG_CIFS`). The question is, can we fuzz CIFS or 9p? I think we can. I've zeroed in on the `netfs_clear_stale_post_eof` function. It's called from both `netfs_buffered_write_iter_locked` and `netfs_unbuffered_write_iter`, which are used by 9p (`CONFIG_9P_FS`, `CONFIG_NET_9P`) when `v9fs_file_write_iter` is used. Furthermore, it's also called by `cifs_setsize`, `cifs_remap_file_range`, `cifs_file_copychunk_range` and `smb3_zero_range` in the CIFS code. I can see that `netfs_clear_stale_post_eof` manipulates the pagecache, specifically folios. It calls `__filemap_get_folio`, cleans page table mappings with `folio_mkclean`, marks the folio dirty with `folio_mark_dirty`, and potentially zeroes segments with `folio_zero_segment`. This function is executed when a write extends a file beyond the current `i_size` in buffered or unbuffered write operations, such as writes past the end of a file or during truncation, setsize, fallocate or copy/remap file range operations. So, could syzkaller reach these paths? Yes, syzkaller regularly tests 9p, which can be mounted via virtio (9pnet_virtio) or trans=fd using socketpairs. And it also fuzzes CIFS through loopback, sockets or SMB server. Ceph, AFS, and cachefiles are also potentially relevant, as they use netfs. The "WorthFuzzing" analysis looks promising. The modifications here don't fall under any of the negative criteria (unreachable hardware, etc.). This patch *touches* reachable executable code, it's modifying core filesystem code and page cache code that is handling writes, truncates, fallocate and remapping operations. It's working with folios, folio locking, `folio_mkclean`, and `folio_zero_segment`. This increases the probability of finding race conditions or locking bugs. Focusing on the symbols, I've identified the following: * `netfs_clear_stale_post_eof` (new function) * `netfs_buffered_write_iter_locked` * `netfs_unbuffered_write_iter` * `cifs_setsize` * `cifs_remap_file_range` * `cifs_file_copychunk_range` * `smb3_zero_range` `netfs_buffered_write_iter_locked` and `netfs_unbuffered_write_iter`, `cifs_setsize`, and `netfs_clear_stale_post_eof` are exported. The others are static. `netfs_clear_stale_post_eof` is definitely a key focus. Therefore, the patch looks like it has a high potential for fuzzing. |
| 14/2 | 2026/09/24 01:08 | tool | grepper |
0mArgs:{
"Expression": "cifs_remap_file_range",
"PathPrefix": "fs/smb/client/"
}Results: {
"Output": "fs/smb/client/cifsfs.c=1348=static int cifs_flush_folio(struct inode *inode, loff_t pos, loff_t *_fstart, loff_t *_fend,\n--\nfs/smb/client/cifsfs.c-1374-\nfs/smb/client/cifsfs.c:1375:static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,\nfs/smb/client/cifsfs.c-1376-\t\tstruct file *dst_file, loff_t destoff, loff_t len,\n--\nfs/smb/client/cifsfs.c=1674=const struct file_operations cifs_file_ops = {\n--\nfs/smb/client/cifsfs.c-1688-\t.copy_file_range = cifs_copy_file_range,\nfs/smb/client/cifsfs.c:1689:\t.remap_file_range = cifs_remap_file_range,\nfs/smb/client/cifsfs.c-1690-\t.setlease = cifs_setlease,\n--\nfs/smb/client/cifsfs.c=1694=const struct file_operations cifs_file_strict_ops = {\n--\nfs/smb/client/cifsfs.c-1708-\t.copy_file_range = cifs_copy_file_range,\nfs/smb/client/cifsfs.c:1709:\t.remap_file_range = cifs_remap_file_range,\nfs/smb/client/cifsfs.c-1710-\t.setlease = cifs_setlease,\n--\nfs/smb/client/cifsfs.c=1714=const struct file_operations cifs_file_direct_ops = {\n--\nfs/smb/client/cifsfs.c-1727-\t.copy_file_range = cifs_copy_file_range,\nfs/smb/client/cifsfs.c:1728:\t.remap_file_range = cifs_remap_file_range,\nfs/smb/client/cifsfs.c-1729-\t.llseek = cifs_llseek,\n--\nfs/smb/client/cifsfs.c=1734=const struct file_operations cifs_file_nobrl_ops = {\n--\nfs/smb/client/cifsfs.c-1746-\t.copy_file_range = cifs_copy_file_range,\nfs/smb/client/cifsfs.c:1747:\t.remap_file_range = cifs_remap_file_range,\nfs/smb/client/cifsfs.c-1748-\t.setlease = cifs_setlease,\n--\nfs/smb/client/cifsfs.c=1752=const struct file_operations cifs_file_strict_nobrl_ops = {\n--\nfs/smb/client/cifsfs.c-1764-\t.copy_file_range = cifs_copy_file_range,\nfs/smb/client/cifsfs.c:1765:\t.remap_file_range = cifs_remap_file_range,\nfs/smb/client/cifsfs.c-1766-\t.setlease = cifs_setlease,\n--\nfs/smb/client/cifsfs.c=1770=const struct file_operations cifs_file_direct_nobrl_ops = {\n--\nfs/smb/client/cifsfs.c-1781-\t.copy_file_range = cifs_copy_file_range,\nfs/smb/client/cifsfs.c:1782:\t.remap_file_range = cifs_remap_file_range,\nfs/smb/client/cifsfs.c-1783-\t.llseek = cifs_llseek,\n--\nfs/smb/client/cifsfs.c=1788=const struct file_operations cifs_dir_ops = {\n--\nfs/smb/client/cifsfs.c-1793-\t.copy_file_range = cifs_copy_file_range,\nfs/smb/client/cifsfs.c:1794:\t.remap_file_range = cifs_remap_file_range,\nfs/smb/client/cifsfs.c-1795-\t.llseek = generic_file_llseek,\n"
} |
| 15/2 | 2026/09/24 01:08 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 19230 output: 34 thoughts: 83 Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience and presented in the first person: **Analyzing the `cifs_remap_file_range` Function** Alright, even if we assume `cifs_remap_file_range` is statically defined, it's still a non-inlined function within `fs/smb/client/cifsfs.c`. Because it's ultimately assigned to a function pointer within `cifs_file_ops`, it has a corresponding symbol that will inevitably appear in `kallsyms`. We need to be able to identify it. Now, let's turn our attention to `smb3_zero_range`. Let's see what's going on there. |
| 16/2 | 2026/09/24 01:08 | tool | grepper |
0mArgs:{
"Expression": "smb3_zero_range",
"PathPrefix": "fs/smb/client/"
}Results: {
"Output": "fs/smb/client/smb2ops.c=3505=static long smb3_zero_data(struct file *file, struct cifs_tcon *tcon,\n--\nfs/smb/client/smb2ops.c-3522-\nfs/smb/client/smb2ops.c:3523:static long smb3_zero_range(struct file *file, struct cifs_tcon *tcon,\nfs/smb/client/smb2ops.c-3524-\t\t\t unsigned long long offset, unsigned long long len,\n--\nfs/smb/client/smb2ops.c=4335=static long smb3_fallocate(struct file *file, struct cifs_tcon *tcon, int mode,\n--\nfs/smb/client/smb2ops.c-4342-\t\tif (mode \u0026 FALLOC_FL_KEEP_SIZE)\nfs/smb/client/smb2ops.c:4343:\t\t\treturn smb3_zero_range(file, tcon, off, len, true);\nfs/smb/client/smb2ops.c:4344:\t\treturn smb3_zero_range(file, tcon, off, len, false);\nfs/smb/client/smb2ops.c-4345-\t} else if (mode == FALLOC_FL_KEEP_SIZE)\n"
} |
| 17/2 | 2026/09/24 01:08 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 19867 output: 33 thoughts: 85 Thoughts: Okay, let's break this down. **Configuration Checkpoint** Right, I need to verify the configuration requirements for compiling and running this code, specifically concerning `fs/netfs`. First stop, the `fs/netfs/Kconfig` file. Hmm, there's `config NETFS_SUPPORT`, set as a tristate. Now the question is, is this a user-selectable option, or is it implicitly selected by other filesystems? Need to double-check that Kconfig file and its dependencies to be certain. Let me go back and re-examine the `fs/netfs/Kconfig` file. |
| 18/2 | 2026/09/24 01:08 | tool | read-file |
0mArgs:{
"File": "fs/netfs/Kconfig",
"FirstLine": 1,
"LineCount": 40
}Results: {
"Contents": " 1:\t# SPDX-License-Identifier: GPL-2.0-only\n 2:\t\n 3:\tconfig NETFS_SUPPORT\n 4:\t\ttristate\n 5:\t\thelp\n 6:\t\t This option enables support for network filesystems, including\n 7:\t\t helpers for high-level buffered I/O, abstracting out read\n 8:\t\t segmentation, local caching and transparent huge page support.\n 9:\t\n 10:\tconfig NETFS_STATS\n 11:\t\tbool \"Gather statistical information on local caching\"\n 12:\t\tdepends on NETFS_SUPPORT \u0026\u0026 PROC_FS\n 13:\t\thelp\n 14:\t\t This option causes statistical information to be gathered on local\n 15:\t\t caching and exported through file:\n 16:\t\n 17:\t\t\t/proc/fs/fscache/stats\n 18:\t\n 19:\t\t The gathering of statistics adds a certain amount of overhead to\n 20:\t\t execution as there are a quite a few stats gathered, and on a\n 21:\t\t multi-CPU system these may be on cachelines that keep bouncing\n 22:\t\t between CPUs. On the other hand, the stats are very useful for\n 23:\t\t debugging purposes. Saying 'Y' here is recommended.\n 24:\t\n 25:\tconfig NETFS_DEBUG\n 26:\t\tbool \"Enable dynamic debugging netfslib and FS-Cache\"\n 27:\t\tdepends on NETFS_SUPPORT\n 28:\t\thelp\n 29:\t\t This permits debugging to be dynamically enabled in the local caching\n 30:\t\t management module. If this is set, the debugging output may be\n 31:\t\t enabled by setting bits in /sys/module/netfs/parameters/debug.\n 32:\t\n 33:\tconfig FSCACHE\n 34:\t\tbool \"General filesystem local caching manager\"\n 35:\t\tdepends on NETFS_SUPPORT\n 36:\t\thelp\n 37:\t\t This option enables a generic filesystem caching manager that can be\n 38:\t\t used by various network and other filesystems to cache data locally.\n 39:\t\t Different sorts of caches can be plugged in, depending on the\n 40:\t\t resources available.\n"
} |
| 19/2 | 2026/09/24 01:08 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 20680 output: 35 thoughts: 114 Thoughts: **My Analysis of NETFS_SUPPORT Dependencies** Okay, so I see that `NETFS_SUPPORT` is a pretty fundamental option, obviously. It looks like several network filesystems depend on it: `CIFS`, `9P_FS`, `AFS_FS`, `CEPH_FS`, and even `NFS_FSCACHE`. That's a diverse group, which suggests `NETFS_SUPPORT` provides some core functionality that these filesystems all leverage in their network interactions. Now, let's drill down a bit. `CIFS` is particularly interesting as a common SMB client, so it makes sense to confirm its dependencies. I'm going to quickly check `fs/smb/client/Kconfig` to confirm any specific relationships and to see what other options are involved in its configuration. Understanding `CIFS`'s needs might illuminate the broader role of `NETFS_SUPPORT`. |
| 20/2 | 2026/09/24 01:08 | tool | read-file |
0mArgs:{
"File": "fs/smb/client/Kconfig",
"FirstLine": 1,
"LineCount": 40
}Results: {
"Contents": " 1:\t# SPDX-License-Identifier: GPL-2.0-only\n 2:\tconfig CIFS\n 3:\t\ttristate \"SMB3 and CIFS support (advanced network filesystem)\"\n 4:\t\tdepends on INET\n 5:\t\tselect NLS\n 6:\t\tselect NLS_UCS2_UTILS\n 7:\t\tselect CRYPTO\n 8:\t\tselect CRYPTO_AEAD2\n 9:\t\tselect CRYPTO_CCM\n 10:\t\tselect CRYPTO_GCM\n 11:\t\tselect CRYPTO_AES\n 12:\t\tselect CRYPTO_LIB_AES_CBC_MACS\n 13:\t\tselect CRYPTO_LIB_ARC4\n 14:\t\tselect CRYPTO_LIB_MD5\n 15:\t\tselect CRYPTO_LIB_SHA256\n 16:\t\tselect CRYPTO_LIB_SHA512\n 17:\t\tselect KEYS\n 18:\t\tselect DNS_RESOLVER\n 19:\t\tselect ASN1\n 20:\t\tselect OID_REGISTRY\n 21:\t\tselect NETFS_SUPPORT\n 22:\t\thelp\n 23:\t\t This is the client VFS module for the SMB3 family of network file\n 24:\t\t protocols (including the most recent, most secure dialect SMB3.1.1).\n 25:\t\t This module also includes support for earlier dialects such as\n 26:\t\t SMB2.1, SMB2 and even the old Common Internet File System (CIFS)\n 27:\t\t protocol. CIFS was the successor to the original network filesystem\n 28:\t\t protocol, Server Message Block (SMB ie SMB1), the native file sharing\n 29:\t\t mechanism for most early PC operating systems.\n 30:\t\n 31:\t\t The SMB3.1.1 protocol is supported by most modern operating systems\n 32:\t\t and NAS appliances (e.g. Samba, Windows 11, Windows Server 2022,\n 33:\t\t MacOS) and even in the cloud (e.g. Microsoft Azure) and also by the\n 34:\t\t Linux kernel server, ksmbd. Support for the older CIFS protocol was\n 35:\t\t included in Windows NT4, 2000 and XP (and later). Use of dialects\n 36:\t\t older than SMB2.1 is often discouraged on public networks.\n 37:\t\t This module also provides limited support for OS/2 and Windows ME\n 38:\t\t and similar very old servers.\n 39:\t\n 40:\t\t This module provides an advanced network file system client for\n"
} |
| 21/2 | 2026/09/24 01:08 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 21657 output: 33 thoughts: 30 Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience: **Kernel Filesystem Dependencies: A Quick Mental Audit** Right, so I'm thinking about CIFS, and it's practically hardwired in my mind that it sits on top of `INET`. That dependency is almost instinctual at this point, but I'm trying to be thorough, especially when reviewing filesystem internals. What about `9P_FS`? It's been a while since I've dived deep into that code, and I need to solidify my understanding. I should probably brush up on it, and the best starting point is always the Kconfig. Let's see how `fs/9p/Kconfig` is configured. I'm going to quickly check that now. |
| 22/2 | 2026/09/24 01:08 | tool | read-file |
0mArgs:{
"File": "fs/9p/Kconfig",
"FirstLine": 1,
"LineCount": 30
}Results: {
"Contents": " 1:\t# SPDX-License-Identifier: GPL-2.0-only\n 2:\tconfig 9P_FS\n 3:\t\ttristate \"Plan 9 Resource Sharing Support (9P2000)\"\n 4:\t\tdepends on NET_9P\n 5:\t\tselect NETFS_SUPPORT\n 6:\t\thelp\n 7:\t\t If you say Y here, you will get experimental support for\n 8:\t\t Plan 9 resource sharing via the 9P2000 protocol.\n 9:\t\n 10:\t\t See \u003chttp://v9fs.sf.net\u003e for more information.\n 11:\t\n 12:\t\t If unsure, say N.\n 13:\t\n 14:\tif 9P_FS\n 15:\tconfig 9P_FSCACHE\n 16:\t\tbool \"Enable 9P client caching support\"\n 17:\t\tdepends on 9P_FS=m \u0026\u0026 FSCACHE || 9P_FS=y \u0026\u0026 FSCACHE=y\n 18:\t\thelp\n 19:\t\t Choose Y here to enable persistent, read-only local\n 20:\t\t caching support for 9p clients using FS-Cache\n 21:\t\n 22:\t\n 23:\tconfig 9P_FS_POSIX_ACL\n 24:\t\tbool \"9P POSIX Access Control Lists\"\n 25:\t\tselect FS_POSIX_ACL\n 26:\t\thelp\n 27:\t\t POSIX Access Control Lists (ACLs) support permissions for users and\n 28:\t\t groups beyond the owner/group/world scheme.\n 29:\t\n 30:\t\t If you don't know what Access Control Lists are, say N\n"
} |
| 23/2 | 2026/09/24 01:08 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 22316 output: 34 thoughts: 171 Thoughts: **My Configuration Considerations** Okay, so I'm diving into these kernel configurations. Enabling `NETFS_SUPPORT` and `CIFS` directly should bring in both the core network filesystem support and the specific CIFS modifications. I need to be sure about this, so can `CONFIG_NETFS_SUPPORT` really be enabled directly? It's `tristate` and doesn't have a prompt, so it has to be either selected or set through other config options. Alright, these are the configs that need attention: `NETFS_SUPPORT`, `CIFS`, `9P_FS`, and `NET_9P`. Now, let's look at `CIFS`. I need to ensure that it doesn't depend on any *other* specific configurations to compile those modified files, specifically `fs/smb/client/cifsfs.c`, `fs/smb/client/inode.c`, and `fs/smb/client/smb2ops.c`. A quick check of `fs/smb/client/Makefile` will probably clear things up. |
| 24/2 | 2026/09/24 01:08 | tool | read-file |
0mArgs:{
"File": "fs/smb/client/Makefile",
"FirstLine": 1,
"LineCount": 40
}Results: {
"Contents": " 1:\t# SPDX-License-Identifier: GPL-2.0\n 2:\t#\n 3:\t# Makefile for Linux CIFS/SMB2/SMB3 VFS client\n 4:\t#\n 5:\tccflags-y += -I$(src)\t\t# needed for trace events\n 6:\tobj-$(CONFIG_CIFS) += cifs.o\n 7:\t\n 8:\tcifs-y := trace.o cifsfs.o cifs_debug.o connect.o dir.o file.o \\\n 9:\t\t inode.o link.o misc.o netmisc.o smbencrypt.o transport.o \\\n 10:\t\t cached_dir.o cifs_unicode.o cifsencrypt.o \\\n 11:\t\t readdir.o ioctl.o sess.o export.o unc.o winucase.o \\\n 12:\t\t smb2ops.o smb2maperror.o smb2transport.o \\\n 13:\t\t smb2misc.o smb2pdu.o smb2inode.o smb2file.o cifsacl.o fs_context.o \\\n 14:\t\t dns_resolve.o cifs_spnego_negtokeninit.asn1.o asn1.o \\\n 15:\t\t namespace.o reparse.o\n 16:\t\n 17:\t$(obj)/asn1.o: $(obj)/cifs_spnego_negtokeninit.asn1.h\n 18:\t\n 19:\t$(obj)/cifs_spnego_negtokeninit.asn1.o: $(obj)/cifs_spnego_negtokeninit.asn1.c $(obj)/cifs_spnego_negtokeninit.asn1.h\n 20:\t\n 21:\tcifs-$(CONFIG_CIFS_XATTR) += xattr.o\n 22:\t\n 23:\tcifs-$(CONFIG_CIFS_UPCALL) += cifs_spnego.o\n 24:\t\n 25:\tcifs-$(CONFIG_CIFS_DFS_UPCALL) += dfs_cache.o dfs.o\n 26:\t\n 27:\tcifs-$(CONFIG_CIFS_SWN_UPCALL) += netlink.o cifs_swn.o\n 28:\t\n 29:\tcifs-$(CONFIG_CIFS_FSCACHE) += fscache.o\n 30:\t\n 31:\tcifs-$(CONFIG_CIFS_SMB_DIRECT) += smbdirect.o\n 32:\t\n 33:\tcifs-$(CONFIG_CIFS_ROOT) += cifsroot.o\n 34:\t\n 35:\tcifs-$(CONFIG_CIFS_ALLOW_INSECURE_LEGACY) += \\\n 36:\t\tcifssmb.o \\\n 37:\t\tsmb1debug.o \\\n 38:\t\tsmb1encrypt.o \\\n 39:\t\tsmb1maperror.o \\\n 40:\t\tsmb1misc.o \\\n"
} |
| 25/2 | 2026/09/24 01:08 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 23513 output: 262 thoughts: 636 Thoughts: **Reviewing the Implementation of `netfs_clear_stale_post_eof` and Associated Changes** Okay, let's break this down. From what I can see, `cifsfs.o`, `inode.o`, and `smb2ops.o` are all directly enabled by `CONFIG_CIFS`, which seems logical given their function. Importantly, `CONFIG_CIFS` also selects `NETFS_SUPPORT`, which is the core dependency here. `CONFIG_9P_FS` with `CONFIG_NET_9P` also select `NETFS_SUPPORT`. My focus is on the impact of `netfs_clear_stale_post_eof`, which is the new function that zeros out stale data past the end-of-file (EOF) in pagecache folios. I've tracked the modifications: * `netfs_buffered_write_iter_locked` is modified to call it when extending a file beyond EOF. * `netfs_unbuffered_write_iter` similarly calls `netfs_clear_stale_post_eof` on EOF extension. * `cifs_setsize`, CIFS's truncate/setsize handler, is modified to call it too. * `cifs_remap_file_range` and `cifs_file_copychunk_range` from the CIFS side are modified to invalidate/truncate pagecache starting at the old EOF. * Finally, `smb3_zero_range` in CIFS, is modified to truncate pagecache starting at the old EOF as well. I need to confirm these functions are unique to netfs and cifs. Let me check the diff again to confirm: * `Documentation/filesystems/netfs_library.rst` provides the documentation. * `fs/netfs/buffered_write.c` and `fs/netfs/direct_write.c` contain the write iterator modifications. * `fs/netfs/misc.c` is the source for `netfs_clear_stale_post_eof`. * `fs/smb/client/cifsfs.c` and `fs/smb/client/inode.c` contains the CIFS functions. * `fs/smb/client/smb2ops.c` contains the function for the smb3 zero range. * `include/linux/netfs.h` provides the function prototype. Yes, they appear specific to `netfs` and CIFS write/truncate/range operations; I don't see anything universally shared. Are all of these symbols present and exported/addressable? Yes, they're all function definitions in the .c files, and that should be fine. Finally, I need to verify the required configurations: `NETFS_SUPPORT`, `CIFS`, `9P_FS`, and `NET_9P` are present and that should be sufficient. Everything checks out. I'm ready to call `set-results`. |
| 26/2 | 2026/09/24 01:08 | tool | set-results |
0mArgs:{
"EnableConfigs": [
"NETFS_SUPPORT",
"CIFS",
"9P_FS",
"NET_9P"
],
"FocusSymbols": [
"netfs_clear_stale_post_eof",
"netfs_buffered_write_iter_locked",
"netfs_unbuffered_write_iter",
"cifs_setsize",
"cifs_remap_file_range",
"cifs_file_copychunk_range",
"smb3_zero_range"
],
"Reasoning": "The patch series modifies core netfs and CIFS pagecache handling when extending files or operating on file ranges. It introduces `netfs_clear_stale_post_eof()` to clear and clean stale post-EOF pagecache folios dirtied via mmap before extending a file, and integrates it into netfs buffered/unbuffered write paths and CIFS setsize/range operations. These are reachable file operations in virtualized environments (e.g. via 9p or CIFS/SMB loopback) involving folio locking, clean/dirty state transitions, and pagecache truncation, warranting fuzzing.",
"WorthFuzzing": true
}Results: {
"EnableConfigs": [
"NETFS_SUPPORT",
"CIFS",
"9P_FS",
"NET_9P"
],
"FocusSymbols": [
"netfs_clear_stale_post_eof",
"netfs_buffered_write_iter_locked",
"netfs_unbuffered_write_iter",
"cifs_setsize",
"cifs_remap_file_range",
"cifs_file_copychunk_range",
"smb3_zero_range"
],
"Reasoning": "The patch series modifies core netfs and CIFS pagecache handling when extending files or operating on file ranges. It introduces `netfs_clear_stale_post_eof()` to clear and clean stale post-EOF pagecache folios dirtied via mmap before extending a file, and integrates it into netfs buffered/unbuffered write paths and CIFS setsize/range operations. These are reachable file operations in virtualized environments (e.g. via 9p or CIFS/SMB loopback) involving folio locking, clean/dirty state transitions, and pagecache truncation, warranting fuzzing.",
"WorthFuzzing": true
} |
| 27/1 | 2026/09/24 01:08 | action | If |
1mArgs:{
"WorthFuzzing": true
}Results: null |
| 28/2 | 2026/09/24 01:08 | agent | kmsan-evaluator |
1mModel:core Args: null Results: {
"KMSANReasoning": "The patch introduces `netfs_clear_stale_post_eof()` to zero out stale pagecache data in the post-EOF region when a file is extended, preventing dirty data written via mmap beyond the previous EOF from being exposed as file content. It also adjusts truncation and invalidation ranges in CIFS.\n\n- No uninitialized stack or heap allocations/structures are introduced or modified. All local variables (`mapping`, `fgp`, `folio`, `offset`, `end`) are fully initialized scalars.\n- No uninitialized kernel memory or struct padding is copied to user space. The data cleared in the pagecache is previously written user data (or page content) to satisfy POSIX hole-zeroing semantics, not uninitialized kernel memory.\n- Any potential bugs introduced by these changes (e.g., potential out-of-bounds indexing in `folio_zero_segment()`, locking/sleeping issues under `FGP_LOCK` or `IOCB_NOWAIT`, or NULL/ERR pointer dereferences on `folio`) are covered by standard sanitizers like KASAN and LOCKDEP.\n- There are no uninitialized memory risks that would require or benefit from a dedicated KMSAN fuzzing session.",
"NeedsKMSAN": false
}Instruction: You are an expert Linux kernel security engineer specializing in kernel memory
error detectors (KASAN and KMSAN). Your job is to review the provided patch series and
determine if the code changes justify spawning a dedicated KMSAN (KernelMemorySanitizer)
fuzzing session in addition to standard KASAN fuzzing.
CRITICAL DISTINCTION BETWEEN KASAN AND KMSAN:
- Standard KASAN kernel builds (upstream-apparmor-kasan.config) already enable
a comprehensive suite of debugging tools and sanitizers, including KASAN
(out-of-bounds accesses, use-after-free, double free, invalid free), LOCKDEP
(locking bugs and deadlocks), UB-sanitizers, and memory corruption checks.
- KMSAN (KernelMemorySanitizer) detects reads of UNINITIALIZED memory (stack, heap,
or page allocations) and kernel-to-user memory info-leaks.
Rule: THERE IS NO SENSE IN RUNNING A KMSAN SESSION IF A BUG CAN BE CAUGHT BY KASAN,
LOCKDEP, OR OTHER STANDARD BUG DETECTORS.
A dedicated KMSAN fuzzing session incurs significant resource costs. You must ONLY
set NeedsKMSAN=true if the code changes introduce or expose UNINITIALIZED MEMORY risks
that are detected ONLY by KMSAN.
Look holistically at the patch series and surrounding code. Even if no direct
uninitialized field accesses or new buffer allocations are added in the diff itself,
a patch may alter control flow, bounds checking, or data length calculations in ways
that change how the rest of the code operates on existing buffers (e.g. allowing
uninitialized stack/heap memory to be read, copied to user space, or used in control
flow). Do not hesitate to use your code access tools to inspect the surrounding code,
called functions, and callers.
Set NeedsKMSAN=true ONLY IF the patch introduces or modifies:
1. Kernel structures sent to user space (via copy_to_user, put_user, netlink skb
attributes, ioctl output arguments, socket options, or BPF buffers) where fields
or structure padding might not be fully initialized/zeroed.
2. Conditional logic or branching that depends on potentially uninitialized variables
or struct fields.
3. Allocation or initialization of complex data structures where uninitialized fields
could be read later in reachable code paths.
4. Bounds checks, lengths, or logic in a way that allows surrounding code to access
uninitialized bytes of existing buffers.
Set NeedsKMSAN=false IF:
- The code changes primarily risk out-of-bounds access, array overflows, NULL pointer
dereferences, locking deadlocks, or use-after-free bugs (these are already caught
by KASAN, LOCKDEP, or standard bug detectors).
- All stack/heap structures touched or introduced by the patch are fully zeroed
or initialized (e.g. using = {0}, memset, kzalloc) before being read or copied.
- The patch does not introduce any risk of uninitialized memory usage or info-leaks.
Use your code access tools to inspect the surrounding code if necessary, then provide
detailed KMSANReasoning contrasting KASAN vs KMSAN applicability for this patch.
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt: Target architecture: amd64
For your convenience, here is the diff of the changes:
commit ffe5c0db81fb5e586f5ad7fe7cabab11275ed0d4
Author: syz-cluster <triage@syzkaller.com>
Date: Thu Sep 24 01:07:46 2026 +0000
syz-cluster: applied patch under review
diff --git a/Documentation/filesystems/netfs_library.rst b/Documentation/filesystems/netfs_library.rst
index ddd799df6ce36..58b0adacc2f3e 100644
--- a/Documentation/filesystems/netfs_library.rst
+++ b/Documentation/filesystems/netfs_library.rst
@@ -451,6 +451,24 @@ one.
The inode should be marked ``NETFS_ICTX_SINGLE_NO_UPLOAD`` if this API is to be
used. The writeback function requires the buffer to be of ITER_FOLIOQ type.
+Clearing Stale Post-EOF Pagecache
+---------------------------------
+
+When a file is extended, data left in the pagecache past the old EOF by a write
+through an mmap must not be exposed as file content. Netfslib clears this on
+its own write paths, and exports a helper so a filesystem can do the same from,
+for instance, its truncate or fallocate paths::
+
+ int netfs_clear_stale_post_eof(struct inode *inode, unsigned long long from,
+ unsigned long long to, bool nowait);
+
+This zeroes any such data within the ``[from, to)`` hole to be made, where @from
+is the current EOF. Only the folio straddling @from can hold data written past
+the EOF through an mmap, as pages wholly beyond the EOF can't be faulted in, so
+the zeroing is limited to that folio and clamped to the top of the hole. The
+folio is zeroed rather than dropped so that a concurrent extending write can't
+lose data. If @nowait is set, it returns ``-EAGAIN`` rather than blocking.
+
High-Level VM API
==================
diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
index 2cdb68e6b16ff..cc0561f77bd08 100644
--- a/fs/netfs/buffered_write.c
+++ b/fs/netfs/buffered_write.c
@@ -469,6 +469,7 @@ ssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *fr
struct netfs_group *netfs_group)
{
struct file *file = iocb->ki_filp;
+ struct inode *inode = file_inode(file);
ssize_t ret;
trace_netfs_write_iter(iocb, from);
@@ -481,6 +482,14 @@ ssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *fr
if (ret)
return ret;
+ if (iocb->ki_pos > i_size_read(inode)) {
+ ret = netfs_clear_stale_post_eof(inode, i_size_read(inode),
+ iocb->ki_pos,
+ iocb->ki_flags & IOCB_NOWAIT);
+ if (ret)
+ return ret;
+ }
+
return netfs_perform_write(iocb, from, netfs_group);
}
EXPORT_SYMBOL(netfs_buffered_write_iter_locked);
diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c
index 2361277416c73..36c36bc6c9d26 100644
--- a/fs/netfs/direct_write.c
+++ b/fs/netfs/direct_write.c
@@ -359,6 +359,15 @@ ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from)
ret = file_update_time(file);
if (ret < 0)
goto out;
+
+ if (iocb->ki_pos > i_size_read(inode)) {
+ ret = netfs_clear_stale_post_eof(inode, i_size_read(inode),
+ iocb->ki_pos,
+ iocb->ki_flags & IOCB_NOWAIT);
+ if (ret < 0)
+ goto out;
+ }
+
if (iocb->ki_flags & IOCB_NOWAIT) {
/* We could block if there are any pages in the range. */
ret = -EAGAIN;
diff --git a/fs/netfs/misc.c b/fs/netfs/misc.c
index f5c1c463f4ff7..b9ca24b3dfdae 100644
--- a/fs/netfs/misc.c
+++ b/fs/netfs/misc.c
@@ -6,6 +6,7 @@
*/
#include <linux/swap.h>
+#include <linux/rmap.h>
#include "internal.h"
/**
@@ -582,3 +583,53 @@ void netfs_wait_for_put_ra_refs(struct netfs_io_request *rreq)
trace_netfs_rreq(rreq, netfs_rreq_trace_waited_put_ra_refs);
finish_wait(&rreq->waitq, &myself);
}
+
+/**
+ * netfs_clear_stale_post_eof - Clear stale pagecache in a to-be-created hole
+ * @inode: The inode to act upon.
+ * @from: The base of the hole to be made (the current EOF).
+ * @to: The top of the hole to be made.
+ * @nowait: True to return -EAGAIN rather than block.
+ *
+ * Before extending a file, zero any data left in the pagecache within the
+ * [@from, @to) hole by a write through an mmap so that it isn't exposed as file
+ * content once the file is extended. Only the uptodate folio straddling @from
+ * can hold such data as pages wholly beyond the EOF can't be faulted in, so the
+ * zeroing is limited to that folio. The folio is zeroed rather than dropped so
+ * that a concurrent extending write can't lose data.
+ *
+ * Return: 0 on success, or -EAGAIN if @nowait is set and the folio would need
+ * to be waited on.
+ */
+int netfs_clear_stale_post_eof(struct inode *inode, unsigned long long from,
+ unsigned long long to, bool nowait)
+{
+ struct address_space *mapping = inode->i_mapping;
+ fgf_t fgp = FGP_LOCK;
+ struct folio *folio;
+
+ if (from >= to)
+ return 0;
+
+ if (nowait)
+ fgp |= FGP_NOWAIT;
+
+ folio = __filemap_get_folio(mapping, from >> PAGE_SHIFT, fgp, 0);
+ if (IS_ERR(folio))
+ return PTR_ERR(folio) == -EAGAIN ? -EAGAIN : 0;
+
+ if (folio_mkclean(folio))
+ folio_mark_dirty(folio);
+
+ if (folio_test_uptodate(folio)) {
+ size_t end = umin(to - folio_pos(folio), folio_size(folio));
+ size_t offset = offset_in_folio(folio, from);
+
+ folio_zero_segment(folio, offset, end);
+ }
+
+ folio_unlock(folio);
+ folio_put(folio);
+ return 0;
+}
+EXPORT_SYMBOL(netfs_clear_stale_post_eof);
diff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c
index 7ecd70efdfea8..6410249f529a2 100644
--- a/fs/smb/client/cifsfs.c
+++ b/fs/smb/client/cifsfs.c
@@ -1467,9 +1467,14 @@ static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,
i_size = target_inode->i_size;
spin_unlock(&target_inode->i_lock);
- /* Discard all the folios that overlap the destination region. */
+ /*
+ * Discard all the folios that overlap the destination region. Start at
+ * the old EOF when extending so the folio straddling it, which may hold
+ * data written past EOF through an mmap, is dropped too.
+ */
cifs_dbg(FYI, "about to discard pages %llx-%llx\n", fstart, fend);
- truncate_inode_pages_range(&target_inode->i_data, fstart, fend);
+ truncate_inode_pages_range(&target_inode->i_data,
+ min(fstart, i_size), fend);
fscache_invalidate(cifs_inode_cookie(target_inode), NULL, i_size, 0);
@@ -1581,8 +1586,13 @@ ssize_t cifs_file_copychunk_range(unsigned int xid,
/* Flush and invalidate all the folios in the destination region. If
* the copy was successful, then some of the flush is extra overhead,
* but we need to allow for the copy failing in some way (eg. ENOSPC).
+ *
+ * Start at the old EOF when extending so the folio straddling it, which
+ * may hold data written past EOF through an mmap, is dropped too.
*/
- rc = filemap_invalidate_inode(target_inode, true, destoff, destoff + len - 1);
+ rc = filemap_invalidate_inode(target_inode, true,
+ min(destoff, i_size_read(target_inode)),
+ destoff + len - 1);
if (rc)
goto unlock;
diff --git a/fs/smb/client/inode.c b/fs/smb/client/inode.c
index 1fe0ef0a95dbd..9abb40f871c66 100644
--- a/fs/smb/client/inode.c
+++ b/fs/smb/client/inode.c
@@ -3071,8 +3071,16 @@ void cifs_setsize(struct inode *inode, loff_t offset)
inode->i_blocks = blocks;
spin_unlock(&inode->i_lock);
inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
+ /*
+ * When extending, zero the tail of the folio straddling the old EOF
+ * so that data dirtied past EOF through an mmap isn't exposed once the
+ * file is extended. This mirrors pagecache_isize_extended(), which
+ * can't be used here as it is a no-op when the block size is >=
+ * PAGE_SIZE, as on CIFS. truncate_pagecache() then drops the
+ * pagecache beyond the new EOF, as in truncate_setsize().
+ */
if (offset > old_size)
- pagecache_isize_extended(inode, old_size, offset);
+ netfs_clear_stale_post_eof(inode, old_size, offset, false);
truncate_pagecache(inode, offset);
netfs_wait_for_outstanding_io(inode);
}
diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index 3464470d32977..7282ed9164705 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -3558,8 +3558,11 @@ static long smb3_zero_range(struct file *file, struct cifs_tcon *tcon,
/*
* We zero the range through ioctl, so we need remove the page caches
* first, otherwise the data may be inconsistent with the server.
+ *
+ * Start at the old EOF when extending so the folio straddling it, which
+ * may hold data written past EOF through an mmap, is dropped too.
*/
- truncate_pagecache_range(inode, offset, offset + len - 1);
+ truncate_pagecache_range(inode, min(offset, i_size), offset + len - 1);
netfs_wait_for_outstanding_io(inode);
/* if file not oplocked can't be sure whether asking to extend size */
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index b4dd32863dd45..2981290b9a77a 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -397,6 +397,8 @@ ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from);
ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *iter,
struct netfs_group *netfs_group);
ssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from);
+int netfs_clear_stale_post_eof(struct inode *inode, unsigned long long from,
+ unsigned long long to, bool nowait);
/* Single, monolithic object read/write API. */
void netfs_single_mark_inode_dirty(struct inode *inode);
|
| 29/3 | 2026/09/24 01:08 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 5429 output: 22 thoughts: 1290 Thoughts: **KMSAN Assessment: Stale Pagecache Data in netfs and cifs** Okay, let's break this down. The patch is addressing the potential exposure of stale pagecache data in `netfs` and `cifs` when a file is extended after writes via mmap. Specifically, the concern is that if a file grows, data cached beyond the original EOF (End Of File) might incorrectly become part of the file content. `netfs` already handles this in its write paths and exposes a helper function, `netfs_clear_stale_post_eof`, to clear this stale data. This is called in buffered and unbuffered write iterations, as well as `cifs_setsize`. Additionally, `cifsfs.c` and `smb2ops.c` now have page cache invalidation ranges that start at `min(offset, i_size)`. My initial thought is, does this even warrant a KMSAN check? KMSAN is for detecting reads of *uninitialized* memory, whereas standard KASAN covers things like out-of-bounds access, use-after-free, etc. I need to be *sure* that the code introduces a potential for reading uninitialized memory, *and* that KASAN wouldn't catch it. Let's carefully consider the rules for KMSAN. It's a resource hog, so I only want to flag `NeedsKMSAN=true` if it's *absolutely* necessary. The core issue: data left in the pagecache past the old EOF. Is that uninitialized? Let's consider an example. A file is 100 bytes, mmaps to 4096 bytes. Then the user writes to bytes 200..300. The file is then extended to 500 bytes. With POSIX semantics, that extension *should* result in zeroes in the "holes" (301 to 500). If the pagecache contains *stale* data past the original EOF, is that *uninitialized*, or just old data that's effectively "garbage" until overwritten? Is pagecache tracked by KMSAN? My critical question: *is that stale pagecache data considered uninitialized memory from a KMSAN perspective?* Because that's the *only* reason to even think about KMSAN. KMSAN tracks kernel memory allocations: stack, kmalloc, vmalloc, page_alloc, for *kernel* structures. Does it track page cache pages that contain file data, or, more accurately, is it even tracking user pages/file data? Does KMSAN even *care* about the content of pagecache pages or user pages or file data? I need to know how KMSAN handles `struct page`, page cache, and `copy_to_user` from the page cache. I need to check how KMSAN deals with pagecache, filemap or copy_to_user from page cache to determine if the data being cleared is, in fact, relevant for KMSAN. I'll use `grepper` to search for related code paths and understand KMSAN's coverage of these areas. |
| 30/3 | 2026/09/24 01:09 | tool | grepper |
0mArgs:{
"Expression": "kmsan_copy_to_user"
}Results: {
"Output": "include/linux/instrumented.h=127=instrument_copy_to_user(void __user *to, const void *from, unsigned long n)\n--\ninclude/linux/instrumented.h-130-\tkcsan_check_read(from, n);\ninclude/linux/instrumented.h:131:\tkmsan_copy_to_user(to, from, n, 0);\ninclude/linux/instrumented.h-132-}\n--\ninclude/linux/instrumented.h=195=static __always_inline void instrument_memcpy_after(void *to, const void *from,\n--\ninclude/linux/instrumented.h-229-({\t\t\t\t\t\t\t\t\\\ninclude/linux/instrumented.h:230:\tkmsan_copy_to_user(ptr, \u0026from, sizeof(from), 0);\t\\\ninclude/linux/instrumented.h-231-})\n--\ninclude/linux/kmsan-checks.h=47=void kmsan_check_memory(const void *address, size_t size);\n--\ninclude/linux/kmsan-checks.h-49-/**\ninclude/linux/kmsan-checks.h:50: * kmsan_copy_to_user() - Notify KMSAN about a data transfer to userspace.\ninclude/linux/kmsan-checks.h-51- * @to: destination address in the userspace.\n--\ninclude/linux/kmsan-checks.h-60- */\ninclude/linux/kmsan-checks.h:61:void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,\ninclude/linux/kmsan-checks.h-62-\t\t\tsize_t left);\n--\ninclude/linux/kmsan-checks.h=84=static inline void kmsan_check_memory(const void *address, size_t size)\n--\ninclude/linux/kmsan-checks.h-86-}\ninclude/linux/kmsan-checks.h:87:static inline void kmsan_copy_to_user(void __user *to, const void *from,\ninclude/linux/kmsan-checks.h-88-\t\t\t\t size_t to_copy, size_t left)\n--\nmm/kmsan/hooks.c=220=void kmsan_iounmap_page_range(unsigned long start, unsigned long end)\n--\nmm/kmsan/hooks.c-248-\nmm/kmsan/hooks.c:249:void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,\nmm/kmsan/hooks.c-250-\t\t\tsize_t left)\n--\nmm/kmsan/hooks.c-287-}\nmm/kmsan/hooks.c:288:EXPORT_SYMBOL(kmsan_copy_to_user);\nmm/kmsan/hooks.c-289-\n--\ntools/objtool/check.c=1095=static const char *uaccess_safe_builtin[] = {\n--\ntools/objtool/check.c-1233-\t/* KMSAN */\ntools/objtool/check.c:1234:\t\"kmsan_copy_to_user\",\ntools/objtool/check.c-1235-\t\"kmsan_disable_current\",\n"
} |
| 31/3 | 2026/09/24 01:09 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 8236 output: 36 thoughts: 18 Thoughts: Here's my take on the thought process, as if it were my own: **Diving into the Hook - mm/kmsan/hooks.c:249** Okay, time to get to the root of this. Let's start with a focused look at `mm/kmsan/hooks.c:249`. I'm going to carefully examine the code at that line. This hook is likely where the memory safety magic is happening, or perhaps where something unexpected is triggering. I need to understand exactly what's being intercepted and how it's interacting with the KMSAN instrumentation. I expect to see function calls, variable assignments, and conditional statements that are crucial to identifying the behavior that’s leading to the observed issue. I need to consider all possible execution paths and any associated data dependencies to anticipate any potential misbehaviors or edge-case scenarios. Let’s see what's really going on in there. |
| 32/3 | 2026/09/24 01:09 | tool | read-file |
0mArgs:{
"File": "mm/kmsan/hooks.c",
"FirstLine": 245,
"LineCount": 45
}Results: {
"Contents": " 245:\t\tflush_cache_vmap(vmalloc_origin(start), vmalloc_origin(end));\n 246:\t\tkmsan_leave_runtime();\n 247:\t}\n 248:\t\n 249:\tvoid kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,\n 250:\t\t\t\tsize_t left)\n 251:\t{\n 252:\t\tunsigned long ua_flags;\n 253:\t\n 254:\t\tif (!kmsan_enabled || kmsan_in_runtime())\n 255:\t\t\treturn;\n 256:\t\t/*\n 257:\t\t * At this point we've copied the memory already. It's hard to check it\n 258:\t\t * before copying, as the size of actually copied buffer is unknown.\n 259:\t\t */\n 260:\t\n 261:\t\t/* copy_to_user() may copy zero bytes. No need to check. */\n 262:\t\tif (!to_copy)\n 263:\t\t\treturn;\n 264:\t\t/* Or maybe copy_to_user() failed to copy anything. */\n 265:\t\tif (to_copy \u003c= left)\n 266:\t\t\treturn;\n 267:\t\n 268:\t\tua_flags = user_access_save();\n 269:\t\tif (!IS_ENABLED(CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE) ||\n 270:\t\t (u64)to \u003c TASK_SIZE) {\n 271:\t\t\t/* This is a user memory access, check it. */\n 272:\t\t\tkmsan_internal_check_memory((void *)from, to_copy - left, to,\n 273:\t\t\t\t\t\t REASON_COPY_TO_USER);\n 274:\t\t} else {\n 275:\t\t\t/* Otherwise this is a kernel memory access. This happens when a\n 276:\t\t\t * compat syscall passes an argument allocated on the kernel\n 277:\t\t\t * stack to a real syscall.\n 278:\t\t\t * Don't check anything, just copy the shadow of the copied\n 279:\t\t\t * bytes.\n 280:\t\t\t */\n 281:\t\t\tkmsan_enter_runtime();\n 282:\t\t\tkmsan_internal_memmove_metadata((void *)to, (void *)from,\n 283:\t\t\t\t\t\t\tto_copy - left);\n 284:\t\t\tkmsan_leave_runtime();\n 285:\t\t}\n 286:\t\tuser_access_restore(ua_flags);\n 287:\t}\n 288:\tEXPORT_SYMBOL(kmsan_copy_to_user);\n 289:\t\n"
} |
| 33/3 | 2026/09/24 01:09 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 9190 output: 20 thoughts: 85 Thoughts: Here's my take on this – a distilled thought process as if I were working through it: **KMSAN Memory Check Analysis** Okay, so I'm looking at this `kmsan_internal_check_memory` call: `kmsan_internal_check_memory((void *)from, to_copy - left, to, REASON_COPY_TO_USER)`. Standard KMSAN memory checking, `from` to `to`, checking a chunk of memory during a copy to userspace. Nothing immediately jumping out there. But wait a minute, how does this interact with the page cache, and particularly, `page_alloc`? Does KMSAN do anything specific for pages pulled from the page cache? I need to understand if there's any special handling or potential gotchas when memory originates from a cached page, or if `page_alloc` has some specific interactions that I need to be aware of in the context of KMSAN. My immediate course of action is to dive into `mm/kmsan/core.c` – that's the central KMSAN code – or do a quick search for any mentions of "pagecache" or "alloc_pages" within the KMSAN codebase. That's the best route to find the interaction. This is key to determine if I'm missing something that should be accounted for when checking memory regions in this context. |
| 34/3 | 2026/09/24 01:09 | tool | grepper |
0mArgs:{
"Expression": "kmsan_alloc_page"
}Results: {
"Output": "include/linux/kmsan.h=57=bool __init __must_check kmsan_memblock_free_pages(struct page *page,\n--\ninclude/linux/kmsan.h-60-/**\ninclude/linux/kmsan.h:61: * kmsan_alloc_page() - Notify KMSAN about an alloc_pages() call.\ninclude/linux/kmsan.h-62- * @page: struct page pointer returned by alloc_pages().\n--\ninclude/linux/kmsan.h-68- */\ninclude/linux/kmsan.h:69:void kmsan_alloc_page(struct page *page, unsigned int order, gfp_t flags);\ninclude/linux/kmsan.h-70-\n--\ninclude/linux/kmsan.h=315=static inline void kmsan_task_exit(struct task_struct *task)\n--\ninclude/linux/kmsan.h-318-\ninclude/linux/kmsan.h:319:static inline void kmsan_alloc_page(struct page *page, unsigned int order,\ninclude/linux/kmsan.h-320-\t\t\t\t gfp_t flags)\n--\nmm/kmsan/shadow.c=169=EXPORT_SYMBOL(kmsan_copy_page_meta);\nmm/kmsan/shadow.c-170-\nmm/kmsan/shadow.c:171:void kmsan_alloc_page(struct page *page, unsigned int order, gfp_t flags)\nmm/kmsan/shadow.c-172-{\n--\nmm/page_alloc.c=5162=unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,\n--\nmm/page_alloc.c-5285-\t\ttrace_mm_page_alloc(page, 0, gfp, ac.migratetype);\nmm/page_alloc.c:5286:\t\tkmsan_alloc_page(page, 0, gfp \u0026 ~__GFP_RECLAIM);\nmm/page_alloc.c-5287-\t\tset_page_refcounted(page);\n--\nmm/page_alloc.c=5348=static inline bool alloc_nolock_allowed(void)\n--\nmm/page_alloc.c-5373- *\nmm/page_alloc.c:5374: * Specify __GFP_ZERO to make sure that call to kmsan_alloc_page() below\nmm/page_alloc.c-5375- * is safe in any context. Also zeroing the page is mandatory for\n--\nmm/page_alloc.c=5388=struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,\n--\nmm/page_alloc.c-5464-\ttrace_mm_page_alloc(page, order, alloc_gfp, ac.migratetype);\nmm/page_alloc.c:5465:\tkmsan_alloc_page(page, order, alloc_gfp);\nmm/page_alloc.c-5466-\n"
} |
| 35/3 | 2026/09/24 01:09 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 10345 output: 36 thoughts: 18 Thoughts: Okay, here's my interpretation of what's going on, formatted as you requested: **Navigating the Shadow Memory Realm** Alright, let's dive right in. The line I'm looking at, `mm/kmsan/shadow.c:171`, immediately tells me we're dealing with KernelMemorySanitizer, or KMSAN. Specifically, I'm peering into the heart of its shadow memory management. That specific line? It's likely a critical piece of the puzzle within KSMAN. Line 171 is crucial. My immediate thoughts go to what the shadow memory is being used for. It's the crux of KSMAN. My assumption is that I'll be able to work out the role the line is performing from its context. Is it allocation? Mapping shadow memory? Perhaps marking memory as tainted or clean? Or, maybe it's related to shadow memory synchronization during context switches or inter-processor communication. The `mm` directory confirms we're in memory management territory. I'm going to have to quickly grasp the code around this line to grasp its significance. I'll need to know whether its an access to the shadow itself, a means of assigning the shadow, or maybe dealing with meta-data regarding shadow. I'll need to know which to know how to proceed. |
| 36/3 | 2026/09/24 01:09 | tool | read-file |
0mArgs:{
"File": "mm/kmsan/shadow.c",
"FirstLine": 170,
"LineCount": 40
}Results: {
"Contents": " 170:\t\n 171:\tvoid kmsan_alloc_page(struct page *page, unsigned int order, gfp_t flags)\n 172:\t{\n 173:\t\tbool initialized = (flags \u0026 __GFP_ZERO) || !kmsan_enabled;\n 174:\t\tstruct page *shadow, *origin;\n 175:\t\tdepot_stack_handle_t handle;\n 176:\t\tint pages = 1 \u003c\u003c order;\n 177:\t\n 178:\t\tif (!page)\n 179:\t\t\treturn;\n 180:\t\n 181:\t\tshadow = shadow_page_for(page);\n 182:\t\torigin = origin_page_for(page);\n 183:\t\n 184:\t\tif (initialized) {\n 185:\t\t\t__memset(page_address(shadow), 0, PAGE_SIZE * pages);\n 186:\t\t\t__memset(page_address(origin), 0, PAGE_SIZE * pages);\n 187:\t\t\treturn;\n 188:\t\t}\n 189:\t\n 190:\t\t/* Zero pages allocated by the runtime should also be initialized. */\n 191:\t\tif (kmsan_in_runtime())\n 192:\t\t\treturn;\n 193:\t\n 194:\t\t__memset(page_address(shadow), -1, PAGE_SIZE * pages);\n 195:\t\tkmsan_enter_runtime();\n 196:\t\thandle = kmsan_save_stack_with_flags(flags, /*extra_bits*/ 0);\n 197:\t\tkmsan_leave_runtime();\n 198:\t\t/*\n 199:\t\t * Addresses are page-aligned, pages are contiguous, so it's ok\n 200:\t\t * to just fill the origin pages with @handle.\n 201:\t\t */\n 202:\t\tfor (int i = 0; i \u003c PAGE_SIZE * pages / sizeof(handle); i++)\n 203:\t\t\t((depot_stack_handle_t *)page_address(origin))[i] = handle;\n 204:\t}\n 205:\t\n 206:\tvoid kmsan_free_page(struct page *page, unsigned int order)\n 207:\t{\n 208:\t\tif (!kmsan_enabled || kmsan_in_runtime())\n 209:\t\t\treturn;\n"
} |
| 37/3 | 2026/09/24 01:09 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 11297 output: 29 thoughts: 37 Thoughts: Okay, here's my take on those thoughts, framed as an expert's internal monologue: **KMSAN Page Tracking: A Deep Dive** Hold on a minute. I need to clarify something crucial about KMSAN's behavior when dealing with file pages. Specifically, I'm thinking about the lifecycle of memory brought into the kernel from disk or over the network. When those pages are read in, does KMSAN immediately get involved? Does it *track* those newly acquired pages, or does it do the opposite and *unpoison* them? That distinction is important. I need to confirm KMSAN's handling of file pages. Let me track down the specific functions or locations within the kernel source code where this unpoisoning of file pages or memory happens. That's the key to understanding how KMSAN interacts with file data, and it's essential to understand its coverage characteristics in real-world kernel operations. The details matter here, and I need to solidify my understanding of these lower level behaviors. |
| 38/3 | 2026/09/24 01:09 | tool | grepper |
0mError:no matches Args: {
"Expression": "kmsan_unpoison_memory",
"PathPrefix": "fs/"
}Results: {
"error": "no matches"
} |
| 39/3 | 2026/09/24 01:09 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 11588 output: 19 thoughts: 14 Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience, presented in the first person: **Kernel-Wide KMSAN Poison Analysis** Right, let's dive into this. My immediate thought is to systematically analyze the `kmsan_unpoison` function across the entire kernel codebase. I need to get a handle on its usage patterns, the contexts in which it's employed, and the potential implications of those invocations. This is going to require a targeted code search – ideally using something robust like `cscope`, `grep`, or even something more sophisticated if available. The goal isn't just to *find* the calls, but to *understand* them. I'll need to look at call sites, arguments passed, and what happens before and after the `kmsan_unpoison` call itself. I'll be paying close attention to any instances where `kmsan_unpoison` is used with potentially problematic regions of memory, focusing on areas identified by previous vulnerability research, or areas commonly associated with memory safety issues. Areas like device drivers, networking stacks, and any code that deals directly with user-supplied data will be under extra scrutiny. Ideally, I'd like to get a solid grasp of any patterns or common usage idioms around unpoisoning operations. Understanding these could highlight potential vulnerabilities or at least provide clues as to where issues are most likely to occur. It's about finding the 'hotspots' for potential memory safety problems, and the best way to do that is a broad yet focused scan. |
| 40/3 | 2026/09/24 01:09 | tool | grepper |
0mArgs:{
"Expression": "kmsan_unpoison"
}Results: {
"Output": "arch/s390/boot/kmsan.c-3-\narch/s390/boot/kmsan.c:4:void kmsan_unpoison_memory(const void *address, size_t size)\narch/s390/boot/kmsan.c-5-{\n--\narch/s390/include/asm/cpacf.h=300=static __always_inline void __cpacf_query(unsigned int opcode,\n--\narch/s390/include/asm/cpacf.h-303-\t__cpacf_query_insn(opcode, mask, CPACF_FC_QUERY);\narch/s390/include/asm/cpacf.h:304:\tkmsan_unpoison_memory(mask, sizeof(*mask));\narch/s390/include/asm/cpacf.h-305-}\n--\narch/s390/include/asm/cpacf.h=371=static __always_inline void __cpacf_qai(unsigned int opcode, cpacf_qai_t *qai)\n--\narch/s390/include/asm/cpacf.h-373-\t__cpacf_query_insn(opcode, qai, CPACF_FC_QUERY_AUTH_INFO);\narch/s390/include/asm/cpacf.h:374:\tkmsan_unpoison_memory(qai, sizeof(*qai));\narch/s390/include/asm/cpacf.h-375-}\n--\narch/s390/include/asm/cpacf.h=409=static inline int cpacf_km(unsigned long func, void *param,\n--\narch/s390/include/asm/cpacf.h-426-\narch/s390/include/asm/cpacf.h:427:\tkmsan_unpoison_memory(dest, src_len - s.odd);\narch/s390/include/asm/cpacf.h-428-\treturn src_len - s.odd;\n--\narch/s390/include/asm/cpacf.h=442=static inline int cpacf_kmc(unsigned long func, void *param,\n--\narch/s390/include/asm/cpacf.h-459-\narch/s390/include/asm/cpacf.h:460:\tkmsan_unpoison_memory(dest, src_len - s.odd);\narch/s390/include/asm/cpacf.h-461-\treturn src_len - s.odd;\n--\narch/s390/include/asm/cpacf.h=574=static inline int cpacf_kmctr(unsigned long func, void *param, u8 *dest,\n--\narch/s390/include/asm/cpacf.h-593-\narch/s390/include/asm/cpacf.h:594:\tkmsan_unpoison_memory(dest, src_len - s.odd);\narch/s390/include/asm/cpacf.h-595-\treturn src_len - s.odd;\n--\narch/s390/include/asm/cpacf.h=608=static inline void cpacf_prno(unsigned long func, void *param,\n--\narch/s390/include/asm/cpacf.h-626-\t\t: \"cc\", \"memory\", \"0\", \"1\");\narch/s390/include/asm/cpacf.h:627:\tkmsan_unpoison_memory(dest, dest_len);\narch/s390/include/asm/cpacf.h-628-}\n--\narch/s390/include/asm/cpacf.h=637=static inline void cpacf_trng(u8 *ucbuf, unsigned long ucbuf_len,\n--\narch/s390/include/asm/cpacf.h-652-\t\t: \"cc\", \"memory\", \"0\");\narch/s390/include/asm/cpacf.h:653:\tkmsan_unpoison_memory(ucbuf, ucbuf_len);\narch/s390/include/asm/cpacf.h:654:\tkmsan_unpoison_memory(cbuf, cbuf_len);\narch/s390/include/asm/cpacf.h-655-}\n--\narch/s390/include/asm/cpu_mf.h=235=static __always_inline int stcctm(enum stcctm_ctr_set set, u64 range, u64 *dest)\n--\narch/s390/include/asm/cpu_mf.h-248-\t */\narch/s390/include/asm/cpu_mf.h:249:\tkmsan_unpoison_memory(dest, range * sizeof(u64));\narch/s390/include/asm/cpu_mf.h-250-\treturn CC_TRANSFORM(cc);\n--\narch/s390/include/asm/fpu-insn.h=388=static __always_inline void fpu_vstl(u8 v1, u32 index, const void *vxr)\n--\narch/s390/include/asm/fpu-insn.h-397-\t\t : \"memory\");\narch/s390/include/asm/fpu-insn.h:398:\tkmsan_unpoison_memory(vxr, size);\narch/s390/include/asm/fpu-insn.h-399-}\n--\narch/s390/include/asm/fpu-insn.h=403=static __always_inline void fpu_vstl(u8 v1, u32 index, const void *vxr)\n--\narch/s390/include/asm/fpu-insn.h-414-\t\t: \"memory\", \"1\");\narch/s390/include/asm/fpu-insn.h:415:\tkmsan_unpoison_memory(vxr, size);\narch/s390/include/asm/fpu-insn.h-416-}\n--\narch/s390/kernel/ftrace.c=283=void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,\n--\narch/s390/kernel/ftrace.c-297-\narch/s390/kernel/ftrace.c:298:\tkmsan_unpoison_memory(fregs, ftrace_regs_size());\narch/s390/kernel/ftrace.c-299-\tregs = ftrace_get_regs(fregs);\n--\narch/s390/kernel/traps.c=293=void kernel_stack_invalid(struct pt_regs *regs)\n--\narch/s390/kernel/traps.c-298-\t */\narch/s390/kernel/traps.c:299:\tkmsan_unpoison_entry_regs(regs);\narch/s390/kernel/traps.c-300-\tbust_spinlocks(1);\n--\narch/x86/include/asm/page_64.h=85=static inline void clear_pages(void *addr, unsigned int npages)\n--\narch/x86/include/asm/page_64.h-91-\t */\narch/x86/include/asm/page_64.h:92:\tkmsan_unpoison_memory(addr, len);\narch/x86/include/asm/page_64.h-93-\n--\narch/x86/kernel/traps.c=401=noinstr bool handle_bug(struct pt_regs *regs)\n--\narch/x86/kernel/traps.c-420-\t */\narch/x86/kernel/traps.c:421:\tkmsan_unpoison_entry_regs(regs);\narch/x86/kernel/traps.c-422-\t/*\n--\narch/x86/lib/iomem.c=26=static void string_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)\n--\narch/x86/lib/iomem.c-44-\t/* KMSAN must treat values read from devices as initialized. */\narch/x86/lib/iomem.c:45:\tkmsan_unpoison_memory(orig_to, orig_n);\narch/x86/lib/iomem.c-46-}\n--\ncrypto/jitterentropy-kcapi.c=102=void jent_hash_time(struct sha3_ctx *hash_state, __u64 time, u8 *addtl,\n--\ncrypto/jitterentropy-kcapi.c-109-\ncrypto/jitterentropy-kcapi.c:110:\tkmsan_unpoison_memory(intermediary, sizeof(intermediary));\ncrypto/jitterentropy-kcapi.c-111-\n--\ndrivers/input/serio/libps2.c=262=int __ps2_command(struct ps2dev *ps2dev, u8 *param, unsigned int command)\n--\ndrivers/input/serio/libps2.c-354-\t\t\tparam[i] = ps2dev-\u003ecmdbuf[(receive - 1) - i];\ndrivers/input/serio/libps2.c:355:\t\tkmsan_unpoison_memory(param, receive);\ndrivers/input/serio/libps2.c-356-\t}\n--\ninclude/linux/highmem.h=396=static inline void copy_user_highpage(struct page *to, struct page *from,\n--\ninclude/linux/highmem.h-403-\tcopy_user_page(vto, vfrom, vaddr, to);\ninclude/linux/highmem.h:404:\tkmsan_unpoison_memory(page_address(to), PAGE_SIZE);\ninclude/linux/highmem.h-405-\tkunmap_local(vto);\n--\ninclude/linux/highmem.h=434=static inline int copy_mc_user_highpage(struct page *to, struct page *from,\n--\ninclude/linux/highmem.h-443-\tif (!ret)\ninclude/linux/highmem.h:444:\t\tkmsan_unpoison_memory(page_address(to), PAGE_SIZE);\ninclude/linux/highmem.h-445-\tkunmap_local(vto);\n--\ninclude/linux/instrumented.h=161=instrument_copy_from_user_after(const void *to, const void __user *from,\n--\ninclude/linux/instrumented.h-163-{\ninclude/linux/instrumented.h:164:\tkmsan_unpoison_memory(to, n - left);\ninclude/linux/instrumented.h-165-}\n--\ninclude/linux/instrumented.h=195=static __always_inline void instrument_memcpy_after(void *to, const void *from,\n--\ninclude/linux/instrumented.h-212-\tu64 __tmp = (u64)(to);\t\t\t\t\\\ninclude/linux/instrumented.h:213:\tkmsan_unpoison_memory(\u0026__tmp, sizeof(__tmp));\t\\\ninclude/linux/instrumented.h-214-\tto = __tmp;\t\t\t\t\t\\\n--\ninclude/linux/irq-entry-common.h=98=static __always_inline void enter_from_user_mode(struct pt_regs *regs)\n--\ninclude/linux/irq-entry-common.h-106-\tinstrumentation_begin();\ninclude/linux/irq-entry-common.h:107:\tkmsan_unpoison_entry_regs(regs);\ninclude/linux/irq-entry-common.h-108-\ttrace_hardirqs_off_finish();\n--\ninclude/linux/irq-entry-common.h=382=static __always_inline irqentry_state_t irqentry_enter_from_kernel_mode(struct pt_regs *regs)\n--\ninclude/linux/irq-entry-common.h-420-\t\tinstrumentation_begin();\ninclude/linux/irq-entry-common.h:421:\t\tkmsan_unpoison_entry_regs(regs);\ninclude/linux/irq-entry-common.h-422-\t\ttrace_hardirqs_off_finish();\n--\ninclude/linux/irq-entry-common.h-436-\tinstrumentation_begin();\ninclude/linux/irq-entry-common.h:437:\tkmsan_unpoison_entry_regs(regs);\ninclude/linux/irq-entry-common.h-438-\trcu_irq_enter_check_tick();\n--\ninclude/linux/kmsan-checks.h=27=void kmsan_poison_memory(const void *address, size_t size, gfp_t flags);\n--\ninclude/linux/kmsan-checks.h-29-/**\ninclude/linux/kmsan-checks.h:30: * kmsan_unpoison_memory() - Mark the memory range as initialized.\ninclude/linux/kmsan-checks.h-31- * @address: address to start with.\n--\ninclude/linux/kmsan-checks.h-36- */\ninclude/linux/kmsan-checks.h:37:void kmsan_unpoison_memory(const void *address, size_t size);\ninclude/linux/kmsan-checks.h-38-\n--\ninclude/linux/kmsan-checks.h=77=static inline void kmsan_poison_memory(const void *address, size_t size,\n--\ninclude/linux/kmsan-checks.h-80-}\ninclude/linux/kmsan-checks.h:81:static inline void kmsan_unpoison_memory(const void *address, size_t size)\ninclude/linux/kmsan-checks.h-82-{\n--\ninclude/linux/kmsan.h=221=void kmsan_handle_urb(const struct urb *urb, bool is_out);\n--\ninclude/linux/kmsan.h-223-/**\ninclude/linux/kmsan.h:224: * kmsan_unpoison_entry_regs() - Handle pt_regs in low-level entry code.\ninclude/linux/kmsan.h-225- * @regs:\tstruct pt_regs pointer received from assembly code.\n--\ninclude/linux/kmsan.h-227- * KMSAN unpoisons the contents of the passed pt_regs, preventing potential\ninclude/linux/kmsan.h:228: * false positive reports. Unlike kmsan_unpoison_memory(),\ninclude/linux/kmsan.h:229: * kmsan_unpoison_entry_regs() can be called from the regions where\ninclude/linux/kmsan.h-230- * kmsan_in_runtime() returns true, which is the case in early entry code.\ninclude/linux/kmsan.h-231- */\ninclude/linux/kmsan.h:232:void kmsan_unpoison_entry_regs(const struct pt_regs *regs);\ninclude/linux/kmsan.h-233-\n--\ninclude/linux/kmsan.h=386=static inline void kmsan_handle_urb(const struct urb *urb, bool is_out)\n--\ninclude/linux/kmsan.h-389-\ninclude/linux/kmsan.h:390:static inline void kmsan_unpoison_entry_regs(const struct pt_regs *regs)\ninclude/linux/kmsan.h-391-{\n--\nkernel/bpf/core.c=2412=static unsigned int PROG_NAME(stack_size)(const void *ctx, const struct bpf_insn *insn) \\\n--\nkernel/bpf/core.c-2416-\\\nkernel/bpf/core.c:2417:\tkmsan_unpoison_memory(stack, sizeof(stack)); \\\nkernel/bpf/core.c-2418-\tFP = (u64) (unsigned long) \u0026stack[ARRAY_SIZE(stack)]; \\\n--\nkernel/bpf/core.c=2425=static u64 PROG_NAME_ARGS(stack_size)(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5, \\\n--\nkernel/bpf/core.c-2430-\\\nkernel/bpf/core.c:2431:\tkmsan_unpoison_memory(stack, sizeof(stack)); \\\nkernel/bpf/core.c-2432-\tFP = (u64) (unsigned long) \u0026stack[ARRAY_SIZE(stack)]; \\\n--\nkernel/dma/swiotlb.c=1016=static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size,\n--\nkernel/dma/swiotlb.c-1075-\t\t\t} else {\nkernel/dma/swiotlb.c:1076:\t\t\t\tkmsan_unpoison_memory(vaddr, sz);\nkernel/dma/swiotlb.c-1077-\t\t\t\tmemcpy_to_page(page, offset, vaddr, sz);\n--\nkernel/dma/swiotlb.c-1094-\t} else {\nkernel/dma/swiotlb.c:1095:\t\tkmsan_unpoison_memory(vaddr, size);\nkernel/dma/swiotlb.c-1096-\t\tmemcpy(phys_to_virt(orig_addr), vaddr, size);\n--\nkernel/entry/common.c=170=irqentry_state_t noinstr irqentry_nmi_enter(struct pt_regs *regs)\n--\nkernel/entry/common.c-181-\tinstrumentation_begin();\nkernel/entry/common.c:182:\tkmsan_unpoison_entry_regs(regs);\nkernel/entry/common.c-183-\ttrace_hardirqs_off_finish();\n--\nkernel/kcov.c=147=static void kcov_remote_area_put(struct kcov_remote_area *area,\n--\nkernel/kcov.c-157-\t */\nkernel/kcov.c:158:\tkmsan_unpoison_memory(\u0026area-\u003elist, sizeof(area-\u003elist));\nkernel/kcov.c-159-}\n--\nkernel/trace/ftrace.c=8607=void arch_ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,\n--\nkernel/trace/ftrace.c-8609-{\nkernel/trace/ftrace.c:8610:\tkmsan_unpoison_memory(fregs, ftrace_regs_size());\nkernel/trace/ftrace.c-8611-\t__ftrace_ops_list_func(ip, parent_ip, NULL, fregs);\n--\nlib/crypto/arm64/sha256.h=44=static bool sha256_finup_2x_arch(const struct __sha256_ctx *ctx,\n--\nlib/crypto/arm64/sha256.h-53-\t\t\tsha256_ce_finup2x(ctx, data1, data2, len, out1, out2);\nlib/crypto/arm64/sha256.h:54:\t\tkmsan_unpoison_memory(out1, SHA256_DIGEST_SIZE);\nlib/crypto/arm64/sha256.h:55:\t\tkmsan_unpoison_memory(out2, SHA256_DIGEST_SIZE);\nlib/crypto/arm64/sha256.h-56-\t\treturn true;\n--\nlib/crypto/s390/sha3.h=64=static inline bool s390_sha3(int func, const u8 *in, size_t in_len,\n--\nlib/crypto/s390/sha3.h-79-\tif (static_branch_likely(\u0026have_sha3_init_optim))\nlib/crypto/s390/sha3.h:80:\t\tkmsan_unpoison_memory(\u0026state, out_len);\nlib/crypto/s390/sha3.h-81-\n--\nlib/crypto/x86/sha256.h=70=static bool sha256_finup_2x_arch(const struct __sha256_ctx *ctx,\n--\nlib/crypto/x86/sha256.h-84-\t\tkernel_fpu_end();\nlib/crypto/x86/sha256.h:85:\t\tkmsan_unpoison_memory(out1, SHA256_DIGEST_SIZE);\nlib/crypto/x86/sha256.h:86:\t\tkmsan_unpoison_memory(out2, SHA256_DIGEST_SIZE);\nlib/crypto/x86/sha256.h-87-\t\treturn true;\n--\nlib/iomap.c=360=void ioread8_rep(const void __iomem *addr, void *dst, unsigned long count)\n--\nlib/iomap.c-363-\t/* KMSAN must treat values read from devices as initialized. */\nlib/iomap.c:364:\tkmsan_unpoison_memory(dst, count);\nlib/iomap.c-365-}\nlib/iomap.c=366=void ioread16_rep(const void __iomem *addr, void *dst, unsigned long count)\n--\nlib/iomap.c-369-\t/* KMSAN must treat values read from devices as initialized. */\nlib/iomap.c:370:\tkmsan_unpoison_memory(dst, count * 2);\nlib/iomap.c-371-}\nlib/iomap.c=372=void ioread32_rep(const void __iomem *addr, void *dst, unsigned long count)\n--\nlib/iomap.c-375-\t/* KMSAN must treat values read from devices as initialized. */\nlib/iomap.c:376:\tkmsan_unpoison_memory(dst, count * 4);\nlib/iomap.c-377-}\n--\nlib/stackdepot.c=434=depot_alloc_stack(unsigned long *entries, unsigned int nr_entries, u32 hash, depot_flags_t flags, void **prealloc)\n--\nlib/stackdepot.c-487-\t */\nlib/stackdepot.c:488:\tkmsan_unpoison_memory(stack, record_size);\nlib/stackdepot.c-489-\n--\nlib/stackdepot.c=760=unsigned int stack_depot_fetch(depot_stack_handle_t handle,\n--\nlib/stackdepot.c-769-\t */\nlib/stackdepot.c:770:\tkmsan_unpoison_memory(entries, sizeof(*entries));\nlib/stackdepot.c-771-\n--\nlib/zlib_dfltcc/dfltcc_util.h=29=static inline dfltcc_cc dfltcc(\n--\nlib/zlib_dfltcc/dfltcc_util.h-71- case DFLTCC_QAF:\nlib/zlib_dfltcc/dfltcc_util.h:72: kmsan_unpoison_memory(param, sizeof(struct dfltcc_qaf_param));\nlib/zlib_dfltcc/dfltcc_util.h-73- break;\nlib/zlib_dfltcc/dfltcc_util.h-74- case DFLTCC_GDHT:\nlib/zlib_dfltcc/dfltcc_util.h:75: kmsan_unpoison_memory(param, offsetof(struct dfltcc_param_v0, csb));\nlib/zlib_dfltcc/dfltcc_util.h-76- break;\nlib/zlib_dfltcc/dfltcc_util.h-77- case DFLTCC_CMPR:\nlib/zlib_dfltcc/dfltcc_util.h:78: kmsan_unpoison_memory(param, sizeof(struct dfltcc_param_v0));\nlib/zlib_dfltcc/dfltcc_util.h:79: kmsan_unpoison_memory(\nlib/zlib_dfltcc/dfltcc_util.h-80- orig_t2,\n--\nlib/zlib_dfltcc/dfltcc_util.h-84- case DFLTCC_XPND:\nlib/zlib_dfltcc/dfltcc_util.h:85: kmsan_unpoison_memory(param, sizeof(struct dfltcc_param_v0));\nlib/zlib_dfltcc/dfltcc_util.h:86: kmsan_unpoison_memory(orig_t2, t2 - orig_t2);\nlib/zlib_dfltcc/dfltcc_util.h-87- break;\n--\nmm/kmsan/hooks.c=393=EXPORT_SYMBOL(kmsan_poison_memory);\n--\nmm/kmsan/hooks.c-398- */\nmm/kmsan/hooks.c:399:void kmsan_unpoison_memory(const void *address, size_t size)\nmm/kmsan/hooks.c-400-{\n--\nmm/kmsan/hooks.c-411-}\nmm/kmsan/hooks.c:412:EXPORT_SYMBOL(kmsan_unpoison_memory);\nmm/kmsan/hooks.c-413-\nmm/kmsan/hooks.c-414-/*\nmm/kmsan/hooks.c:415: * Version of kmsan_unpoison_memory() called from IRQ entry functions.\nmm/kmsan/hooks.c-416- */\nmm/kmsan/hooks.c:417:void kmsan_unpoison_entry_regs(const struct pt_regs *regs)\nmm/kmsan/hooks.c-418-{\nmm/kmsan/hooks.c:419:\tkmsan_unpoison_memory((void *)regs, sizeof(*regs));\nmm/kmsan/hooks.c-420-}\n--\nmm/kmsan/kmsan_test.c=670=static void test_stackdepot_roundtrip(struct kunit *test)\n--\nmm/kmsan/kmsan_test.c-691-/*\nmm/kmsan/kmsan_test.c:692: * Test case: ensure that kmsan_unpoison_memory() and the instrumentation work\nmm/kmsan/kmsan_test.c-693- * the same.\n--\nmm/kmsan/kmsan_test.c=695=static void test_unpoison_memory(struct kunit *test)\n--\nmm/kmsan/kmsan_test.c-701-\t\ttest,\nmm/kmsan/kmsan_test.c:702:\t\t\"unpoisoning via the instrumentation vs. kmsan_unpoison_memory() (2 UMR reports)\\n\");\nmm/kmsan/kmsan_test.c-703-\n--\nmm/kmsan/kmsan_test.c-711-\t/* Initialize b[0] and check b[1]--b[3]. */\nmm/kmsan/kmsan_test.c:712:\tkmsan_unpoison_memory((char *)\u0026b[0], 1);\nmm/kmsan/kmsan_test.c-713-\tkmsan_check_memory((char *)\u0026b[1], 3);\n--\nmm/slub.c=9705=static char *create_unique_id(struct kmem_cache *s)\n--\nmm/slub.c-9738-\t}\nmm/slub.c:9739:\tkmsan_unpoison_memory(name, p - name);\nmm/slub.c-9740-\treturn name;\n--\nmm/slub.c=9815=int sysfs_slab_alias(struct kmem_cache *s, const char *name)\n--\nmm/slub.c-9839-\talias_list = al;\nmm/slub.c:9840:\tkmsan_unpoison_memory(al, sizeof(*al));\nmm/slub.c-9841-\treturn 0;\n--\ntools/objtool/check.c=1095=static const char *uaccess_safe_builtin[] = {\n--\ntools/objtool/check.c-1237-\t\"kmsan_report\",\ntools/objtool/check.c:1238:\t\"kmsan_unpoison_entry_regs\",\ntools/objtool/check.c:1239:\t\"kmsan_unpoison_memory\",\ntools/objtool/check.c-1240-\t\"__msan_chain_origin\",\n"
} |
| 41/3 | 2026/09/24 01:09 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 19260 output: 21 thoughts: 779 Thoughts: **Understanding the Linux Kernel's Stale Data Protection** Okay, so I'm looking at this `instrumented.h` file, specifically the `instrument_copy_from_user_after` function. What jumps out at me is that when user data is copied using `copy_from_user` or through `mmap`, the kernel unpoisons the memory in the page cache. Interesting. I recall a commit addressing this behavior and now I'm connecting the dots. The core issue, as I understand it, is about protecting against stale data exposure when files are extended, especially after having been accessed via `mmap`. Let me break it down: A process creates a small file, say 10 bytes. The kernel, being the kernel, allocates a 4KB page cache folio to back it. Then, the process `mmaps` this file, potentially mapping the entire 4KB folio into its address space. Now, the process writes some data, maybe from offset 100 to 200 within that 4KB folio *using the mmap pointer*. No problem – the write succeeds. The problem arises when another process, or the same one, later extends the file, say to 500 bytes. This extension, perhaps through `lseek` and `write` or `ftruncate`, should, according to POSIX, ensure that the *gap* between the original EOF (10 bytes) and the new EOF (500 bytes) contains *zeroes*. That's the expected behavior. However, the `mmap` write dirtied the folio past the original EOF. This means that if the kernel doesn't explicitly zero out the stale data between the old and new EOF in that folio, reads from the extended file would potentially expose the data written via mmap, and not the zeroes that the standard specifies. Now, hold on... is this truly *uninitialized* memory, or is it better to think of it as *stale user data*? It's the latter; it's user data, because the user explicitly wrote to that memory via `mmap`. But then again... even if there was no `mmap` at all, and a page was allocated without `GFP_ZERO` flag (or, with the flag but still), `pagecache_isize_extended` or similar functions would have been called to zero-initialize the pagecache. This makes it an interesting combination of uninitialized *and* stale user data. I'm starting to remember that `cifs_setsize` used to use `pagecache_isize_extended` before this patch. Looking at the comment in the code, I see why this was changed. It's about zeroing out the tail of the folio when extending the file. This mirrors the behavior of `pagecache_isize_extended`, but the latter is a no-op when block size is >= `PAGE_SIZE`, as is the case for CIFS. `truncate_pagecache` then drops the pagecache beyond the new EOF, like in `truncate_setsize`. So, the key here is the distinction between what we *expect* versus what actually happens. The kernel *must* clear stale data beyond the original EOF when the file is extended to prevent this data from being revealed and not initialized to zero. |
| 42/3 | 2026/09/24 01:09 | tool | grepper |
0mArgs:{
"Expression": "pagecache_isize_extended"
}Results: {
"Output": "fs/afs/inode.c=713=static void afs_setattr_success(struct afs_operation *op)\n--\nfs/afs/inode.c-725-\t\tif (size \u003e old_i_size)\nfs/afs/inode.c:726:\t\t\tpagecache_isize_extended(inode, old_i_size, size);\nfs/afs/inode.c-727-\t}\n--\nfs/btrfs/file.c=1318=ssize_t btrfs_buffered_write(struct kiocb *iocb, struct iov_iter *iter)\n--\nfs/btrfs/file.c-1339-\t * other buffered writes and cause incorrect call of\nfs/btrfs/file.c:1340:\t * pagecache_isize_extended() to overwrite existing data.\nfs/btrfs/file.c-1341-\t */\n--\nfs/btrfs/file.c-1363-\tif (num_written \u003e 0) {\nfs/btrfs/file.c:1364:\t\tpagecache_isize_extended(inode, old_isize, iocb-\u003eki_pos);\nfs/btrfs/file.c-1365-\t\tiocb-\u003eki_pos += num_written;\n--\nfs/btrfs/inode.c=5407=static int btrfs_setsize(struct inode *inode, struct iattr *attr)\n--\nfs/btrfs/inode.c-5452-\t\tbtrfs_inode_safe_disk_i_size_write(BTRFS_I(inode), 0);\nfs/btrfs/inode.c:5453:\t\tpagecache_isize_extended(inode, oldsize, newsize);\nfs/btrfs/inode.c-5454-\t\tret = btrfs_update_inode(trans, BTRFS_I(inode));\n--\nfs/buffer.c=2180=int generic_write_end(const struct kiocb *iocb, struct address_space *mapping,\n--\nfs/buffer.c-2205-\tif (old_size \u003c pos)\nfs/buffer.c:2206:\t\tpagecache_isize_extended(inode, old_size, pos);\nfs/buffer.c-2207-\t/*\n--\nfs/exfat/file.c=25=static int exfat_cont_expand(struct inode *inode, loff_t size)\n--\nfs/exfat/file.c-87-\t * When extending file size, call truncate_pagecache() first,\nfs/exfat/file.c:88:\t * then update i_size, and call pagecache_isize_extended()\nfs/exfat/file.c-89-\t * to ensures the straddling folio is properly marked RO so\n--\nfs/exfat/file.c-91-\t */\nfs/exfat/file.c:92:\tpagecache_isize_extended(inode, oldsize, inode-\u003ei_size);\nfs/exfat/file.c-93-\n--\nfs/ext4/extents.c=4598=static int ext4_alloc_file_blocks(struct file *file, loff_t offset, loff_t len,\n--\nfs/ext4/extents.c-4767-\tif (epos \u003e old_size)\nfs/ext4/extents.c:4768:\t\tpagecache_isize_extended(inode, old_size, epos);\nfs/ext4/extents.c-4769-out:\n--\nfs/ext4/inode.c=1432=static int ext4_write_end(const struct kiocb *iocb,\n--\nfs/ext4/inode.c-1463-\tif (old_size \u003c pos \u0026\u0026 !verity)\nfs/ext4/inode.c:1464:\t\tpagecache_isize_extended(inode, old_size, pos);\nfs/ext4/inode.c-1465-\n--\nfs/ext4/inode.c=1535=static int ext4_journalled_write_end(const struct kiocb *iocb,\n--\nfs/ext4/inode.c-1580-\tif (old_size \u003c pos \u0026\u0026 !verity)\nfs/ext4/inode.c:1581:\t\tpagecache_isize_extended(inode, old_size, pos);\nfs/ext4/inode.c-1582-\n--\nfs/ext4/inode.c=3213=static int ext4_da_do_write_end(struct address_space *mapping,\n--\nfs/ext4/inode.c-3264-\tif (pos \u003e old_size)\nfs/ext4/inode.c:3265:\t\tpagecache_isize_extended(inode, old_size, pos);\nfs/ext4/inode.c-3266-\n--\nfs/ext4/inode.c=6009=int ext4_setattr(struct mnt_idmap *idmap, struct dentry *dentry,\n--\nfs/ext4/inode.c-6202-\t\t\tif (!shrink) {\nfs/ext4/inode.c:6203:\t\t\t\tpagecache_isize_extended(inode, oldsize,\nfs/ext4/inode.c-6204-\t\t\t\t\t\t\t inode-\u003ei_size);\n--\nfs/iomap/buffered-io.c=1188=static int iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i,\n--\nfs/iomap/buffered-io.c-1265-\t\tif (old_size \u003c pos \u0026\u0026 !(iter-\u003eiomap.flags \u0026 IOMAP_F_FSVERITY))\nfs/iomap/buffered-io.c:1266:\t\t\tpagecache_isize_extended(iter-\u003einode, old_size, pos);\nfs/iomap/buffered-io.c-1267-\n--\nfs/ntfs/file.c=255=static int ntfs_setattr_size(struct inode *vi, struct iattr *attr)\n--\nfs/ntfs/file.c-283-\t\ti_size_write(vi, attr-\u003eia_size);\nfs/ntfs/file.c:284:\t\tpagecache_isize_extended(vi, old_size, attr-\u003eia_size);\nfs/ntfs/file.c-285-\t} else {\n--\nfs/ntfs/file.c=1128=static long ntfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)\n--\nfs/ntfs/file.c-1199-\t\ttruncate_pagecache(vi, old_size);\nfs/ntfs/file.c:1200:\t\tpagecache_isize_extended(vi, old_size, offset);\nfs/ntfs/file.c-1201-\t}\n--\nfs/orangefs/inode.c=697=static int orangefs_setattr_size(struct inode *inode, struct iattr *iattr)\n--\nfs/orangefs/inode.c-726-\tif (iattr-\u003eia_size \u003e orig_size)\nfs/orangefs/inode.c:727:\t\tpagecache_isize_extended(inode, orig_size, iattr-\u003eia_size);\nfs/orangefs/inode.c-728-\n--\nfs/smb/client/inode.c=3056=void cifs_setsize(struct inode *inode, loff_t offset)\n--\nfs/smb/client/inode.c-3076-\t * so that data dirtied past EOF through an mmap isn't exposed once the\nfs/smb/client/inode.c:3077:\t * file is extended. This mirrors pagecache_isize_extended(), which\nfs/smb/client/inode.c-3078-\t * can't be used here as it is a no-op when the block size is \u003e=\n--\ninclude/linux/mm.h=3454=extern void truncate_setsize(struct inode *inode, loff_t newsize);\ninclude/linux/mm.h:3455:void pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to);\ninclude/linux/mm.h-3456-void truncate_pagecache_range(struct inode *inode, loff_t offset, loff_t end);\n--\nmm/truncate.c=816=void truncate_setsize(struct inode *inode, loff_t newsize)\n--\nmm/truncate.c-821-\tif (newsize \u003e oldsize)\nmm/truncate.c:822:\t\tpagecache_isize_extended(inode, oldsize, newsize);\nmm/truncate.c-823-\ttruncate_pagecache(inode, newsize);\n--\nmm/truncate.c=825=EXPORT_SYMBOL(truncate_setsize);\n--\nmm/truncate.c-827-/**\nmm/truncate.c:828: * pagecache_isize_extended - update pagecache after extension of i_size\nmm/truncate.c-829- * @inode:\tinode for which i_size was extended\n--\nmm/truncate.c-845- */\nmm/truncate.c:846:void pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to)\nmm/truncate.c-847-{\n--\nmm/truncate.c-888-}\nmm/truncate.c:889:EXPORT_SYMBOL(pagecache_isize_extended);\nmm/truncate.c-890-\n"
} |
| 43/3 | 2026/09/24 01:09 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 23194 output: 33 thoughts: 16 Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience: **Analyzing `mm/truncate.c:846`** Alright, let's dive into `mm/truncate.c:846`. Immediately, my brain starts churning – what exactly am I expecting to find at that line? Given that we're in `mm/truncate.c`, I'm primed to look at memory management aspects related to file truncation. I'm thinking about the implications on i-nodes, data blocks, page cache invalidation, potentially reallocating resources, and definitely, race conditions. This is where the core of any file size adjustment magic happens. Is it handling direct I/O? What locking mechanisms are in place? Are we dealing with page faults? Are we calling any of the fs functions? If so, which ones? My mental checklist is running through all the potential issues: security implications, error handling, performance bottlenecks... it all hinges on that single line and the surrounding context. It's time to dig in and see what the code has to say. |
| 44/3 | 2026/09/24 01:09 | tool | read-file |
0mArgs:{
"File": "mm/truncate.c",
"FirstLine": 840,
"LineCount": 55
}Results: {
"Contents": " 840:\t * The function must be called after i_size is updated so that page fault\n 841:\t * coming after we unlock the folio will already see the new i_size.\n 842:\t * The function must be called while we still hold i_rwsem - this not only\n 843:\t * makes sure i_size is stable but also that userspace cannot observe new\n 844:\t * i_size value before we are prepared to store mmap writes at new inode size.\n 845:\t */\n 846:\tvoid pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to)\n 847:\t{\n 848:\t\tint bsize = i_blocksize(inode);\n 849:\t\tloff_t rounded_from;\n 850:\t\tstruct folio *folio;\n 851:\t\n 852:\t\tWARN_ON(to \u003e inode-\u003ei_size);\n 853:\t\n 854:\t\tif (from \u003e= to || bsize \u003e= PAGE_SIZE)\n 855:\t\t\treturn;\n 856:\t\t/* Page straddling @from will not have any hole block created? */\n 857:\t\trounded_from = round_up(from, bsize);\n 858:\t\tif (to \u003c= rounded_from || !(rounded_from \u0026 (PAGE_SIZE - 1)))\n 859:\t\t\treturn;\n 860:\t\n 861:\t\tfolio = filemap_lock_folio(inode-\u003ei_mapping, from / PAGE_SIZE);\n 862:\t\t/* Folio not cached? Nothing to do */\n 863:\t\tif (IS_ERR(folio))\n 864:\t\t\treturn;\n 865:\t\t/*\n 866:\t\t * See folio_clear_dirty_for_io() for details why folio_mark_dirty()\n 867:\t\t * is needed.\n 868:\t\t */\n 869:\t\tif (folio_mkclean(folio))\n 870:\t\t\tfolio_mark_dirty(folio);\n 871:\t\n 872:\t\t/*\n 873:\t\t * The post-eof range of the folio must be zeroed before it is exposed\n 874:\t\t * to the file. Writeback normally does this, but since i_size has been\n 875:\t\t * increased we handle it here.\n 876:\t\t */\n 877:\t\tif (folio_test_dirty(folio)) {\n 878:\t\t\tunsigned int offset, end;\n 879:\t\n 880:\t\t\toffset = from - folio_pos(folio);\n 881:\t\t\tend = min_t(unsigned int, to - folio_pos(folio),\n 882:\t\t\t\t folio_size(folio));\n 883:\t\t\tfolio_zero_segment(folio, offset, end);\n 884:\t\t}\n 885:\t\n 886:\t\tfolio_unlock(folio);\n 887:\t\tfolio_put(folio);\n 888:\t}\n 889:\tEXPORT_SYMBOL(pagecache_isize_extended);\n 890:\t\n 891:\t/**\n 892:\t * truncate_pagecache_range - unmap and remove pagecache that is hole-punched\n 893:\t * @inode: inode\n 894:\t * @lstart: offset of beginning of hole\n"
} |
| 45/3 | 2026/09/24 01:09 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 24337 output: 278 thoughts: 1954 Thoughts: **KMSAN Assessment: Netfs Post-EOF Zeroing** Okay, let's break this down. My goal is to determine if this patch necessitates a KMSAN (Kernel Memory Sanitizer) check. The core change seems to be replacing calls to `pagecache_isize_extended` and similar functions with `netfs_clear_stale_post_eof` within the netfs and smb filesystems. The objective is to ensure that data written *past* the end-of-file (EOF) is zeroed out, aligning with POSIX semantics. This addresses potential issues where user-space might write to a file via `mmap` and then expect those writes to zero if the file is later extended *into* the data. First, I examine `pagecache_isize_extended` and `netfs_clear_stale_post_eof`. `pagecache_isize_extended` zeroes a segment of a folio (a page-cache-related struct), but only if the offset falls beyond the current EOF. `netfs_clear_stale_post_eof` appears to do something very similar, but more generic, fetching the folio, and zeroing out the desired segment, after clearing any stale data. The patch applies this `netfs_clear_stale_post_eof` in a few places: in buffered and direct write paths for netfs, and within `cifsfs.c` (SMB/CIFS) in `cifs_remap_file_range`, `cifs_file_copychunk_range`, and `cifs_setsize`, plus `smb3_zero_range`. The changes seem aimed at a cleaner, more generalized approach to this post-EOF zeroing. Now, the important part: are there any risks here that ONLY KMSAN can catch? 1. **Kernel structures sent to userspace:** Nope. There are no changes to structures or information passed to userspace that might be uninitialized. The focus is on *zeroing* existing data that is being modified (e.g. via an mmap write). 2. **Uninitialized variable use:** After a deep look, I can see that all variables used in `netfs_clear_stale_post_eof` and its calling functions appear properly initialized. They are either initialized on the stack or derived safely from inode fields like `i_size` which are well-managed. 3. **Allocation and Initialization:** I see no new allocations or the introduction of complex data structures where uninitialized fields could be read later. The existing structures are being *modified*, and the patch's purpose is to *zero* memory, so the risk of uninitialized use is minimal. 4. **Bounds/Length Checks:** The use of `min()` (like `min(fstart, i_size)`) is designed to handle potential inconsistencies (e.g., when the i_size might be temporarily out-of-date) in a controlled way, preventing out-of-bounds reads. I confirmed the i_size values are being read from a locked inode or otherwise well initialized. Further, `folio_zero_segment()` will protect memory. 5. **KMSAN vs. KASAN and other tools:** Potential out-of-bounds accesses *are* a risk, but KASAN (Kernel Address Sanitizer) will catch those. Locking issues are possible, but LOCKDEP would handle that. KMSAN is primarily looking for *uninitialized memory reads*. The goal here is explicitly to *initialize* the memory in the post-EOF region to zero. 6. I double-checked: the `i_size` values are read from the inode, and well initialized. I also check, in `cifsfs.c`, where we use `i_size`, that the read is well-behaved. Given all this, the patch *does not* introduce any risk of uninitialized memory usage that KMSAN uniquely detects. The primary risks, if any, are covered by KASAN, LOCKDEP, or standard coding practices. **Therefore, `NeedsKMSAN=false`. The reasoning is that the changes zero memory, are well-behaved with regards to length/size and have minimal allocation/initialization aspects.** |
| 46/3 | 2026/09/24 01:09 | tool | set-results |
0mArgs:{
"KMSANReasoning": "The patch introduces `netfs_clear_stale_post_eof()` to zero out stale pagecache data in the post-EOF region when a file is extended, preventing dirty data written via mmap beyond the previous EOF from being exposed as file content. It also adjusts truncation and invalidation ranges in CIFS.\n\n- No uninitialized stack or heap allocations/structures are introduced or modified. All local variables (`mapping`, `fgp`, `folio`, `offset`, `end`) are fully initialized scalars.\n- No uninitialized kernel memory or struct padding is copied to user space. The data cleared in the pagecache is previously written user data (or page content) to satisfy POSIX hole-zeroing semantics, not uninitialized kernel memory.\n- Any potential bugs introduced by these changes (e.g., potential out-of-bounds indexing in `folio_zero_segment()`, locking/sleeping issues under `FGP_LOCK` or `IOCB_NOWAIT`, or NULL/ERR pointer dereferences on `folio`) are covered by standard sanitizers like KASAN and LOCKDEP.\n- There are no uninitialized memory risks that would require or benefit from a dedicated KMSAN fuzzing session.",
"NeedsKMSAN": false
}Results: {
"KMSANReasoning": "The patch introduces `netfs_clear_stale_post_eof()` to zero out stale pagecache data in the post-EOF region when a file is extended, preventing dirty data written via mmap beyond the previous EOF from being exposed as file content. It also adjusts truncation and invalidation ranges in CIFS.\n\n- No uninitialized stack or heap allocations/structures are introduced or modified. All local variables (`mapping`, `fgp`, `folio`, `offset`, `end`) are fully initialized scalars.\n- No uninitialized kernel memory or struct padding is copied to user space. The data cleared in the pagecache is previously written user data (or page content) to satisfy POSIX hole-zeroing semantics, not uninitialized kernel memory.\n- Any potential bugs introduced by these changes (e.g., potential out-of-bounds indexing in `folio_zero_segment()`, locking/sleeping issues under `FGP_LOCK` or `IOCB_NOWAIT`, or NULL/ERR pointer dereferences on `folio`) are covered by standard sanitizers like KASAN and LOCKDEP.\n- There are no uninitialized memory risks that would require or benefit from a dedicated KMSAN fuzzing session.",
"NeedsKMSAN": false
} |
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