| Seq | Timestamp | Type | Name | Duration |
|---|---|---|---|---|
| 0/0 | 2026/09/11 08:55 | flow | patch-triage |
1mArgs:null Results: {
"EnableConfigs": [
"BPF_SYSCALL"
],
"FocusSymbols": [
"bpf_check",
"prepare_func_exit",
"destroy_dynptrs_on_func_exit",
"destroy_if_dynptr_stack_slot"
],
"KMSANReasoning": "The patch modifies the BPF verifier in `kernel/bpf/verifier.c` by adding `destroy_dynptrs_on_func_exit()`, which is called during `prepare_func_exit()` to ensure that dynptrs allocated on a callee's stack frame are properly destructed and their derived slices invalidated when the subprogram returns.\n\nKMSAN vs KASAN applicability:\n- KMSAN detects reads of uninitialized memory (stack, heap, or page allocations) and uninitialized data leaks to user space.\n- KASAN and standard sanitizers detect memory safety violations such as use-after-free, out-of-bounds accesses, and logic bugs in kernel/verifier verification.\n\nThe changes in this patch:\n1. Operate purely within the BPF verifier's compile-time static analysis state machine (`bpf_func_state`).\n2. All local variables (`i`, `err`) and state accesses (`callee-\u003estack[i]`) are strictly initialized and bounded by `callee-\u003eallocated_stack / BPF_REG_SIZE`.\n3. Do not allocate or expose uninitialized memory, modify copy_to_user paths, or introduce conditional branches on uninitialized fields.\n\nBecause no uninitialized memory risks or kernel-to-user info-leaks are introduced or exposed, a dedicated KMSAN fuzzing session is not warranted.",
"NeedsKMSAN": false,
"Reasoning": "The patch modifies the BPF verifier (kernel/bpf/verifier.c) by introducing destroy_dynptrs_on_func_exit to tear down callee-local dynptrs and invalidate derived slices when exiting subprograms in prepare_func_exit. This touches reachable core subsystem verification logic executed during BPF program verification via sys_bpf.",
"WorthFuzzing": true
} |
| 1/1 | 2026/09/11 08:55 | action | read-patch-diff |
0mArgs:null Results: {
"PatchDiff": "commit 9a7ef57b145f9ca413ba86bde57c64d5949287c0\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Fri Sep 11 08:55:05 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c\nindex 72a3f5998dd27..c9c1df27b2699 100644\n--- a/kernel/bpf/verifier.c\n+++ b/kernel/bpf/verifier.c\n@@ -800,6 +800,31 @@ static int dynptr_ref_cnt(struct bpf_verifier_env *env, int v_parent_id)\n \treturn ref_cnt;\n }\n \n+static int destroy_dynptrs_on_func_exit(struct bpf_verifier_env *env,\n+\t\t\t\t\tstruct bpf_func_state *callee)\n+{\n+\tint i, err;\n+\n+\tfor (i = 0; i \u003c callee-\u003eallocated_stack / BPF_REG_SIZE; i++) {\n+\t\tstruct bpf_stack_state *slot = \u0026callee-\u003estack[i];\n+\n+\t\tif (slot-\u003eslot_type[0] != STACK_DYNPTR ||\n+\t\t !slot-\u003espilled_ptr.dynptr.first_slot)\n+\t\t\tcontinue;\n+\n+\t\t/*\n+\t\t * A callee-local dynptr is destroyed when its stack frame goes\n+\t\t * away. Apply the normal stack-slot teardown so references cannot\n+\t\t * be lost and slices derived from that dynptr are invalidated.\n+\t\t */\n+\t\terr = destroy_if_dynptr_stack_slot(env, callee, i);\n+\t\tif (err)\n+\t\t\treturn err;\n+\t}\n+\n+\treturn 0;\n+}\n+\n static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,\n \t\t\t\t struct bpf_func_state *state, int spi)\n {\n@@ -10399,6 +10424,9 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)\n \t\tprint_verifier_state(env, state, caller-\u003eframeno, true);\n \t}\n \taccount_processed_insns(env, callee, caller);\n+\terr = destroy_dynptrs_on_func_exit(env, callee);\n+\tif (err)\n+\t\treturn err;\n \t/* clear everything in the callee. In case of exceptional exits using\n \t * bpf_throw, this will be done by copy_verifier_state for extra frames. */\n \tfree_func_state(callee);\ndiff --git a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c\nindex 6dbd1487343c0..122ecb7e98e2a 100644\n--- a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c\n+++ b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c\n@@ -11,6 +11,7 @@\n #include \"bpf_qdisc_fail__invalid_dynptr.skel.h\"\n #include \"bpf_qdisc_fail__invalid_dynptr_slice.skel.h\"\n #include \"bpf_qdisc_fail__invalid_dynptr_cross_frame.skel.h\"\n+#include \"bpf_qdisc_fail__invalid_dynptr_returned_slice.skel.h\"\n #include \"bpf_qdisc_fail__untrusted_write.skel.h\"\n #include \"bpf_qdisc_dynptr_use_after_invalidate_clone.skel.h\"\n \n@@ -230,6 +231,7 @@ void test_ns_bpf_qdisc(void)\n \t\ttest_incompl_ops();\n \tRUN_TESTS(bpf_qdisc_fail__invalid_dynptr);\n \tRUN_TESTS(bpf_qdisc_fail__invalid_dynptr_cross_frame);\n+\tRUN_TESTS(bpf_qdisc_fail__invalid_dynptr_returned_slice);\n \tRUN_TESTS(bpf_qdisc_fail__invalid_dynptr_slice);\n \tRUN_TESTS(bpf_qdisc_fail__untrusted_write);\n \tRUN_TESTS(bpf_qdisc_dynptr_use_after_invalidate_clone);\ndiff --git a/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c\nnew file mode 100644\nindex 0000000000000..8217f4c4c00c4\n--- /dev/null\n+++ b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c\n@@ -0,0 +1,76 @@\n+// SPDX-License-Identifier: GPL-2.0\n+\n+#include \u003cvmlinux.h\u003e\n+#include \"bpf_experimental.h\"\n+#include \"bpf_qdisc_common.h\"\n+#include \"bpf_misc.h\"\n+\n+char _license[] SEC(\"license\") = \"GPL\";\n+\n+int proto;\n+\n+static __noinline struct ethhdr *slice_in_subprog(struct sk_buff *skb)\n+{\n+\tstruct bpf_dynptr ptr;\n+\n+\tbpf_dynptr_from_skb((struct __sk_buff *)skb, 0, \u0026ptr);\n+\treturn bpf_dynptr_slice(\u0026ptr, 0, NULL, sizeof(struct ethhdr));\n+}\n+\n+SEC(\"struct_ops\")\n+__failure __msg(\"invalid mem access 'scalar'\")\n+int BPF_PROG(invalid_dynptr_returned_slice, struct sk_buff *skb,\n+\t struct Qdisc *sch, struct bpf_sk_buff_ptr *to_free)\n+{\n+\tstruct ethhdr *hdr;\n+\n+\thdr = slice_in_subprog(skb);\n+\tif (!hdr) {\n+\t\tbpf_qdisc_skb_drop(skb, to_free);\n+\t\treturn NET_XMIT_DROP;\n+\t}\n+\n+\t/* this should fail */\n+\tproto = hdr-\u003eh_proto;\n+\n+\tbpf_qdisc_skb_drop(skb, to_free);\n+\n+\treturn NET_XMIT_DROP;\n+}\n+\n+SEC(\"struct_ops\")\n+__auxiliary\n+struct sk_buff *BPF_PROG(bpf_qdisc_test_dequeue, struct Qdisc *sch)\n+{\n+\treturn NULL;\n+}\n+\n+SEC(\"struct_ops\")\n+__auxiliary\n+int BPF_PROG(bpf_qdisc_test_init, struct Qdisc *sch, struct nlattr *opt,\n+\t struct netlink_ext_ack *extack)\n+{\n+\treturn 0;\n+}\n+\n+SEC(\"struct_ops\")\n+__auxiliary\n+void BPF_PROG(bpf_qdisc_test_reset, struct Qdisc *sch)\n+{\n+}\n+\n+SEC(\"struct_ops\")\n+__auxiliary\n+void BPF_PROG(bpf_qdisc_test_destroy, struct Qdisc *sch)\n+{\n+}\n+\n+SEC(\".struct_ops\")\n+struct Qdisc_ops test = {\n+\t.enqueue = (void *)invalid_dynptr_returned_slice,\n+\t.dequeue = (void *)bpf_qdisc_test_dequeue,\n+\t.init = (void *)bpf_qdisc_test_init,\n+\t.reset = (void *)bpf_qdisc_test_reset,\n+\t.destroy = (void *)bpf_qdisc_test_destroy,\n+\t.id = \"bpf_qdisc_test\",\n+};\ndiff --git a/tools/testing/selftests/bpf/progs/dynptr_fail.c b/tools/testing/selftests/bpf/progs/dynptr_fail.c\nindex 1cd61d72c166f..f57e6162dbf5b 100644\n--- a/tools/testing/selftests/bpf/progs/dynptr_fail.c\n+++ b/tools/testing/selftests/bpf/progs/dynptr_fail.c\n@@ -127,7 +127,7 @@ static int missing_release_callback_fn(__u32 index, void *data)\n \n /* Any dynptr initialized within a callback must have bpf_dynptr_put called */\n SEC(\"?raw_tp\")\n-__failure __msg(\"Unreleased reference id\")\n+__failure __msg(\"cannot overwrite referenced dynptr\")\n int ringbuf_missing_release_callback(void *ctx)\n {\n \tbpf_loop(10, missing_release_callback_fn, NULL, 0);\n@@ -1892,6 +1892,101 @@ int clone_invalidate4(void *ctx)\n \treturn 0;\n }\n \n+static __noinline void clone_slice_in_subprog(struct bpf_dynptr *ptr, int **data)\n+{\n+\tstruct bpf_dynptr clone;\n+\n+\tbpf_dynptr_clone(ptr, \u0026clone);\n+\t*data = bpf_dynptr_data(\u0026clone, 0, sizeof(val));\n+}\n+\n+static __noinline void caller_slice_in_subprog(struct bpf_dynptr *ptr, int **data)\n+{\n+\tstruct bpf_dynptr clone;\n+\n+\t*data = bpf_dynptr_data(ptr, 0, sizeof(val));\n+\tbpf_dynptr_clone(ptr, \u0026clone);\n+}\n+\n+static __noinline void reserve_dynptr_in_subprog(void)\n+{\n+\tstruct bpf_dynptr ptr;\n+\n+\tbpf_ringbuf_reserve_dynptr(\u0026ringbuf, val, 0, \u0026ptr);\n+}\n+\n+/* A subprogram cannot lose the last dynptr that can release a resource. */\n+SEC(\"?raw_tp\")\n+__failure __msg(\"cannot overwrite referenced dynptr\")\n+int referenced_dynptr_lost_on_subprog_return(void *ctx)\n+{\n+\treserve_dynptr_in_subprog();\n+\n+\treturn 0;\n+}\n+\n+/*\n+ * Destroying a local clone on return must not invalidate a slice whose\n+ * source dynptr belongs to the caller.\n+ */\n+SEC(\"?raw_tp\")\n+__success\n+int caller_dynptr_slice_across_subprog_valid(void *ctx)\n+{\n+\tstruct bpf_dynptr ptr;\n+\tint *data = NULL;\n+\n+\tbpf_ringbuf_reserve_dynptr(\u0026ringbuf, val, 0, \u0026ptr);\n+\tcaller_slice_in_subprog(\u0026ptr, \u0026data);\n+\tif (data)\n+\t\t*data = 123;\n+\tbpf_ringbuf_submit_dynptr(\u0026ptr, 0);\n+\n+\treturn 0;\n+}\n+\n+/*\n+ * A slice that escapes a clone's call frame is invalid once the local\n+ * clone is destroyed on return.\n+ */\n+SEC(\"?raw_tp\")\n+__failure __msg(\"invalid mem access 'scalar'\")\n+int clone_slice_returned_frame_invalid(void *ctx)\n+{\n+\tstruct bpf_dynptr ptr;\n+\tint *data = NULL;\n+\n+\tbpf_ringbuf_reserve_dynptr(\u0026ringbuf, val, 0, \u0026ptr);\n+\tclone_slice_in_subprog(\u0026ptr, \u0026data);\n+\tif (data)\n+\t\t/* this should fail */\n+\t\t*data = 123;\n+\tbpf_ringbuf_submit_dynptr(\u0026ptr, 0);\n+\n+\treturn 0;\n+}\n+\n+/*\n+ * Releasing the shared reservation must invalidate a slice that escaped\n+ * from a clone's call frame.\n+ */\n+SEC(\"?raw_tp\")\n+__failure __msg(\"invalid mem access 'scalar'\")\n+int clone_slice_returned_frame_release_invalid(void *ctx)\n+{\n+\tstruct bpf_dynptr ptr;\n+\tint *data = NULL;\n+\n+\tbpf_ringbuf_reserve_dynptr(\u0026ringbuf, val, 0, \u0026ptr);\n+\tclone_slice_in_subprog(\u0026ptr, \u0026data);\n+\tbpf_ringbuf_submit_dynptr(\u0026ptr, 0);\n+\tif (data)\n+\t\t/* this should fail */\n+\t\t*data = 123;\n+\n+\treturn 0;\n+}\n+\n /* Invalidating a dynptr should invalidate any data slices\n * of its parent\n */\n"
} |
| 2/1 | 2026/09/11 08:55 | agent | patch-evaluator |
0mModel:core Args: null Results: {
"EnableConfigs": [
"BPF_SYSCALL"
],
"FocusSymbols": [
"bpf_check",
"prepare_func_exit",
"destroy_dynptrs_on_func_exit",
"destroy_if_dynptr_stack_slot"
],
"Reasoning": "The patch modifies the BPF verifier (kernel/bpf/verifier.c) by introducing destroy_dynptrs_on_func_exit to tear down callee-local dynptrs and invalidate derived slices when exiting subprograms in prepare_func_exit. This touches reachable core subsystem verification logic executed during BPF program verification via sys_bpf.",
"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 9a7ef57b145f9ca413ba86bde57c64d5949287c0
Author: syz-cluster <triage@syzkaller.com>
Date: Fri Sep 11 08:55:05 2026 +0000
syz-cluster: applied patch under review
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 72a3f5998dd27..c9c1df27b2699 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -800,6 +800,31 @@ static int dynptr_ref_cnt(struct bpf_verifier_env *env, int v_parent_id)
return ref_cnt;
}
+static int destroy_dynptrs_on_func_exit(struct bpf_verifier_env *env,
+ struct bpf_func_state *callee)
+{
+ int i, err;
+
+ for (i = 0; i < callee->allocated_stack / BPF_REG_SIZE; i++) {
+ struct bpf_stack_state *slot = &callee->stack[i];
+
+ if (slot->slot_type[0] != STACK_DYNPTR ||
+ !slot->spilled_ptr.dynptr.first_slot)
+ continue;
+
+ /*
+ * A callee-local dynptr is destroyed when its stack frame goes
+ * away. Apply the normal stack-slot teardown so references cannot
+ * be lost and slices derived from that dynptr are invalidated.
+ */
+ err = destroy_if_dynptr_stack_slot(env, callee, i);
+ if (err)
+ return err;
+ }
+
+ return 0;
+}
+
static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,
struct bpf_func_state *state, int spi)
{
@@ -10399,6 +10424,9 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
print_verifier_state(env, state, caller->frameno, true);
}
account_processed_insns(env, callee, caller);
+ err = destroy_dynptrs_on_func_exit(env, callee);
+ if (err)
+ return err;
/* clear everything in the callee. In case of exceptional exits using
* bpf_throw, this will be done by copy_verifier_state for extra frames. */
free_func_state(callee);
diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
index 6dbd1487343c0..122ecb7e98e2a 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
@@ -11,6 +11,7 @@
#include "bpf_qdisc_fail__invalid_dynptr.skel.h"
#include "bpf_qdisc_fail__invalid_dynptr_slice.skel.h"
#include "bpf_qdisc_fail__invalid_dynptr_cross_frame.skel.h"
+#include "bpf_qdisc_fail__invalid_dynptr_returned_slice.skel.h"
#include "bpf_qdisc_fail__untrusted_write.skel.h"
#include "bpf_qdisc_dynptr_use_after_invalidate_clone.skel.h"
@@ -230,6 +231,7 @@ void test_ns_bpf_qdisc(void)
test_incompl_ops();
RUN_TESTS(bpf_qdisc_fail__invalid_dynptr);
RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_cross_frame);
+ RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_returned_slice);
RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_slice);
RUN_TESTS(bpf_qdisc_fail__untrusted_write);
RUN_TESTS(bpf_qdisc_dynptr_use_after_invalidate_clone);
diff --git a/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c
new file mode 100644
index 0000000000000..8217f4c4c00c4
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c
@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include "bpf_experimental.h"
+#include "bpf_qdisc_common.h"
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+int proto;
+
+static __noinline struct ethhdr *slice_in_subprog(struct sk_buff *skb)
+{
+ struct bpf_dynptr ptr;
+
+ bpf_dynptr_from_skb((struct __sk_buff *)skb, 0, &ptr);
+ return bpf_dynptr_slice(&ptr, 0, NULL, sizeof(struct ethhdr));
+}
+
+SEC("struct_ops")
+__failure __msg("invalid mem access 'scalar'")
+int BPF_PROG(invalid_dynptr_returned_slice, struct sk_buff *skb,
+ struct Qdisc *sch, struct bpf_sk_buff_ptr *to_free)
+{
+ struct ethhdr *hdr;
+
+ hdr = slice_in_subprog(skb);
+ if (!hdr) {
+ bpf_qdisc_skb_drop(skb, to_free);
+ return NET_XMIT_DROP;
+ }
+
+ /* this should fail */
+ proto = hdr->h_proto;
+
+ bpf_qdisc_skb_drop(skb, to_free);
+
+ return NET_XMIT_DROP;
+}
+
+SEC("struct_ops")
+__auxiliary
+struct sk_buff *BPF_PROG(bpf_qdisc_test_dequeue, struct Qdisc *sch)
+{
+ return NULL;
+}
+
+SEC("struct_ops")
+__auxiliary
+int BPF_PROG(bpf_qdisc_test_init, struct Qdisc *sch, struct nlattr *opt,
+ struct netlink_ext_ack *extack)
+{
+ return 0;
+}
+
+SEC("struct_ops")
+__auxiliary
+void BPF_PROG(bpf_qdisc_test_reset, struct Qdisc *sch)
+{
+}
+
+SEC("struct_ops")
+__auxiliary
+void BPF_PROG(bpf_qdisc_test_destroy, struct Qdisc *sch)
+{
+}
+
+SEC(".struct_ops")
+struct Qdisc_ops test = {
+ .enqueue = (void *)invalid_dynptr_returned_slice,
+ .dequeue = (void *)bpf_qdisc_test_dequeue,
+ .init = (void *)bpf_qdisc_test_init,
+ .reset = (void *)bpf_qdisc_test_reset,
+ .destroy = (void *)bpf_qdisc_test_destroy,
+ .id = "bpf_qdisc_test",
+};
diff --git a/tools/testing/selftests/bpf/progs/dynptr_fail.c b/tools/testing/selftests/bpf/progs/dynptr_fail.c
index 1cd61d72c166f..f57e6162dbf5b 100644
--- a/tools/testing/selftests/bpf/progs/dynptr_fail.c
+++ b/tools/testing/selftests/bpf/progs/dynptr_fail.c
@@ -127,7 +127,7 @@ static int missing_release_callback_fn(__u32 index, void *data)
/* Any dynptr initialized within a callback must have bpf_dynptr_put called */
SEC("?raw_tp")
-__failure __msg("Unreleased reference id")
+__failure __msg("cannot overwrite referenced dynptr")
int ringbuf_missing_release_callback(void *ctx)
{
bpf_loop(10, missing_release_callback_fn, NULL, 0);
@@ -1892,6 +1892,101 @@ int clone_invalidate4(void *ctx)
return 0;
}
+static __noinline void clone_slice_in_subprog(struct bpf_dynptr *ptr, int **data)
+{
+ struct bpf_dynptr clone;
+
+ bpf_dynptr_clone(ptr, &clone);
+ *data = bpf_dynptr_data(&clone, 0, sizeof(val));
+}
+
+static __noinline void caller_slice_in_subprog(struct bpf_dynptr *ptr, int **data)
+{
+ struct bpf_dynptr clone;
+
+ *data = bpf_dynptr_data(ptr, 0, sizeof(val));
+ bpf_dynptr_clone(ptr, &clone);
+}
+
+static __noinline void reserve_dynptr_in_subprog(void)
+{
+ struct bpf_dynptr ptr;
+
+ bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+}
+
+/* A subprogram cannot lose the last dynptr that can release a resource. */
+SEC("?raw_tp")
+__failure __msg("cannot overwrite referenced dynptr")
+int referenced_dynptr_lost_on_subprog_return(void *ctx)
+{
+ reserve_dynptr_in_subprog();
+
+ return 0;
+}
+
+/*
+ * Destroying a local clone on return must not invalidate a slice whose
+ * source dynptr belongs to the caller.
+ */
+SEC("?raw_tp")
+__success
+int caller_dynptr_slice_across_subprog_valid(void *ctx)
+{
+ struct bpf_dynptr ptr;
+ int *data = NULL;
+
+ bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+ caller_slice_in_subprog(&ptr, &data);
+ if (data)
+ *data = 123;
+ bpf_ringbuf_submit_dynptr(&ptr, 0);
+
+ return 0;
+}
+
+/*
+ * A slice that escapes a clone's call frame is invalid once the local
+ * clone is destroyed on return.
+ */
+SEC("?raw_tp")
+__failure __msg("invalid mem access 'scalar'")
+int clone_slice_returned_frame_invalid(void *ctx)
+{
+ struct bpf_dynptr ptr;
+ int *data = NULL;
+
+ bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+ clone_slice_in_subprog(&ptr, &data);
+ if (data)
+ /* this should fail */
+ *data = 123;
+ bpf_ringbuf_submit_dynptr(&ptr, 0);
+
+ return 0;
+}
+
+/*
+ * Releasing the shared reservation must invalidate a slice that escaped
+ * from a clone's call frame.
+ */
+SEC("?raw_tp")
+__failure __msg("invalid mem access 'scalar'")
+int clone_slice_returned_frame_release_invalid(void *ctx)
+{
+ struct bpf_dynptr ptr;
+ int *data = NULL;
+
+ bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+ clone_slice_in_subprog(&ptr, &data);
+ bpf_ringbuf_submit_dynptr(&ptr, 0);
+ if (data)
+ /* this should fail */
+ *data = 123;
+
+ return 0;
+}
+
/* Invalidating a dynptr should invalidate any data slices
* of its parent
*/
|
| 3/2 | 2026/09/11 08:55 | llm | patch-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 5885 output: 36 thoughts: 117 Thoughts: **Analyzing the BPF Verifier Patch** Okay, so this patch is digging into the heart of the BPF verifier, specifically `kernel/bpf/verifier.c`. My initial scan shows the addition of `destroy_dynptrs_on_func_exit` and its integration into `prepare_func_exit`. This immediately piques my interest; anything dealing with dynamic pointer management in the verifier is worth a close look. Memory safety, as always, is paramount in this area. We need to be airtight. My next move is to dive into the code. Time to fire up my tools – read-file or grepper will give me a comprehensive view of the surrounding code in `kernel/bpf/verifier.c`. I need to understand the *why* behind this change. What's the context? What problem is this function addressing, and how does it fit into the existing verifier logic? What are the implications for existing BPF programs? The presence of new tests in `tools/testing/selftests/bpf/` is a good sign. It suggests a focused effort on validating the changes. I'll need to examine those tests thoroughly to ensure they're adequately covering the new functionality and potential edge cases. This will be my next step after inspecting the core code changes. Verification is key. |
| 4/2 | 2026/09/11 08:55 | tool | grepper |
0mArgs:{
"Expression": "destroy_dynptrs_on_func_exit",
"PathPrefix": "kernel/bpf/"
}Results: {
"Output": "kernel/bpf/verifier.c=784=static int dynptr_ref_cnt(struct bpf_verifier_env *env, int v_parent_id)\n--\nkernel/bpf/verifier.c-802-\nkernel/bpf/verifier.c:803:static int destroy_dynptrs_on_func_exit(struct bpf_verifier_env *env,\nkernel/bpf/verifier.c-804-\t\t\t\t\tstruct bpf_func_state *callee)\n--\nkernel/bpf/verifier.c=10359=static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)\n--\nkernel/bpf/verifier.c-10426-\taccount_processed_insns(env, callee, caller);\nkernel/bpf/verifier.c:10427:\terr = destroy_dynptrs_on_func_exit(env, callee);\nkernel/bpf/verifier.c-10428-\tif (err)\n"
} |
| 5/2 | 2026/09/11 08:55 | llm | patch-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 6582 output: 36 thoughts: 37 Thoughts: Here's my summary, as though I'm processing this information: **Analyzing BPF Verifier Logic: Key Sections** Okay, so I need to dive into the BPF verifier code again. I'm going to focus on `kernel/bpf/verifier.c`. Let's zero in on a couple of critical sections. First, lines 790-840. I know this area probably deals with… *checks notes* …likely some aspect of register state tracking or perhaps constraint propagation, given the surrounding context. It could also involve a specific instruction-set check or potentially an early error-path handling routine for a particular instruction sequence. I'll need to scrutinize how it handles register liveness or address space mapping, assuming this code is still about memory boundaries for direct packet access. Next, I’ll need to switch gears, and quickly review lines 10420-10440. Ah, this looks like it could be within a much larger verification phase. Given the line number, I'd bet this is related to something deeper within the verifier's core logic. Maybe it's checking for loop invariants or maybe it's doing a final analysis of control flow paths before declaring the program safe. Perhaps it's dealing with a tricky edge case, like validating indirect jumps or memory accesses within loops. Time to get my hands dirty. I'll focus on these two chunks and see where they get me. This should give me a solid feel for the current implementation and any potential areas that need improvement or optimization in the context of recent patches. |
| 6/2 | 2026/09/11 08:55 | tool | read-file |
0mArgs:{
"File": "kernel/bpf/verifier.c",
"FirstLine": 795,
"LineCount": 50
}Results: {
"Contents": " 795:\t\t\t\tcontinue;\n 796:\t\t\tif (stack-\u003espilled_ptr.parent_id == v_parent_id)\n 797:\t\t\t\tref_cnt++;\n 798:\t\t}));\n 799:\t\n 800:\t\treturn ref_cnt;\n 801:\t}\n 802:\t\n 803:\tstatic int destroy_dynptrs_on_func_exit(struct bpf_verifier_env *env,\n 804:\t\t\t\t\t\tstruct bpf_func_state *callee)\n 805:\t{\n 806:\t\tint i, err;\n 807:\t\n 808:\t\tfor (i = 0; i \u003c callee-\u003eallocated_stack / BPF_REG_SIZE; i++) {\n 809:\t\t\tstruct bpf_stack_state *slot = \u0026callee-\u003estack[i];\n 810:\t\n 811:\t\t\tif (slot-\u003eslot_type[0] != STACK_DYNPTR ||\n 812:\t\t\t !slot-\u003espilled_ptr.dynptr.first_slot)\n 813:\t\t\t\tcontinue;\n 814:\t\n 815:\t\t\t/*\n 816:\t\t\t * A callee-local dynptr is destroyed when its stack frame goes\n 817:\t\t\t * away. Apply the normal stack-slot teardown so references cannot\n 818:\t\t\t * be lost and slices derived from that dynptr are invalidated.\n 819:\t\t\t */\n 820:\t\t\terr = destroy_if_dynptr_stack_slot(env, callee, i);\n 821:\t\t\tif (err)\n 822:\t\t\t\treturn err;\n 823:\t\t}\n 824:\t\n 825:\t\treturn 0;\n 826:\t}\n 827:\t\n 828:\tstatic int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,\n 829:\t\t\t\t\t struct bpf_func_state *state, int spi)\n 830:\t{\n 831:\t\tint err = 0;\n 832:\t\n 833:\t\t/* We always ensure that STACK_DYNPTR is never set partially,\n 834:\t\t * hence just checking for slot_type[0] is enough. This is\n 835:\t\t * different for STACK_SPILL, where it may be only set for\n 836:\t\t * 1 byte, so code has to use is_spilled_reg.\n 837:\t\t */\n 838:\t\tif (state-\u003estack[spi].slot_type[0] != STACK_DYNPTR)\n 839:\t\t\treturn 0;\n 840:\t\n 841:\t\t/* Reposition spi to first slot */\n 842:\t\tif (!state-\u003estack[spi].spilled_ptr.dynptr.first_slot)\n 843:\t\t\tspi = spi + 1;\n 844:\t\n"
} |
| 7/2 | 2026/09/11 08:55 | llm | patch-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 7755 output: 38 thoughts: 20 Thoughts: Here's a summary of my thought process, as requested: **Navigating a Complex Codebase** Okay, time to dive in. I need to refresh my memory on the handling of function exits, particularly the `prepare_func_exit` function. Based on my existing knowledge of this codebase, my instinct is to look around line 10420. This is probably a good starting point, given the context of what I'm currently working on, and likely where I will find the information I need. I'll need to understand the exit procedure to verify the behavior I am expecting. |
| 8/2 | 2026/09/11 08:55 | tool | read-file |
0mArgs:{
"File": "kernel/bpf/verifier.c",
"FirstLine": 10415,
"LineCount": 35
}Results: {
"Contents": "10415:\t\tif (in_callback_fn)\n10416:\t\t\t*insn_idx = callee-\u003ecallsite;\n10417:\t\telse\n10418:\t\t\t*insn_idx = callee-\u003ecallsite + 1;\n10419:\t\n10420:\t\tif (env-\u003elog.level \u0026 BPF_LOG_LEVEL) {\n10421:\t\t\tverbose(env, \"returning from callee:\\n\");\n10422:\t\t\tprint_verifier_state(env, state, callee-\u003eframeno, true);\n10423:\t\t\tverbose(env, \"to caller at %d:\\n\", *insn_idx);\n10424:\t\t\tprint_verifier_state(env, state, caller-\u003eframeno, true);\n10425:\t\t}\n10426:\t\taccount_processed_insns(env, callee, caller);\n10427:\t\terr = destroy_dynptrs_on_func_exit(env, callee);\n10428:\t\tif (err)\n10429:\t\t\treturn err;\n10430:\t\t/* clear everything in the callee. In case of exceptional exits using\n10431:\t\t * bpf_throw, this will be done by copy_verifier_state for extra frames. */\n10432:\t\tfree_func_state(callee);\n10433:\t\tstate-\u003eframe[state-\u003ecurframe--] = NULL;\n10434:\t\tinvalidate_outgoing_stack_args(env, caller);\n10435:\t\n10436:\t\t/* for callbacks widen imprecise scalars to make programs like below verify:\n10437:\t\t *\n10438:\t\t * struct ctx { int i; }\n10439:\t\t * void cb(int idx, struct ctx *ctx) { ctx-\u003ei++; ... }\n10440:\t\t * ...\n10441:\t\t * struct ctx = { .i = 0; }\n10442:\t\t * bpf_loop(100, cb, \u0026ctx, 0);\n10443:\t\t *\n10444:\t\t * This is similar to what is done in process_iter_next_call() for open\n10445:\t\t * coded iterators.\n10446:\t\t */\n10447:\t\tprev_st = in_callback_fn ? find_prev_entry(env, state, *insn_idx) : NULL;\n10448:\t\tif (prev_st) {\n10449:\t\t\terr = widen_imprecise_scalars(env, prev_st, state);\n"
} |
| 9/2 | 2026/09/11 08:55 | llm | patch-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 8617 output: 28 thoughts: 194 Thoughts: **My Assessment of the BPF Verifier Change** Okay, so this patch is touching the BPF verifier logic, specifically in `kernel/bpf/verifier.c`. Immediately, my brain flags this as important. The verifier is a core piece of the BPF subsystem, and we all know how heavily syzkaller targets that area through the `bpf()` syscall and the `BPF_PROG_LOAD` command. So, the question arises – is this change fuzz-worthy? Absolutely, yes. The fact that the changes are within `kernel/bpf/verifier.c` and modify code related to subprogram returns and function exits – essentially, where the `BPF_EXIT` instruction and the `prepare_func_exit` function come into play – suggests there's potentially reachable code. This specific addition deals with teardown logic for stack dynamic pointers (`dynptrs`) on function exit, calling `destroy_dynptrs_on_func_exit` and `destroy_if_dynptr_stack_slot`. That smells like a new attack surface, or at least a place where subtle interactions could lead to vulnerabilities. Now, I need to check the Kconfig to see what configurations are necessary to enable this area of the code. Let's make sure the BPF subsystem and the `BPF_SYSCALL` option are enabled. I also need to verify the relevant sections in the `kernel/bpf/verifier.c` Kconfig file to ensure the specific code paths are enabled. |
| 10/2 | 2026/09/11 08:55 | tool | grepper |
0mArgs:{
"Expression": "verifier\\.o",
"PathPrefix": "kernel/bpf/"
}Results: {
"Output": "kernel/bpf/Makefile=7=CFLAGS_core.o += -Wno-override-init $(cflags-nogcse-yy)\nkernel/bpf/Makefile-8-\nkernel/bpf/Makefile:9:obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o cnum.o log.o token.o liveness.o const_fold.o diagnostics.o\nkernel/bpf/Makefile-10-obj-$(CONFIG_BPF_SYSCALL) += bpf_iter.o map_iter.o task_iter.o prog_iter.o link_iter.o\n"
} |
| 11/2 | 2026/09/11 08:55 | llm | patch-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 9326 output: 29 thoughts: 29 Thoughts: Here's my take on the thought process, as if it were my own: **Investigating BPF Syscall Configuration** Alright, I need to pinpoint where the `BPF_SYSCALL` configuration option is defined. Knowing the kernel's Kconfig structure like the back of my hand, my first instinct is to check either `init/Kconfig` or `kernel/bpf/Kconfig`. Those are the two most logical places to start looking for a BPF-related setting. It's almost certain it'll be in one of those, or perhaps cross-referenced between them. This is the starting point for understanding how the BPF syscall feature is enabled or disabled at build time. |
| 12/2 | 2026/09/11 08:55 | tool | grepper |
0mError:no matches Args: {
"Expression": "config BPF_SYSCALL",
"PathPrefix": "init/"
}Results: {
"error": "no matches"
} |
| 13/2 | 2026/09/11 08:55 | llm | patch-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 9547 output: 21 thoughts: 15 Thoughts: Here's your summary, as if I were thinking it: **Digging Through Kconfigs: BPF_SYSCALL Hunt** Okay, so I need to track down where the `BPF_SYSCALL` configuration option is defined within the Kconfig files. This is a common task, but it’s critical for understanding how a feature like BPF syscall support is enabled or disabled and how it's integrated across the kernel build process. I need to quickly identify all the dependencies, any default values, and importantly, where this configuration is *used*. I can't afford to waste time manually grep-ing through every Kconfig file; I need a targeted and efficient approach. Let’s get to it. Time to explore. |
| 14/2 | 2026/09/11 08:55 | tool | grepper |
0mArgs:{
"Expression": "config BPF_SYSCALL"
}Results: {
"Output": "kernel/bpf/Kconfig=25=menu \"BPF subsystem\"\nkernel/bpf/Kconfig-26-\nkernel/bpf/Kconfig:27:config BPF_SYSCALL\nkernel/bpf/Kconfig-28-\tbool \"Enable bpf() system call\"\n"
} |
| 15/2 | 2026/09/11 08:55 | llm | patch-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 9822 output: 34 thoughts: 19 Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience: **Examining BPF Kconfig Configuration** Okay, I need to dive into the kernel's BPF configuration. My initial instinct is to go straight to `kernel/bpf/Kconfig`, specifically around line 27. I'm probably looking for the core BPF feature enablement flag, or maybe I'm trying to recall a related option that I want to double-check. Could be an experimental feature flag, or something tied to a specific BPF helper version. I suspect line 27 will likely lead me to the main entry point or a crucial dependency in that Kconfig file. I am hoping to get to the root cause of an issue I'm working through. I'm expecting this to provide the base configuration that all further configuration is reliant on. Time to see what's there and refresh my memory on the build options. |
| 16/2 | 2026/09/11 08:55 | tool | read-file |
0mArgs:{
"File": "kernel/bpf/Kconfig",
"FirstLine": 25,
"LineCount": 20
}Results: {
"Contents": " 25:\tmenu \"BPF subsystem\"\n 26:\t\n 27:\tconfig BPF_SYSCALL\n 28:\t\tbool \"Enable bpf() system call\"\n 29:\t\tselect BPF\n 30:\t\tselect IRQ_WORK\n 31:\t\tselect NEED_TASKS_RCU\n 32:\t\tselect TASKS_TRACE_RCU\n 33:\t\tselect BINARY_PRINTF\n 34:\t\tselect NET_SOCK_MSG if NET\n 35:\t\tselect NET_XGRESS if NET\n 36:\t\tselect PAGE_POOL if NET\n 37:\t\tdefault n\n 38:\t\thelp\n 39:\t\t Enable the bpf() system call that allows to manipulate BPF programs\n 40:\t\t and maps via file descriptors.\n 41:\t\n 42:\tconfig BPF_JIT\n 43:\t\tbool \"Enable BPF Just In Time compiler\"\n 44:\t\tdepends on BPF\n"
} |
| 17/2 | 2026/09/11 08:55 | llm | patch-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 10322 output: 30 thoughts: 196 Thoughts: **Analyzing BPF Verifier Functionality** Okay, let's dive into this BPF verifier code and see where we're at with these recent modifications. First, I need to get a clear picture of the core functions involved, focusing on the ones that have been added or significantly altered. The key symbols seem to be `destroy_dynptrs_on_func_exit`, `prepare_func_exit`, `destroy_if_dynptr_stack_slot`, and `bpf_check` (or potentially `do_check` or `check_cfg`, depending on the level of abstraction). Right, so `destroy_dynptrs_on_func_exit` is static; good, that keeps things relatively contained. `prepare_func_exit` is also static, and it looks like it’s called within `do_check`. That's important to note, and `destroy_if_dynptr_stack_slot` is also static and is also called when stack slots are overwritten. Okay, that's solidifying the picture a bit. Now, what about the non-static functions, are there any feature-specific symbols that might be impacting things? Now, to get a solid grasp of how these functions are being used in practice, I need to check the callers of `prepare_func_exit` and `destroy_if_dynptr_stack_slot` within `kernel/bpf/verifier.c`. Let's see how they integrate with the broader verification process. That will give me a better handle on the overall impact of these additions. |
| 18/2 | 2026/09/11 08:55 | tool | grepper |
0mArgs:{
"Expression": "prepare_func_exit",
"PathPrefix": "kernel/bpf/"
}Results: {
"Output": "kernel/bpf/verifier.c=10351=static bool retval_range_within(struct bpf_retval_range range, const struct bpf_reg_state *reg)\n--\nkernel/bpf/verifier.c-10358-\nkernel/bpf/verifier.c:10359:static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)\nkernel/bpf/verifier.c-10360-{\n--\nkernel/bpf/verifier.c=10841=static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,\n--\nkernel/bpf/verifier.c-11343-\t\t\t * frame. A callback frame cannot be left that way because\nkernel/bpf/verifier.c:11344:\t\t\t * prepare_func_exit() would apply its return contract to the\nkernel/bpf/verifier.c-11345-\t\t\t * unknown R0 synthesized below. Stack-depth validation rejects\n--\nkernel/bpf/verifier.c-11357-\t\t\tmark_reg_unknown(env, regs, BPF_REG_0);\nkernel/bpf/verifier.c:11358:\t\t\terr = prepare_func_exit(env, \u0026env-\u003einsn_idx);\nkernel/bpf/verifier.c-11359-\t\t\tif (err)\n--\nkernel/bpf/verifier.c=17316=static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn)\n--\nkernel/bpf/verifier.c-17396-\t\tmark_reg_known_zero(env, regs, BPF_REG_0);\nkernel/bpf/verifier.c:17397:\t\terr = prepare_func_exit(env, \u0026env-\u003einsn_idx);\nkernel/bpf/verifier.c-17398-\t\tif (err)\n--\nkernel/bpf/verifier.c=18103=static int process_bpf_exit_full(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-18109-\t/* We must do check_reference_leak here before\nkernel/bpf/verifier.c:18110:\t * prepare_func_exit to handle the case when\nkernel/bpf/verifier.c-18111-\t * state-\u003ecurframe \u003e 0, it may be a callback function,\n--\nkernel/bpf/verifier.c-18121-\nkernel/bpf/verifier.c:18122:\t/* The side effect of the prepare_func_exit which is\nkernel/bpf/verifier.c-18123-\t * being skipped is that it frees bpf_func_state.\n--\nkernel/bpf/verifier.c-18135-\t\t/* exit from nested function */\nkernel/bpf/verifier.c:18136:\t\terr = prepare_func_exit(env, \u0026env-\u003einsn_idx);\nkernel/bpf/verifier.c-18137-\t\tif (err)\n"
} |
| 19/2 | 2026/09/11 08:55 | llm | patch-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 11672 output: 31 thoughts: 35 Thoughts: Here's my take on the thought process, as if it were my own: **Diving into the BPF Verifier** Alright, let's get down to brass tacks. I'm focusing in on the BPF verifier, and the first thing I need to pin down is the main entry point. Right, that's `bpf_check` - it's the gatekeeper, located squarely in `kernel/bpf/verifier.c`. Now, my next move is obvious: I need to delve into the definition of `bpf_check`. I need to understand exactly what it's doing, how it orchestrates the verification process, and what initial checks it performs. No point in wasting time; let's get into the details of the function itself! |
| 20/2 | 2026/09/11 08:55 | tool | grepper |
0mArgs:{
"Expression": "int bpf_check\\(",
"PathPrefix": "kernel/bpf/"
}Results: {
"Output": "kernel/bpf/verifier.c=21043=static int bpf_prog_verify_signature(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-21159-\nkernel/bpf/verifier.c:21160:int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,\nkernel/bpf/verifier.c-21161-\t struct bpf_log_attr *attr_log)\n"
} |
| 21/2 | 2026/09/11 08:55 | llm | patch-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 12048 output: 35 thoughts: 27 Thoughts: Here's my summary, as though I'm thinking through this process: **Diving into `destroy_if_dynptr_stack_slot` in `verifier.c`** Okay, so I need to understand how we're using `destroy_if_dynptr_stack_slot` and related symbols within the verifier. It's time to dig into the calls to that function, or anything else that might be associated with it in `verifier.c`. My focus is to gain a deeper understanding of the memory management strategies for dynamic pointer stack slots within the verification process. I'll need to trace the flow, identifying potential areas of concern or points where we might be seeing performance bottlenecks or possible vulnerabilities. I'll also be looking for opportunities to optimize or improve the implementation of dynamic pointer management. |
| 22/2 | 2026/09/11 08:56 | tool | grepper |
0mArgs:{
"Expression": "destroy_if_dynptr_stack_slot",
"PathPrefix": "kernel/bpf/"
}Results: {
"Output": "kernel/bpf/states.c=398=static void __clean_func_state(struct bpf_verifier_env *env,\n--\nkernel/bpf/states.c-428-\t\t\t * Don't clear special slots.\nkernel/bpf/states.c:429:\t\t\t * destroy_if_dynptr_stack_slot() needs STACK_DYNPTR to\nkernel/bpf/states.c-430-\t\t\t * detect overwrites and invalidate associated data slices.\n--\nkernel/bpf/verifier.c=661=static void mark_dynptr_cb_reg(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-667-\nkernel/bpf/verifier.c:668:static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,\nkernel/bpf/verifier.c-669-\t\t\t\t struct bpf_func_state *state, int spi);\n--\nkernel/bpf/verifier.c=671=static int mark_stack_slots_dynptr(struct bpf_verifier_env *env, struct bpf_reg_state *reg,\n--\nkernel/bpf/verifier.c-683-\t/* We cannot assume both spi and spi - 1 belong to the same dynptr,\nkernel/bpf/verifier.c:684:\t * hence we need to call destroy_if_dynptr_stack_slot twice for both,\nkernel/bpf/verifier.c-685-\t * to ensure that for the following example:\n--\nkernel/bpf/verifier.c-691-\t */\nkernel/bpf/verifier.c:692:\terr = destroy_if_dynptr_stack_slot(env, state, spi);\nkernel/bpf/verifier.c-693-\tif (err)\nkernel/bpf/verifier.c-694-\t\treturn err;\nkernel/bpf/verifier.c:695:\terr = destroy_if_dynptr_stack_slot(env, state, spi - 1);\nkernel/bpf/verifier.c-696-\tif (err)\n--\nkernel/bpf/verifier.c=803=static int destroy_dynptrs_on_func_exit(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-819-\t\t */\nkernel/bpf/verifier.c:820:\t\terr = destroy_if_dynptr_stack_slot(env, callee, i);\nkernel/bpf/verifier.c-821-\t\tif (err)\n--\nkernel/bpf/verifier.c-827-\nkernel/bpf/verifier.c:828:static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,\nkernel/bpf/verifier.c-829-\t\t\t\t struct bpf_func_state *state, int spi)\n--\nkernel/bpf/verifier.c=870=static bool is_dynptr_reg_valid_uninit(struct bpf_verifier_env *env, struct bpf_reg_state *reg)\n--\nkernel/bpf/verifier.c-888-\t * STACK_DYNPTR slots, see mark_stack_slots_dynptr which calls\nkernel/bpf/verifier.c:889:\t * destroy_if_dynptr_stack_slot to ensure dynptr objects at the slots we are\nkernel/bpf/verifier.c-890-\t * touching are completely destructed before we reinitialize them for a new\nkernel/bpf/verifier.c:891:\t * one. For referenced ones, destroy_if_dynptr_stack_slot returns an error early\nkernel/bpf/verifier.c-892-\t * instead of delaying it until the end where the user will get \"Unreleased\n--\nkernel/bpf/verifier.c=3541=static int check_stack_write_fixed_off(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-3593-\nkernel/bpf/verifier.c:3594:\terr = destroy_if_dynptr_stack_slot(env, state, spi);\nkernel/bpf/verifier.c-3595-\tif (err)\n--\nkernel/bpf/verifier.c=3684=static int check_stack_write_var_off(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-3713-\t\tspi = bpf_get_spi(i);\nkernel/bpf/verifier.c:3714:\t\terr = destroy_if_dynptr_stack_slot(env, state, spi);\nkernel/bpf/verifier.c-3715-\t\tif (err)\n"
} |
| 23/2 | 2026/09/11 08:56 | llm | patch-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 13463 output: 155 thoughts: 203 Thoughts: **My Assessment of the BPF Verifier Patch** Okay, so I've looked over this patch, and here's my take: this is absolutely something we need to prioritize fuzzing. My initial instinct is "worth fuzzing," and after a deeper dive, I'm confident in that assessment. It looks like the core of this patch centers around proper cleanup and validation within the BPF verifier, specifically around how it handles dynamic pointers, or "dynptrs," when a subprogram exits. We're talking about crucial memory management and validation within a highly sensitive kernel subsystem. Any misstep here could lead to exploitable vulnerabilities. I've zeroed in on the key symbols this patch touches: `bpf_check`, `prepare_func_exit`, `destroy_dynptrs_on_func_exit`, and `destroy_if_dynptr_stack_slot`. These are the functions responsible for crucial aspects of the verifier's operation. I want to pay particularly close attention to how they interact and how the modifications might introduce unexpected edge cases. To make sure we're covering our bases, I need to confirm we're including `CONFIG_BPF_SYSCALL` in the enable configs. This is the main switch that turns on the BPF system and verifier. Without it, none of this is relevant. So, to summarize succinctly: This patch modifies BPF verifier logic to correctly handle the destruction of callee-local dynamic pointers and invalidate slices when a subprogram exits, thus making this a prime target for fuzzing. We should immediately call `set-results` to record this information! |
| 24/2 | 2026/09/11 08:56 | tool | set-results |
0mArgs:{
"EnableConfigs": [
"BPF_SYSCALL"
],
"FocusSymbols": [
"bpf_check",
"prepare_func_exit",
"destroy_dynptrs_on_func_exit",
"destroy_if_dynptr_stack_slot"
],
"Reasoning": "The patch modifies the BPF verifier (kernel/bpf/verifier.c) by introducing destroy_dynptrs_on_func_exit to tear down callee-local dynptrs and invalidate derived slices when exiting subprograms in prepare_func_exit. This touches reachable core subsystem verification logic executed during BPF program verification via sys_bpf.",
"WorthFuzzing": true
}Results: {
"EnableConfigs": [
"BPF_SYSCALL"
],
"FocusSymbols": [
"bpf_check",
"prepare_func_exit",
"destroy_dynptrs_on_func_exit",
"destroy_if_dynptr_stack_slot"
],
"Reasoning": "The patch modifies the BPF verifier (kernel/bpf/verifier.c) by introducing destroy_dynptrs_on_func_exit to tear down callee-local dynptrs and invalidate derived slices when exiting subprograms in prepare_func_exit. This touches reachable core subsystem verification logic executed during BPF program verification via sys_bpf.",
"WorthFuzzing": true
} |
| 25/1 | 2026/09/11 08:56 | action | If |
0mArgs:{
"WorthFuzzing": true
}Results: null |
| 26/2 | 2026/09/11 08:56 | agent | kmsan-evaluator |
0mModel:core Args: null Results: {
"KMSANReasoning": "The patch modifies the BPF verifier in `kernel/bpf/verifier.c` by adding `destroy_dynptrs_on_func_exit()`, which is called during `prepare_func_exit()` to ensure that dynptrs allocated on a callee's stack frame are properly destructed and their derived slices invalidated when the subprogram returns.\n\nKMSAN vs KASAN applicability:\n- KMSAN detects reads of uninitialized memory (stack, heap, or page allocations) and uninitialized data leaks to user space.\n- KASAN and standard sanitizers detect memory safety violations such as use-after-free, out-of-bounds accesses, and logic bugs in kernel/verifier verification.\n\nThe changes in this patch:\n1. Operate purely within the BPF verifier's compile-time static analysis state machine (`bpf_func_state`).\n2. All local variables (`i`, `err`) and state accesses (`callee-\u003estack[i]`) are strictly initialized and bounded by `callee-\u003eallocated_stack / BPF_REG_SIZE`.\n3. Do not allocate or expose uninitialized memory, modify copy_to_user paths, or introduce conditional branches on uninitialized fields.\n\nBecause no uninitialized memory risks or kernel-to-user info-leaks are introduced or exposed, a dedicated KMSAN fuzzing session is not warranted.",
"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 9a7ef57b145f9ca413ba86bde57c64d5949287c0
Author: syz-cluster <triage@syzkaller.com>
Date: Fri Sep 11 08:55:05 2026 +0000
syz-cluster: applied patch under review
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 72a3f5998dd27..c9c1df27b2699 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -800,6 +800,31 @@ static int dynptr_ref_cnt(struct bpf_verifier_env *env, int v_parent_id)
return ref_cnt;
}
+static int destroy_dynptrs_on_func_exit(struct bpf_verifier_env *env,
+ struct bpf_func_state *callee)
+{
+ int i, err;
+
+ for (i = 0; i < callee->allocated_stack / BPF_REG_SIZE; i++) {
+ struct bpf_stack_state *slot = &callee->stack[i];
+
+ if (slot->slot_type[0] != STACK_DYNPTR ||
+ !slot->spilled_ptr.dynptr.first_slot)
+ continue;
+
+ /*
+ * A callee-local dynptr is destroyed when its stack frame goes
+ * away. Apply the normal stack-slot teardown so references cannot
+ * be lost and slices derived from that dynptr are invalidated.
+ */
+ err = destroy_if_dynptr_stack_slot(env, callee, i);
+ if (err)
+ return err;
+ }
+
+ return 0;
+}
+
static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,
struct bpf_func_state *state, int spi)
{
@@ -10399,6 +10424,9 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
print_verifier_state(env, state, caller->frameno, true);
}
account_processed_insns(env, callee, caller);
+ err = destroy_dynptrs_on_func_exit(env, callee);
+ if (err)
+ return err;
/* clear everything in the callee. In case of exceptional exits using
* bpf_throw, this will be done by copy_verifier_state for extra frames. */
free_func_state(callee);
diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
index 6dbd1487343c0..122ecb7e98e2a 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
@@ -11,6 +11,7 @@
#include "bpf_qdisc_fail__invalid_dynptr.skel.h"
#include "bpf_qdisc_fail__invalid_dynptr_slice.skel.h"
#include "bpf_qdisc_fail__invalid_dynptr_cross_frame.skel.h"
+#include "bpf_qdisc_fail__invalid_dynptr_returned_slice.skel.h"
#include "bpf_qdisc_fail__untrusted_write.skel.h"
#include "bpf_qdisc_dynptr_use_after_invalidate_clone.skel.h"
@@ -230,6 +231,7 @@ void test_ns_bpf_qdisc(void)
test_incompl_ops();
RUN_TESTS(bpf_qdisc_fail__invalid_dynptr);
RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_cross_frame);
+ RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_returned_slice);
RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_slice);
RUN_TESTS(bpf_qdisc_fail__untrusted_write);
RUN_TESTS(bpf_qdisc_dynptr_use_after_invalidate_clone);
diff --git a/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c
new file mode 100644
index 0000000000000..8217f4c4c00c4
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c
@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include "bpf_experimental.h"
+#include "bpf_qdisc_common.h"
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+int proto;
+
+static __noinline struct ethhdr *slice_in_subprog(struct sk_buff *skb)
+{
+ struct bpf_dynptr ptr;
+
+ bpf_dynptr_from_skb((struct __sk_buff *)skb, 0, &ptr);
+ return bpf_dynptr_slice(&ptr, 0, NULL, sizeof(struct ethhdr));
+}
+
+SEC("struct_ops")
+__failure __msg("invalid mem access 'scalar'")
+int BPF_PROG(invalid_dynptr_returned_slice, struct sk_buff *skb,
+ struct Qdisc *sch, struct bpf_sk_buff_ptr *to_free)
+{
+ struct ethhdr *hdr;
+
+ hdr = slice_in_subprog(skb);
+ if (!hdr) {
+ bpf_qdisc_skb_drop(skb, to_free);
+ return NET_XMIT_DROP;
+ }
+
+ /* this should fail */
+ proto = hdr->h_proto;
+
+ bpf_qdisc_skb_drop(skb, to_free);
+
+ return NET_XMIT_DROP;
+}
+
+SEC("struct_ops")
+__auxiliary
+struct sk_buff *BPF_PROG(bpf_qdisc_test_dequeue, struct Qdisc *sch)
+{
+ return NULL;
+}
+
+SEC("struct_ops")
+__auxiliary
+int BPF_PROG(bpf_qdisc_test_init, struct Qdisc *sch, struct nlattr *opt,
+ struct netlink_ext_ack *extack)
+{
+ return 0;
+}
+
+SEC("struct_ops")
+__auxiliary
+void BPF_PROG(bpf_qdisc_test_reset, struct Qdisc *sch)
+{
+}
+
+SEC("struct_ops")
+__auxiliary
+void BPF_PROG(bpf_qdisc_test_destroy, struct Qdisc *sch)
+{
+}
+
+SEC(".struct_ops")
+struct Qdisc_ops test = {
+ .enqueue = (void *)invalid_dynptr_returned_slice,
+ .dequeue = (void *)bpf_qdisc_test_dequeue,
+ .init = (void *)bpf_qdisc_test_init,
+ .reset = (void *)bpf_qdisc_test_reset,
+ .destroy = (void *)bpf_qdisc_test_destroy,
+ .id = "bpf_qdisc_test",
+};
diff --git a/tools/testing/selftests/bpf/progs/dynptr_fail.c b/tools/testing/selftests/bpf/progs/dynptr_fail.c
index 1cd61d72c166f..f57e6162dbf5b 100644
--- a/tools/testing/selftests/bpf/progs/dynptr_fail.c
+++ b/tools/testing/selftests/bpf/progs/dynptr_fail.c
@@ -127,7 +127,7 @@ static int missing_release_callback_fn(__u32 index, void *data)
/* Any dynptr initialized within a callback must have bpf_dynptr_put called */
SEC("?raw_tp")
-__failure __msg("Unreleased reference id")
+__failure __msg("cannot overwrite referenced dynptr")
int ringbuf_missing_release_callback(void *ctx)
{
bpf_loop(10, missing_release_callback_fn, NULL, 0);
@@ -1892,6 +1892,101 @@ int clone_invalidate4(void *ctx)
return 0;
}
+static __noinline void clone_slice_in_subprog(struct bpf_dynptr *ptr, int **data)
+{
+ struct bpf_dynptr clone;
+
+ bpf_dynptr_clone(ptr, &clone);
+ *data = bpf_dynptr_data(&clone, 0, sizeof(val));
+}
+
+static __noinline void caller_slice_in_subprog(struct bpf_dynptr *ptr, int **data)
+{
+ struct bpf_dynptr clone;
+
+ *data = bpf_dynptr_data(ptr, 0, sizeof(val));
+ bpf_dynptr_clone(ptr, &clone);
+}
+
+static __noinline void reserve_dynptr_in_subprog(void)
+{
+ struct bpf_dynptr ptr;
+
+ bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+}
+
+/* A subprogram cannot lose the last dynptr that can release a resource. */
+SEC("?raw_tp")
+__failure __msg("cannot overwrite referenced dynptr")
+int referenced_dynptr_lost_on_subprog_return(void *ctx)
+{
+ reserve_dynptr_in_subprog();
+
+ return 0;
+}
+
+/*
+ * Destroying a local clone on return must not invalidate a slice whose
+ * source dynptr belongs to the caller.
+ */
+SEC("?raw_tp")
+__success
+int caller_dynptr_slice_across_subprog_valid(void *ctx)
+{
+ struct bpf_dynptr ptr;
+ int *data = NULL;
+
+ bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+ caller_slice_in_subprog(&ptr, &data);
+ if (data)
+ *data = 123;
+ bpf_ringbuf_submit_dynptr(&ptr, 0);
+
+ return 0;
+}
+
+/*
+ * A slice that escapes a clone's call frame is invalid once the local
+ * clone is destroyed on return.
+ */
+SEC("?raw_tp")
+__failure __msg("invalid mem access 'scalar'")
+int clone_slice_returned_frame_invalid(void *ctx)
+{
+ struct bpf_dynptr ptr;
+ int *data = NULL;
+
+ bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+ clone_slice_in_subprog(&ptr, &data);
+ if (data)
+ /* this should fail */
+ *data = 123;
+ bpf_ringbuf_submit_dynptr(&ptr, 0);
+
+ return 0;
+}
+
+/*
+ * Releasing the shared reservation must invalidate a slice that escaped
+ * from a clone's call frame.
+ */
+SEC("?raw_tp")
+__failure __msg("invalid mem access 'scalar'")
+int clone_slice_returned_frame_release_invalid(void *ctx)
+{
+ struct bpf_dynptr ptr;
+ int *data = NULL;
+
+ bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+ clone_slice_in_subprog(&ptr, &data);
+ bpf_ringbuf_submit_dynptr(&ptr, 0);
+ if (data)
+ /* this should fail */
+ *data = 123;
+
+ return 0;
+}
+
/* Invalidating a dynptr should invalidate any data slices
* of its parent
*/
|
| 27/3 | 2026/09/11 08:56 | llm | kmsan-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 5097 output: 38 thoughts: 114 Thoughts: **KMSAN Fuzzing Session Assessment** Okay, let's take a look at this patch and decide if it's worth throwing KMSAN at. First, I need to understand what's being touched. Ah, it's modifying `kernel/bpf/verifier.c` and also adding some BPF selftests, interesting. That area always makes me a little cautious. Let me dig into `kernel/bpf/verifier.c`, specifically around the functions `destroy_dynptrs_on_func_exit` and `prepare_func_exit`. Those are key spots for potential memory safety issues, so I want to understand the surrounding code. I'll fire up `grepper` (or `read-file`, depending on my mood) and get a detailed view of what's going on there. From this I can see what is being added and or modified in relation to dynamic pointers, which is where KMSAN will give the most value. |
| 28/3 | 2026/09/11 08:56 | tool | grepper |
0mArgs:{
"Expression": "destroy_if_dynptr_stack_slot",
"PathPrefix": "kernel/bpf/verifier.c"
}Results: {
"Output": "kernel/bpf/verifier.c=661=static void mark_dynptr_cb_reg(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-667-\nkernel/bpf/verifier.c:668:static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,\nkernel/bpf/verifier.c-669-\t\t\t\t struct bpf_func_state *state, int spi);\n--\nkernel/bpf/verifier.c=671=static int mark_stack_slots_dynptr(struct bpf_verifier_env *env, struct bpf_reg_state *reg,\n--\nkernel/bpf/verifier.c-683-\t/* We cannot assume both spi and spi - 1 belong to the same dynptr,\nkernel/bpf/verifier.c:684:\t * hence we need to call destroy_if_dynptr_stack_slot twice for both,\nkernel/bpf/verifier.c-685-\t * to ensure that for the following example:\n--\nkernel/bpf/verifier.c-691-\t */\nkernel/bpf/verifier.c:692:\terr = destroy_if_dynptr_stack_slot(env, state, spi);\nkernel/bpf/verifier.c-693-\tif (err)\nkernel/bpf/verifier.c-694-\t\treturn err;\nkernel/bpf/verifier.c:695:\terr = destroy_if_dynptr_stack_slot(env, state, spi - 1);\nkernel/bpf/verifier.c-696-\tif (err)\n--\nkernel/bpf/verifier.c=803=static int destroy_dynptrs_on_func_exit(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-819-\t\t */\nkernel/bpf/verifier.c:820:\t\terr = destroy_if_dynptr_stack_slot(env, callee, i);\nkernel/bpf/verifier.c-821-\t\tif (err)\n--\nkernel/bpf/verifier.c-827-\nkernel/bpf/verifier.c:828:static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,\nkernel/bpf/verifier.c-829-\t\t\t\t struct bpf_func_state *state, int spi)\n--\nkernel/bpf/verifier.c=870=static bool is_dynptr_reg_valid_uninit(struct bpf_verifier_env *env, struct bpf_reg_state *reg)\n--\nkernel/bpf/verifier.c-888-\t * STACK_DYNPTR slots, see mark_stack_slots_dynptr which calls\nkernel/bpf/verifier.c:889:\t * destroy_if_dynptr_stack_slot to ensure dynptr objects at the slots we are\nkernel/bpf/verifier.c-890-\t * touching are completely destructed before we reinitialize them for a new\nkernel/bpf/verifier.c:891:\t * one. For referenced ones, destroy_if_dynptr_stack_slot returns an error early\nkernel/bpf/verifier.c-892-\t * instead of delaying it until the end where the user will get \"Unreleased\n--\nkernel/bpf/verifier.c=3541=static int check_stack_write_fixed_off(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-3593-\nkernel/bpf/verifier.c:3594:\terr = destroy_if_dynptr_stack_slot(env, state, spi);\nkernel/bpf/verifier.c-3595-\tif (err)\n--\nkernel/bpf/verifier.c=3684=static int check_stack_write_var_off(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-3713-\t\tspi = bpf_get_spi(i);\nkernel/bpf/verifier.c:3714:\t\terr = destroy_if_dynptr_stack_slot(env, state, spi);\nkernel/bpf/verifier.c-3715-\t\tif (err)\n"
} |
| 29/3 | 2026/09/11 08:56 | llm | kmsan-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 6517 output: 36 thoughts: 54 Thoughts: Here's my take on those two functions, as I understand them: **Dissecting BPF Function Exit Handling** Okay, so I'm digging into how the BPF verifier handles function exits – specifically, the cleanup operations. I'm focusing on `prepare_func_exit` and `destroy_dynptrs_on_func_exit`. I'm going to consult `kernel/bpf/verifier.c` to remind myself of the context, focusing on lines 800 and 10400 for a start. From the function names, I infer that `prepare_func_exit` is likely setting the stage for a function's return, maybe updating some state or performing initial cleanup tasks *before* the actual exit. On the other hand, `destroy_dynptrs_on_func_exit` screams about cleaning up dynamically allocated pointers – BPF programs can be sophisticated, and that type of memory management needs to be carefully handled during function returns to avoid leaks or corruption. This probably involves freeing memory associated with dynamic data structures within a BPF function. I suspect `destroy_dynptrs_on_func_exit` is going to be the more complex of the two, especially if the BPF program uses potentially nested or cyclical pointer structures. I'll need to check how the verifier tracks these dynamic pointers and how it validates their cleanup. It’s possible there are checks on the verifier stack during the exit to ensure all resources are deallocated as designed. I wonder if there are any subtle race conditions or uninitialized memory issues these function address. Let's see what the actual code says... |
| 30/3 | 2026/09/11 08:56 | tool | read-file |
0mArgs:{
"File": "kernel/bpf/verifier.c",
"FirstLine": 800,
"LineCount": 55
}Results: {
"Contents": " 800:\t\treturn ref_cnt;\n 801:\t}\n 802:\t\n 803:\tstatic int destroy_dynptrs_on_func_exit(struct bpf_verifier_env *env,\n 804:\t\t\t\t\t\tstruct bpf_func_state *callee)\n 805:\t{\n 806:\t\tint i, err;\n 807:\t\n 808:\t\tfor (i = 0; i \u003c callee-\u003eallocated_stack / BPF_REG_SIZE; i++) {\n 809:\t\t\tstruct bpf_stack_state *slot = \u0026callee-\u003estack[i];\n 810:\t\n 811:\t\t\tif (slot-\u003eslot_type[0] != STACK_DYNPTR ||\n 812:\t\t\t !slot-\u003espilled_ptr.dynptr.first_slot)\n 813:\t\t\t\tcontinue;\n 814:\t\n 815:\t\t\t/*\n 816:\t\t\t * A callee-local dynptr is destroyed when its stack frame goes\n 817:\t\t\t * away. Apply the normal stack-slot teardown so references cannot\n 818:\t\t\t * be lost and slices derived from that dynptr are invalidated.\n 819:\t\t\t */\n 820:\t\t\terr = destroy_if_dynptr_stack_slot(env, callee, i);\n 821:\t\t\tif (err)\n 822:\t\t\t\treturn err;\n 823:\t\t}\n 824:\t\n 825:\t\treturn 0;\n 826:\t}\n 827:\t\n 828:\tstatic int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,\n 829:\t\t\t\t\t struct bpf_func_state *state, int spi)\n 830:\t{\n 831:\t\tint err = 0;\n 832:\t\n 833:\t\t/* We always ensure that STACK_DYNPTR is never set partially,\n 834:\t\t * hence just checking for slot_type[0] is enough. This is\n 835:\t\t * different for STACK_SPILL, where it may be only set for\n 836:\t\t * 1 byte, so code has to use is_spilled_reg.\n 837:\t\t */\n 838:\t\tif (state-\u003estack[spi].slot_type[0] != STACK_DYNPTR)\n 839:\t\t\treturn 0;\n 840:\t\n 841:\t\t/* Reposition spi to first slot */\n 842:\t\tif (!state-\u003estack[spi].spilled_ptr.dynptr.first_slot)\n 843:\t\t\tspi = spi + 1;\n 844:\t\n 845:\t\t/*\n 846:\t\t * A referenced dynptr can be overwritten only if there is at\n 847:\t\t * least one other dynptr sharing the same virtual ref parent,\n 848:\t\t * ensuring the reference can still be properly released.\n 849:\t\t */\n 850:\t\tif (dynptr_type_referenced(state-\u003estack[spi].spilled_ptr.dynptr.type) \u0026\u0026\n 851:\t\t dynptr_ref_cnt(env, state-\u003estack[spi].spilled_ptr.parent_id) \u003c= 1) {\n 852:\t\t\tverbose(env, \"cannot overwrite referenced dynptr\\n\");\n 853:\t\t\tbpf_diag_res(\n 854:\t\t\t\tenv, env-\u003einsn_idx, \"referenced dynptr overwrite\",\n"
} |
| 31/3 | 2026/09/11 08:56 | llm | kmsan-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 7855 output: 36 thoughts: 19 Thoughts: Okay, here's my interpretation of that thought process, assuming I'm deep in the weeds of some code, probably related to memory management or dynamic pointers, and I'm quite familiar with the function `destroy_if_dynptr_stack_slot`: **Let's Dig into `destroy_if_dynptr_stack_slot`** Alright, so I'm looking at this particular piece of the puzzle... I'm pretty sure I know what `destroy_if_dynptr_stack_slot` *should* be doing, based on the naming convention and where it's probably being used. It's almost certainly related to cleaning up, deallocating, or at least resetting some dynamically allocated memory, likely pointers residing on the stack. I need to refresh myself on the details, though, to ensure I'm remembering the specifics correctly. I've got a mental model of how this whole system works – the interactions between the stack, heap, these dynamic pointers – but I need to make sure this `destroy_if_dynptr_stack_slot` function is behaving as expected, and that it's correctly integrated into the broader resource management. Let's get the full context to see how it is supposed to be working. |
| 32/3 | 2026/09/11 08:56 | tool | read-file |
0mArgs:{
"File": "kernel/bpf/verifier.c",
"FirstLine": 855,
"LineCount": 40
}Results: {
"Contents": " 855:\t\t\t\t\"This stack slot contains a dynptr that owns or protects a referenced resource. Overwriting the last dynptr for that resource would lose the verifier-tracked release path.\",\n 856:\t\t\t\t\"Release or clone the dynptr so another live dynptr still tracks the referenced resource before overwriting this stack slot.\");\n 857:\t\t\treturn -EINVAL;\n 858:\t\t}\n 859:\t\n 860:\t\t/* Invalidate the dynptr and any derived slices */\n 861:\t\terr = release_reference(env, state-\u003estack[spi].spilled_ptr.id);\n 862:\t\tif (!err) {\n 863:\t\t\tmark_stack_slot_scratched(env, spi);\n 864:\t\t\tmark_stack_slot_scratched(env, spi - 1);\n 865:\t\t}\n 866:\t\n 867:\t\treturn err;\n 868:\t}\n 869:\t\n 870:\tstatic bool is_dynptr_reg_valid_uninit(struct bpf_verifier_env *env, struct bpf_reg_state *reg)\n 871:\t{\n 872:\t\tint spi;\n 873:\t\n 874:\t\tif (reg-\u003etype == CONST_PTR_TO_DYNPTR)\n 875:\t\t\treturn false;\n 876:\t\n 877:\t\tspi = dynptr_get_spi(env, reg);\n 878:\t\n 879:\t\t/* -ERANGE (i.e. spi not falling into allocated stack slots) isn't an\n 880:\t\t * error because this just means the stack state hasn't been updated yet.\n 881:\t\t * We will do check_mem_access to check and update stack bounds later.\n 882:\t\t */\n 883:\t\tif (spi \u003c 0 \u0026\u0026 spi != -ERANGE)\n 884:\t\t\treturn false;\n 885:\t\n 886:\t\t/* We don't need to check if the stack slots are marked by previous\n 887:\t\t * dynptr initializations because we allow overwriting existing unreferenced\n 888:\t\t * STACK_DYNPTR slots, see mark_stack_slots_dynptr which calls\n 889:\t\t * destroy_if_dynptr_stack_slot to ensure dynptr objects at the slots we are\n 890:\t\t * touching are completely destructed before we reinitialize them for a new\n 891:\t\t * one. For referenced ones, destroy_if_dynptr_stack_slot returns an error early\n 892:\t\t * instead of delaying it until the end where the user will get \"Unreleased\n 893:\t\t * reference\" error.\n 894:\t\t */\n"
} |
| 33/3 | 2026/09/11 08:56 | llm | kmsan-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 8872 output: 38 thoughts: 20 Thoughts: Here's my summary, as if I were thinking these thoughts: **Analyzing `prepare_func_exit` in Context** Alright, I need to zoom in on `prepare_func_exit`. Let's zero in on around line 10424. That should put me right in the heart of what's going on. I'm guessing this function is critical for proper cleanup during function exits, particularly in the case of something like a stack unwinding, resource deallocation, or exception handling. Depending on the architecture and the language this is probably related to stack frame management. I'll need to look at what's being passed in and exactly what it's doing with these arguments in this specific context to understand its role. I'm expecting to see calls to release any allocated resources or to update the control flow, perhaps using a jump table or something similar, and there might be interactions with a debugger or profiler here as well. I hope the code is well-commented around this section! |
| 34/3 | 2026/09/11 08:56 | tool | read-file |
0mArgs:{
"File": "kernel/bpf/verifier.c",
"FirstLine": 10410,
"LineCount": 40
}Results: {
"Contents": "10410:\t\t/* for callbacks like bpf_loop or bpf_for_each_map_elem go back to callsite,\n10411:\t\t * there function call logic would reschedule callback visit. If iteration\n10412:\t\t * converges is_state_visited() would prune that visit eventually.\n10413:\t\t */\n10414:\t\tin_callback_fn = callee-\u003ein_callback_fn;\n10415:\t\tif (in_callback_fn)\n10416:\t\t\t*insn_idx = callee-\u003ecallsite;\n10417:\t\telse\n10418:\t\t\t*insn_idx = callee-\u003ecallsite + 1;\n10419:\t\n10420:\t\tif (env-\u003elog.level \u0026 BPF_LOG_LEVEL) {\n10421:\t\t\tverbose(env, \"returning from callee:\\n\");\n10422:\t\t\tprint_verifier_state(env, state, callee-\u003eframeno, true);\n10423:\t\t\tverbose(env, \"to caller at %d:\\n\", *insn_idx);\n10424:\t\t\tprint_verifier_state(env, state, caller-\u003eframeno, true);\n10425:\t\t}\n10426:\t\taccount_processed_insns(env, callee, caller);\n10427:\t\terr = destroy_dynptrs_on_func_exit(env, callee);\n10428:\t\tif (err)\n10429:\t\t\treturn err;\n10430:\t\t/* clear everything in the callee. In case of exceptional exits using\n10431:\t\t * bpf_throw, this will be done by copy_verifier_state for extra frames. */\n10432:\t\tfree_func_state(callee);\n10433:\t\tstate-\u003eframe[state-\u003ecurframe--] = NULL;\n10434:\t\tinvalidate_outgoing_stack_args(env, caller);\n10435:\t\n10436:\t\t/* for callbacks widen imprecise scalars to make programs like below verify:\n10437:\t\t *\n10438:\t\t * struct ctx { int i; }\n10439:\t\t * void cb(int idx, struct ctx *ctx) { ctx-\u003ei++; ... }\n10440:\t\t * ...\n10441:\t\t * struct ctx = { .i = 0; }\n10442:\t\t * bpf_loop(100, cb, \u0026ctx, 0);\n10443:\t\t *\n10444:\t\t * This is similar to what is done in process_iter_next_call() for open\n10445:\t\t * coded iterators.\n10446:\t\t */\n10447:\t\tprev_st = in_callback_fn ? find_prev_entry(env, state, *insn_idx) : NULL;\n10448:\t\tif (prev_st) {\n10449:\t\t\terr = widen_imprecise_scalars(env, prev_st, state);\n"
} |
| 35/3 | 2026/09/11 08:56 | llm | kmsan-evaluator |
0mModel:gemini-3.7-flash Args: null Results: null Tokens: input: 9928 output: 319 thoughts: 936 Thoughts: **KMSAN Risk Assessment: BPF Verifier Dynptr Cleanup** Okay, let's break this down. My immediate concern is whether this patch, dealing with BPF verifier dynptr cleanup, introduces any uninitialized memory risks. I need to think this through carefully, considering the potential for KMSAN issues. First, the patch's core function, `destroy_dynptrs_on_func_exit`, focuses on cleaning up dynptrs on a callee's stack frame within the BPF verifier. It iterates through the stack, checks for `STACK_DYNPTR` slots, and releases the references. It's all happening *within* the verifier's static analysis, not during runtime execution of a BPF program. So the question is: can this introduce kernel-to-user information leaks or uninitialized memory reads that would be caught by KMSAN? The KMSAN criteria are fresh in my mind: kernel data to userspace, conditional logic on uninitialized data, uninitialized field reads, and bounds issues leading to uninitialized byte access. Looking closely at the code, `i` and `err` are local, properly initialized integers. `i` is used to index through the stack, and the code only reads initialized fields (`slot_type[0]`, `spilled_ptr.dynptr.first_slot`). There are no kernel-to-user copies, and no kernel memory allocations are uninitialized. This is static analysis at verification time, not run time execution. It is all bounded by `callee->allocated_stack`. The `callee->stack` is allocated and initialized during verifier state creation; the `slot_type` is also initialized. No uninitialized data is read. The primary goal here is to prevent use-after-free or dangling slice accesses in verified BPF programs, which are runtime safety bugs caught by verifier or KASAN, not KMSAN. Therefore, the patch doesn't create any KMSAN concerns. It's about tightening verification, not runtime memory corruption or leaking information. Standard bug detectors (or standard KASAN verifier tests) are appropriate. I'm confident about this. To cement the reasoning, I'll emphasize the distinction between KMSAN and KASAN. KMSAN is for catching uninitialized reads and leaks; KASAN is for the classic memory safety issues. The code added, `destroy_dynptrs_on_func_exit()` in `kernel/bpf/verifier.c` within `prepare_func_exit()`, only touches BPF verifier static analysis, cleaning up dynptrs. The verifier code variables are initialized and bounded, and no kernel data is exposed. Thus, I stand by my 'NeedsKMSAN = false' assessment. |
| 36/3 | 2026/09/11 08:56 | tool | set-results |
0mArgs:{
"KMSANReasoning": "The patch modifies the BPF verifier in `kernel/bpf/verifier.c` by adding `destroy_dynptrs_on_func_exit()`, which is called during `prepare_func_exit()` to ensure that dynptrs allocated on a callee's stack frame are properly destructed and their derived slices invalidated when the subprogram returns.\n\nKMSAN vs KASAN applicability:\n- KMSAN detects reads of uninitialized memory (stack, heap, or page allocations) and uninitialized data leaks to user space.\n- KASAN and standard sanitizers detect memory safety violations such as use-after-free, out-of-bounds accesses, and logic bugs in kernel/verifier verification.\n\nThe changes in this patch:\n1. Operate purely within the BPF verifier's compile-time static analysis state machine (`bpf_func_state`).\n2. All local variables (`i`, `err`) and state accesses (`callee-\u003estack[i]`) are strictly initialized and bounded by `callee-\u003eallocated_stack / BPF_REG_SIZE`.\n3. Do not allocate or expose uninitialized memory, modify copy_to_user paths, or introduce conditional branches on uninitialized fields.\n\nBecause no uninitialized memory risks or kernel-to-user info-leaks are introduced or exposed, a dedicated KMSAN fuzzing session is not warranted.",
"NeedsKMSAN": false
}Results: {
"KMSANReasoning": "The patch modifies the BPF verifier in `kernel/bpf/verifier.c` by adding `destroy_dynptrs_on_func_exit()`, which is called during `prepare_func_exit()` to ensure that dynptrs allocated on a callee's stack frame are properly destructed and their derived slices invalidated when the subprogram returns.\n\nKMSAN vs KASAN applicability:\n- KMSAN detects reads of uninitialized memory (stack, heap, or page allocations) and uninitialized data leaks to user space.\n- KASAN and standard sanitizers detect memory safety violations such as use-after-free, out-of-bounds accesses, and logic bugs in kernel/verifier verification.\n\nThe changes in this patch:\n1. Operate purely within the BPF verifier's compile-time static analysis state machine (`bpf_func_state`).\n2. All local variables (`i`, `err`) and state accesses (`callee-\u003estack[i]`) are strictly initialized and bounded by `callee-\u003eallocated_stack / BPF_REG_SIZE`.\n3. Do not allocate or expose uninitialized memory, modify copy_to_user paths, or introduce conditional branches on uninitialized fields.\n\nBecause no uninitialized memory risks or kernel-to-user info-leaks are introduced or exposed, a dedicated KMSAN fuzzing session is not warranted.",
"NeedsKMSAN": false
} |
| Total Calls | Total Tokens | Avg Tokens | Total Duration (Seconds) | Avg Duration (Seconds) |
|---|
| Total Calls | Total Duration (Seconds) | Avg Duration (Seconds) |
|---|