AI Trajectory

null

{
  "EnableConfigs": [
    "BINFMT_MISC"
  ],
  "FocusSymbols": [
    "load_misc_binary",
    "bm_entry_write",
    "bm_status_write",
    "bm_evict_inode",
    "add_entry",
    "get_binfmt_handler",
    "search_binfmt_handler",
    "remove_binfmt_handler"
  ],
  "Reasoning": "The patch changes the internal data structures of `binfmt_misc` from a doubly-linked list with a rwlock to an RCU-protected hash list with a spinlock. This is a functional change affecting the core logic of `binfmt_misc` registration, unregistration, and binary execution. It is worth fuzzing to ensure the new RCU logic and lockless traversal do not introduce race conditions, use-after-free, or other memory safety issues.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit a29175787377a783bf29eecfe42f43a53dc77afd\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Thu Jul 9 10:32:25 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c\nindex 84349fcb93f13a..0f04709a0a39f5 100644\n--- a/fs/binfmt_misc.c\n+++ b/fs/binfmt_misc.c\n@@ -24,6 +24,7 @@\n #include \u003clinux/pagemap.h\u003e\n #include \u003clinux/namei.h\u003e\n #include \u003clinux/mount.h\u003e\n+#include \u003clinux/rculist.h\u003e\n #include \u003clinux/fs_context.h\u003e\n #include \u003clinux/syscalls.h\u003e\n #include \u003clinux/fs.h\u003e\n@@ -48,7 +49,7 @@ enum {Enabled, Magic};\n #define MISC_FMT_OPEN_FILE (1UL \u003c\u003c 28)\n \n typedef struct {\n-\tstruct list_head list;\n+\tstruct hlist_node node;\n \tunsigned long flags;\t\t/* type, status, etc. */\n \tint offset;\t\t\t/* offset of magic */\n \tint size;\t\t\t/* size of magic/mask */\n@@ -59,6 +60,7 @@ typedef struct {\n \tstruct dentry *dentry;\n \tstruct file *interp_file;\n \trefcount_t users;\t\t/* sync removal with load_misc_binary() */\n+\tstruct rcu_head rcu;\n } Node;\n \n static struct file_system_type bm_fs_type;\n@@ -86,6 +88,8 @@ static struct file_system_type bm_fs_type;\n  * Search for a binary type handler for @bprm in the list of registered binary\n  * type handlers.\n  *\n+ * The caller must hold the RCU read lock.\n+ *\n  * Return: binary type list entry on success, NULL on failure\n  */\n static Node *search_binfmt_handler(struct binfmt_misc *misc,\n@@ -95,7 +99,7 @@ static Node *search_binfmt_handler(struct binfmt_misc *misc,\n \tNode *e;\n \n \t/* Walk all the registered handlers. */\n-\tlist_for_each_entry(e, \u0026misc-\u003eentries, list) {\n+\thlist_for_each_entry_rcu(e, \u0026misc-\u003eentries, node) {\n \t\tchar *s;\n \t\tint j;\n \n@@ -134,7 +138,10 @@ static Node *search_binfmt_handler(struct binfmt_misc *misc,\n  * @bprm: binary for which we are looking for a handler\n  *\n  * Try to find a binfmt handler for the binary type. If one is found take a\n- * reference to protect against removal via bm_{entry,status}_write().\n+ * reference to protect against removal via bm_{entry,status}_write(). The\n+ * refcount of an entry can only drop to zero once it has been unlinked and\n+ * a restarted search cannot find an unlinked entry again so the retry loop\n+ * is bounded.\n  *\n  * Return: binary type list entry on success, NULL on failure\n  */\n@@ -143,11 +150,10 @@ static Node *get_binfmt_handler(struct binfmt_misc *misc,\n {\n \tNode *e;\n \n-\tread_lock(\u0026misc-\u003eentries_lock);\n-\te = search_binfmt_handler(misc, bprm);\n-\tif (e)\n-\t\trefcount_inc(\u0026e-\u003eusers);\n-\tread_unlock(\u0026misc-\u003eentries_lock);\n+\tguard(rcu)();\n+\tdo {\n+\t\te = search_binfmt_handler(misc, bprm);\n+\t} while (e \u0026\u0026 !refcount_inc_not_zero(\u0026e-\u003eusers));\n \treturn e;\n }\n \n@@ -164,7 +170,8 @@ static void put_binfmt_handler(Node *e)\n \tif (refcount_dec_and_test(\u0026e-\u003eusers)) {\n \t\tif (e-\u003eflags \u0026 MISC_FMT_OPEN_FILE)\n \t\t\tfilp_close(e-\u003einterp_file, NULL);\n-\t\tkfree(e);\n+\t\t/* Lockless walkers may still dereference this entry. */\n+\t\tkfree_rcu(e, rcu);\n \t}\n }\n \n@@ -208,7 +215,7 @@ static int load_misc_binary(struct linux_binprm *bprm)\n \tstruct binfmt_misc *misc;\n \n \tmisc = load_binfmt_misc();\n-\tif (!misc-\u003eenabled)\n+\tif (!READ_ONCE(misc-\u003eenabled))\n \t\treturn retval;\n \n \tfmt = get_binfmt_handler(misc, bprm);\n@@ -654,8 +661,8 @@ static struct binfmt_misc *i_binfmt_misc(struct inode *inode)\n  *\n  * If the -\u003eevict call was not caused by a super block shutdown but by a write\n  * to remove the entry or all entries via bm_{entry,status}_write() the entry\n- * will have already been removed from the list. We keep the list_empty() check\n- * to make that explicit.\n+ * will have already been removed from the list. We keep the hlist_unhashed()\n+ * check to make that explicit.\n */\n static void bm_evict_inode(struct inode *inode)\n {\n@@ -667,10 +674,10 @@ static void bm_evict_inode(struct inode *inode)\n \t\tstruct binfmt_misc *misc;\n \n \t\tmisc = i_binfmt_misc(inode);\n-\t\twrite_lock(\u0026misc-\u003eentries_lock);\n-\t\tif (!list_empty(\u0026e-\u003elist))\n-\t\t\tlist_del_init(\u0026e-\u003elist);\n-\t\twrite_unlock(\u0026misc-\u003eentries_lock);\n+\t\tspin_lock(\u0026misc-\u003eentries_lock);\n+\t\tif (!hlist_unhashed(\u0026e-\u003enode))\n+\t\t\thlist_del_init_rcu(\u0026e-\u003enode);\n+\t\tspin_unlock(\u0026misc-\u003eentries_lock);\n \t\tput_binfmt_handler(e);\n \t}\n }\n@@ -689,9 +696,9 @@ static void bm_evict_inode(struct inode *inode)\n  */\n static void remove_binfmt_handler(struct binfmt_misc *misc, Node *e)\n {\n-\twrite_lock(\u0026misc-\u003eentries_lock);\n-\tlist_del_init(\u0026e-\u003elist);\n-\twrite_unlock(\u0026misc-\u003eentries_lock);\n+\tspin_lock(\u0026misc-\u003eentries_lock);\n+\thlist_del_init_rcu(\u0026e-\u003enode);\n+\tspin_unlock(\u0026misc-\u003eentries_lock);\n \tlocked_recursive_removal(e-\u003edentry, NULL);\n }\n \n@@ -742,11 +749,13 @@ static ssize_t bm_entry_write(struct file *file, const char __user *buffer,\n \t\t * via bm_{entry,register,status}_write() inode_lock() on the\n \t\t * root inode must be held.\n \t\t * The lock is exclusive ensuring that the list can't be\n-\t\t * modified. Only load_misc_binary() can access but does so\n-\t\t * read-only. So we only need to take the write lock when we\n-\t\t * actually remove the entry from the list.\n+\t\t * modified. Only load_misc_binary() can access the list\n+\t\t * concurrently and it does so under RCU. So entries_lock only\n+\t\t * needs to be held when an entry is actually unlinked to\n+\t\t * serialize against bm_evict_inode() during umount which\n+\t\t * unlinks without holding inode_lock.\n \t\t */\n-\t\tif (!list_empty(\u0026e-\u003elist))\n+\t\tif (!hlist_unhashed(\u0026e-\u003enode))\n \t\t\tremove_binfmt_handler(i_binfmt_misc(inode), e);\n \n \t\tinode_unlock(inode);\n@@ -789,9 +798,9 @@ static int add_entry(Node *e, struct super_block *sb)\n \n \td_make_persistent(dentry, inode);\n \tmisc = i_binfmt_misc(inode);\n-\twrite_lock(\u0026misc-\u003eentries_lock);\n-\tlist_add(\u0026e-\u003elist, \u0026misc-\u003eentries);\n-\twrite_unlock(\u0026misc-\u003eentries_lock);\n+\tspin_lock(\u0026misc-\u003eentries_lock);\n+\thlist_add_head_rcu(\u0026e-\u003enode, \u0026misc-\u003eentries);\n+\tspin_unlock(\u0026misc-\u003eentries_lock);\n \tsimple_done_creating(dentry);\n \treturn 0;\n }\n@@ -854,7 +863,7 @@ bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)\n \tchar *s;\n \n \tmisc = i_binfmt_misc(file_inode(file));\n-\ts = misc-\u003eenabled ? \"enabled\\n\" : \"disabled\\n\";\n+\ts = READ_ONCE(misc-\u003eenabled) ? \"enabled\\n\" : \"disabled\\n\";\n \treturn simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));\n }\n \n@@ -863,18 +872,19 @@ static ssize_t bm_status_write(struct file *file, const char __user *buffer,\n {\n \tstruct binfmt_misc *misc;\n \tint res = parse_command(buffer, count);\n-\tNode *e, *next;\n+\tstruct hlist_node *next;\n \tstruct inode *inode;\n+\tNode *e;\n \n \tmisc = i_binfmt_misc(file_inode(file));\n \tswitch (res) {\n \tcase 1:\n \t\t/* Disable all handlers. */\n-\t\tmisc-\u003eenabled = false;\n+\t\tWRITE_ONCE(misc-\u003eenabled, false);\n \t\tbreak;\n \tcase 2:\n \t\t/* Enable all handlers. */\n-\t\tmisc-\u003eenabled = true;\n+\t\tWRITE_ONCE(misc-\u003eenabled, true);\n \t\tbreak;\n \tcase 3:\n \t\t/* Delete all handlers. */\n@@ -886,11 +896,13 @@ static ssize_t bm_status_write(struct file *file, const char __user *buffer,\n \t\t * via bm_{entry,register,status}_write() inode_lock() on the\n \t\t * root inode must be held.\n \t\t * The lock is exclusive ensuring that the list can't be\n-\t\t * modified. Only load_misc_binary() can access but does so\n-\t\t * read-only. So we only need to take the write lock when we\n-\t\t * actually remove the entry from the list.\n+\t\t * modified. Only load_misc_binary() can access the list\n+\t\t * concurrently and it does so under RCU. So entries_lock only\n+\t\t * needs to be held when an entry is actually unlinked to\n+\t\t * serialize against bm_evict_inode() during umount which\n+\t\t * unlinks without holding inode_lock.\n \t\t */\n-\t\tlist_for_each_entry_safe(e, next, \u0026misc-\u003eentries, list)\n+\t\thlist_for_each_entry_safe(e, next, \u0026misc-\u003eentries, node)\n \t\t\tremove_binfmt_handler(misc, e);\n \n \t\tinode_unlock(inode);\n@@ -965,8 +977,8 @@ static int bm_fill_super(struct super_block *sb, struct fs_context *fc)\n \t\tif (!misc)\n \t\t\treturn -ENOMEM;\n \n-\t\tINIT_LIST_HEAD(\u0026misc-\u003eentries);\n-\t\trwlock_init(\u0026misc-\u003eentries_lock);\n+\t\tINIT_HLIST_HEAD(\u0026misc-\u003eentries);\n+\t\tspin_lock_init(\u0026misc-\u003eentries_lock);\n \n \t\t/* Pairs with smp_load_acquire() in load_binfmt_misc(). */\n \t\tsmp_store_release(\u0026user_ns-\u003ebinfmt_misc, misc);\n@@ -983,7 +995,7 @@ static int bm_fill_super(struct super_block *sb, struct fs_context *fc)\n \t * someone mounts binfmt_misc for the first time or again we simply\n \t * reset -\u003eenabled to true.\n \t */\n-\tmisc-\u003eenabled = true;\n+\tWRITE_ONCE(misc-\u003eenabled, true);\n \n \terr = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);\n \tif (!err)\ndiff --git a/include/linux/binfmts.h b/include/linux/binfmts.h\nindex 2c77e383e73757..7e7333b7bb0f11 100644\n--- a/include/linux/binfmts.h\n+++ b/include/linux/binfmts.h\n@@ -101,8 +101,8 @@ struct linux_binfmt {\n \n #if IS_ENABLED(CONFIG_BINFMT_MISC)\n struct binfmt_misc {\n-\tstruct list_head entries;\n-\trwlock_t entries_lock;\n+\tstruct hlist_head entries;\n+\tspinlock_t entries_lock;\n \tbool enabled;\n } __randomize_layout;\n \ndiff --git a/kernel/user.c b/kernel/user.c\nindex 7aef4e679a6a0c..21bafdc1137956 100644\n--- a/kernel/user.c\n+++ b/kernel/user.c\n@@ -23,9 +23,9 @@\n \n #if IS_ENABLED(CONFIG_BINFMT_MISC)\n struct binfmt_misc init_binfmt_misc = {\n-\t.entries = LIST_HEAD_INIT(init_binfmt_misc.entries),\n+\t.entries = HLIST_HEAD_INIT,\n \t.enabled = true,\n-\t.entries_lock = __RW_LOCK_UNLOCKED(init_binfmt_misc.entries_lock),\n+\t.entries_lock = __SPIN_LOCK_UNLOCKED(init_binfmt_misc.entries_lock),\n };\n EXPORT_SYMBOL_GPL(init_binfmt_misc);\n #endif\n"
}

gemini-3.1-pro-preview

null

{
  "EnableConfigs": [
    "BINFMT_MISC"
  ],
  "FocusSymbols": [
    "load_misc_binary",
    "bm_entry_write",
    "bm_status_write",
    "bm_evict_inode",
    "add_entry",
    "get_binfmt_handler",
    "search_binfmt_handler",
    "remove_binfmt_handler"
  ],
  "Reasoning": "The patch changes the internal data structures of `binfmt_misc` from a doubly-linked list with a rwlock to an RCU-protected hash list with a spinlock. This is a functional change affecting the core logic of `binfmt_misc` registration, unregistration, and binary execution. It is worth fuzzing to ensure the new RCU logic and lockless traversal do not introduce race conditions, use-after-free, or other memory safety issues.",
  "WorthFuzzing": true
}

You are an expert Linux kernel maintainer.
Your job is to review a provided patch series and determine
if it makes functional changes to the kernel that should be fuzzed.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on your internal knowledge of the kernel. You must actively
use your code access tools to examine the actual source code and confirm any assumptions.

Return WorthFuzzing=false if the patch only contains:
- Modifications to Documentation/, Kconfig files, or code comments.
- Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints.
- Changes to numeric constants or macros that do not functionally alter execution flow.
- Code paths that are impossible to reach in virtualized environments like GCE or QEMU,
even when utilizing software-emulated hardware (e.g., usb gadget, mac80211_hwsim).

If it modifies reachable core kernel logic, drivers, or architectures, use your code search
tools to verify the code can be executed, then return WorthFuzzing=true.

When returning WorthFuzzing=true, you MUST ALSO:
1. Extract any specific kernel functions that should be heavily fuzzed into FocusSymbols.
   Avoid listing generic hot-path functions to prevent skewed test distributions.
2. Identify any specific CONFIG_ options required to properly test this new/modified feature.
   Go and look into the Kconfig files and check for ifdefs around the code, do not make assumptions.
   Do not list too generic configs (we already have them enabled). Only list those that
   specifically cover the modified code. List them in the EnableConfigs output array,
   and DO NOT add a '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.

For your convenience, here is the diff of the changes:
commit a29175787377a783bf29eecfe42f43a53dc77afd
Author: syz-cluster <triage@syzkaller.com>
Date:   Thu Jul 9 10:32:25 2026 +0000

    syz-cluster: applied patch under review

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 84349fcb93f13a..0f04709a0a39f5 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -24,6 +24,7 @@
 #include <linux/pagemap.h>
 #include <linux/namei.h>
 #include <linux/mount.h>
+#include <linux/rculist.h>
 #include <linux/fs_context.h>
 #include <linux/syscalls.h>
 #include <linux/fs.h>
@@ -48,7 +49,7 @@ enum {Enabled, Magic};
 #define MISC_FMT_OPEN_FILE (1UL << 28)
 
 typedef struct {
-	struct list_head list;
+	struct hlist_node node;
 	unsigned long flags;		/* type, status, etc. */
 	int offset;			/* offset of magic */
 	int size;			/* size of magic/mask */
@@ -59,6 +60,7 @@ typedef struct {
 	struct dentry *dentry;
 	struct file *interp_file;
 	refcount_t users;		/* sync removal with load_misc_binary() */
+	struct rcu_head rcu;
 } Node;
 
 static struct file_system_type bm_fs_type;
@@ -86,6 +88,8 @@ static struct file_system_type bm_fs_type;
  * Search for a binary type handler for @bprm in the list of registered binary
  * type handlers.
  *
+ * The caller must hold the RCU read lock.
+ *
  * Return: binary type list entry on success, NULL on failure
  */
 static Node *search_binfmt_handler(struct binfmt_misc *misc,
@@ -95,7 +99,7 @@ static Node *search_binfmt_handler(struct binfmt_misc *misc,
 	Node *e;
 
 	/* Walk all the registered handlers. */
-	list_for_each_entry(e, &misc->entries, list) {
+	hlist_for_each_entry_rcu(e, &misc->entries, node) {
 		char *s;
 		int j;
 
@@ -134,7 +138,10 @@ static Node *search_binfmt_handler(struct binfmt_misc *misc,
  * @bprm: binary for which we are looking for a handler
  *
  * Try to find a binfmt handler for the binary type. If one is found take a
- * reference to protect against removal via bm_{entry,status}_write().
+ * reference to protect against removal via bm_{entry,status}_write(). The
+ * refcount of an entry can only drop to zero once it has been unlinked and
+ * a restarted search cannot find an unlinked entry again so the retry loop
+ * is bounded.
  *
  * Return: binary type list entry on success, NULL on failure
  */
@@ -143,11 +150,10 @@ static Node *get_binfmt_handler(struct binfmt_misc *misc,
 {
 	Node *e;
 
-	read_lock(&misc->entries_lock);
-	e = search_binfmt_handler(misc, bprm);
-	if (e)
-		refcount_inc(&e->users);
-	read_unlock(&misc->entries_lock);
+	guard(rcu)();
+	do {
+		e = search_binfmt_handler(misc, bprm);
+	} while (e && !refcount_inc_not_zero(&e->users));
 	return e;
 }
 
@@ -164,7 +170,8 @@ static void put_binfmt_handler(Node *e)
 	if (refcount_dec_and_test(&e->users)) {
 		if (e->flags & MISC_FMT_OPEN_FILE)
 			filp_close(e->interp_file, NULL);
-		kfree(e);
+		/* Lockless walkers may still dereference this entry. */
+		kfree_rcu(e, rcu);
 	}
 }
 
@@ -208,7 +215,7 @@ static int load_misc_binary(struct linux_binprm *bprm)
 	struct binfmt_misc *misc;
 
 	misc = load_binfmt_misc();
-	if (!misc->enabled)
+	if (!READ_ONCE(misc->enabled))
 		return retval;
 
 	fmt = get_binfmt_handler(misc, bprm);
@@ -654,8 +661,8 @@ static struct binfmt_misc *i_binfmt_misc(struct inode *inode)
  *
  * If the ->evict call was not caused by a super block shutdown but by a write
  * to remove the entry or all entries via bm_{entry,status}_write() the entry
- * will have already been removed from the list. We keep the list_empty() check
- * to make that explicit.
+ * will have already been removed from the list. We keep the hlist_unhashed()
+ * check to make that explicit.
 */
 static void bm_evict_inode(struct inode *inode)
 {
@@ -667,10 +674,10 @@ static void bm_evict_inode(struct inode *inode)
 		struct binfmt_misc *misc;
 
 		misc = i_binfmt_misc(inode);
-		write_lock(&misc->entries_lock);
-		if (!list_empty(&e->list))
-			list_del_init(&e->list);
-		write_unlock(&misc->entries_lock);
+		spin_lock(&misc->entries_lock);
+		if (!hlist_unhashed(&e->node))
+			hlist_del_init_rcu(&e->node);
+		spin_unlock(&misc->entries_lock);
 		put_binfmt_handler(e);
 	}
 }
@@ -689,9 +696,9 @@ static void bm_evict_inode(struct inode *inode)
  */
 static void remove_binfmt_handler(struct binfmt_misc *misc, Node *e)
 {
-	write_lock(&misc->entries_lock);
-	list_del_init(&e->list);
-	write_unlock(&misc->entries_lock);
+	spin_lock(&misc->entries_lock);
+	hlist_del_init_rcu(&e->node);
+	spin_unlock(&misc->entries_lock);
 	locked_recursive_removal(e->dentry, NULL);
 }
 
@@ -742,11 +749,13 @@ static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 		 * via bm_{entry,register,status}_write() inode_lock() on the
 		 * root inode must be held.
 		 * The lock is exclusive ensuring that the list can't be
-		 * modified. Only load_misc_binary() can access but does so
-		 * read-only. So we only need to take the write lock when we
-		 * actually remove the entry from the list.
+		 * modified. Only load_misc_binary() can access the list
+		 * concurrently and it does so under RCU. So entries_lock only
+		 * needs to be held when an entry is actually unlinked to
+		 * serialize against bm_evict_inode() during umount which
+		 * unlinks without holding inode_lock.
 		 */
-		if (!list_empty(&e->list))
+		if (!hlist_unhashed(&e->node))
 			remove_binfmt_handler(i_binfmt_misc(inode), e);
 
 		inode_unlock(inode);
@@ -789,9 +798,9 @@ static int add_entry(Node *e, struct super_block *sb)
 
 	d_make_persistent(dentry, inode);
 	misc = i_binfmt_misc(inode);
-	write_lock(&misc->entries_lock);
-	list_add(&e->list, &misc->entries);
-	write_unlock(&misc->entries_lock);
+	spin_lock(&misc->entries_lock);
+	hlist_add_head_rcu(&e->node, &misc->entries);
+	spin_unlock(&misc->entries_lock);
 	simple_done_creating(dentry);
 	return 0;
 }
@@ -854,7 +863,7 @@ bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 	char *s;
 
 	misc = i_binfmt_misc(file_inode(file));
-	s = misc->enabled ? "enabled\n" : "disabled\n";
+	s = READ_ONCE(misc->enabled) ? "enabled\n" : "disabled\n";
 	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 }
 
@@ -863,18 +872,19 @@ static ssize_t bm_status_write(struct file *file, const char __user *buffer,
 {
 	struct binfmt_misc *misc;
 	int res = parse_command(buffer, count);
-	Node *e, *next;
+	struct hlist_node *next;
 	struct inode *inode;
+	Node *e;
 
 	misc = i_binfmt_misc(file_inode(file));
 	switch (res) {
 	case 1:
 		/* Disable all handlers. */
-		misc->enabled = false;
+		WRITE_ONCE(misc->enabled, false);
 		break;
 	case 2:
 		/* Enable all handlers. */
-		misc->enabled = true;
+		WRITE_ONCE(misc->enabled, true);
 		break;
 	case 3:
 		/* Delete all handlers. */
@@ -886,11 +896,13 @@ static ssize_t bm_status_write(struct file *file, const char __user *buffer,
 		 * via bm_{entry,register,status}_write() inode_lock() on the
 		 * root inode must be held.
 		 * The lock is exclusive ensuring that the list can't be
-		 * modified. Only load_misc_binary() can access but does so
-		 * read-only. So we only need to take the write lock when we
-		 * actually remove the entry from the list.
+		 * modified. Only load_misc_binary() can access the list
+		 * concurrently and it does so under RCU. So entries_lock only
+		 * needs to be held when an entry is actually unlinked to
+		 * serialize against bm_evict_inode() during umount which
+		 * unlinks without holding inode_lock.
 		 */
-		list_for_each_entry_safe(e, next, &misc->entries, list)
+		hlist_for_each_entry_safe(e, next, &misc->entries, node)
 			remove_binfmt_handler(misc, e);
 
 		inode_unlock(inode);
@@ -965,8 +977,8 @@ static int bm_fill_super(struct super_block *sb, struct fs_context *fc)
 		if (!misc)
 			return -ENOMEM;
 
-		INIT_LIST_HEAD(&misc->entries);
-		rwlock_init(&misc->entries_lock);
+		INIT_HLIST_HEAD(&misc->entries);
+		spin_lock_init(&misc->entries_lock);
 
 		/* Pairs with smp_load_acquire() in load_binfmt_misc(). */
 		smp_store_release(&user_ns->binfmt_misc, misc);
@@ -983,7 +995,7 @@ static int bm_fill_super(struct super_block *sb, struct fs_context *fc)
 	 * someone mounts binfmt_misc for the first time or again we simply
 	 * reset ->enabled to true.
 	 */
-	misc->enabled = true;
+	WRITE_ONCE(misc->enabled, true);
 
 	err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
 	if (!err)
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 2c77e383e73757..7e7333b7bb0f11 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -101,8 +101,8 @@ struct linux_binfmt {
 
 #if IS_ENABLED(CONFIG_BINFMT_MISC)
 struct binfmt_misc {
-	struct list_head entries;
-	rwlock_t entries_lock;
+	struct hlist_head entries;
+	spinlock_t entries_lock;
 	bool enabled;
 } __randomize_layout;
 
diff --git a/kernel/user.c b/kernel/user.c
index 7aef4e679a6a0c..21bafdc1137956 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -23,9 +23,9 @@
 
 #if IS_ENABLED(CONFIG_BINFMT_MISC)
 struct binfmt_misc init_binfmt_misc = {
-	.entries = LIST_HEAD_INIT(init_binfmt_misc.entries),
+	.entries = HLIST_HEAD_INIT,
 	.enabled = true,
-	.entries_lock = __RW_LOCK_UNLOCKED(init_binfmt_misc.entries_lock),
+	.entries_lock = __SPIN_LOCK_UNLOCKED(init_binfmt_misc.entries_lock),
 };
 EXPORT_SYMBOL_GPL(init_binfmt_misc);
 #endif

gemini-3.1-pro-preview

null

null

							input: 5140
							output: 28
							thoughts: 400
						

**Analyzing the Binfmt_Misc Patch**

Okay, so I'm looking at a patch that's making some fundamental changes to the binfmt_misc subsystem. This is a core kernel area, specifically around how the kernel handles miscellaneous binary formats. The patch touches `fs/binfmt_misc.c`, `include/linux/binfmts.h`, and `kernel/user.c`, which immediately flags this as potentially significant.

The core of the change appears to be a switch from a doubly-linked list (`struct list_head`) to a hash list (`struct hlist_head`) for the `entries` list in `struct binfmt_misc`. We're also seeing a lock upgrade. The patch changes `entries_lock` from a read-write lock (`rwlock_t`) to a spinlock (`spinlock_t`). This suggests a potential performance optimization, though it also increases the risk of contention in certain scenarios. It also seems they're leveraging RCU (Read-Copy-Update) for lockless traversal in `get_binfmt_handler` and `search_binfmt_handler`, which is an interesting design choice. This definitely calls for some careful scrutiny.

My immediate thought is, this is a prime candidate for fuzzing. Any change to core kernel logic warrants a thorough examination for potential vulnerabilities and edge cases. I need to pinpoint the critical functions affected to direct my fuzzing efforts.

Let's see… Based on the diff, the following functions are modified or directly involved: `search_binfmt_handler`, `get_binfmt_handler`, `put_binfmt_handler`, `load_misc_binary`, `bm_evict_inode`, `remove_binfmt_handler`, `bm_entry_write`, `add_entry`, `bm_status_read`, `bm_status_write`, and `bm_fill_super`.

Okay, so `load_misc_binary` is the money shot – it's the main entry point for binary execution through binfmt_misc. `bm_entry_write`, `bm_status_write`, and `bm_status_read` are the user-space interfaces for configuring binfmt_misc. `bm_evict_inode` handles inode eviction, so it's probably less critical from a direct attack surface perspective but still relevant for stability.

Before I go further, I need to confirm the configuration option. The code seems to be guarded by `CONFIG_BINFMT_MISC`. I should quickly verify this by checking `fs/Kconfig.binfmt` or `fs/Makefile` to make sure I understand the build-time dependencies.

{
  "Expression": "BINFMT_MISC",
  "PathPrefix": "fs/"
}

{
  "Output": "fs/Kconfig.binfmt=138=config BINFMT_ZFLAT\n--\nfs/Kconfig.binfmt-144-\nfs/Kconfig.binfmt:145:config BINFMT_MISC\nfs/Kconfig.binfmt-146-\ttristate \"Kernel support for MISC binaries\"\n--\nfs/Makefile=34=obj-$(CONFIG_FILE_LOCKING)      += locks.o\nfs/Makefile:35:obj-$(CONFIG_BINFMT_MISC)\t+= binfmt_misc.o\nfs/Makefile-36-obj-$(CONFIG_BINFMT_SCRIPT)\t+= binfmt_script.o\n--\nfs/file_table.c=165=static int __init init_fs_stat_sysctls(void)\n--\nfs/file_table.c-167-\tregister_sysctl_init(\"fs\", fs_stat_sysctls);\nfs/file_table.c:168:\tif (IS_ENABLED(CONFIG_BINFMT_MISC)) {\nfs/file_table.c-169-\t\tstruct ctl_table_header *hdr;\n"
}

gemini-3.1-pro-preview

null

null

							input: 6427
							output: 66
							thoughts: 32
						

Okay, here's my take on those thoughts, framed as my own:

**Analyzing the BINFMT_MISC Configuration**

Alright, so the key configuration option we're looking at is `BINFMT_MISC`.  That's the starting point. Time to dive into the implementation. My first step is to crack open `fs/binfmt_misc.c`. I need to review the source code for this specific feature in Linux, and identify the core functions that handle this functionality. I'm especially interested in understanding the interactions of the relevant files and functions. I need to be sure I'm across the basics before digging any deeper. Let's see what's in there.

{
  "Expression": "^(static|int|void).* (load_misc_binary|bm_entry_write|bm_status_write|bm_evict_inode|add_entry)\\(",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "Output": "fs/binfmt_misc.c=189=static struct binfmt_misc *load_binfmt_misc(void)\n--\nfs/binfmt_misc.c-209- */\nfs/binfmt_misc.c:210:static int load_misc_binary(struct linux_binprm *bprm)\nfs/binfmt_misc.c-211-{\n--\nfs/binfmt_misc.c=649=static struct binfmt_misc *i_binfmt_misc(struct inode *inode)\n--\nfs/binfmt_misc.c-666-*/\nfs/binfmt_misc.c:667:static void bm_evict_inode(struct inode *inode)\nfs/binfmt_misc.c-668-{\n--\nfs/binfmt_misc.c=708=bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)\n--\nfs/binfmt_misc.c-725-\nfs/binfmt_misc.c:726:static ssize_t bm_entry_write(struct file *file, const char __user *buffer,\nfs/binfmt_misc.c-727-\t\t\t\tsize_t count, loff_t *ppos)\n--\nfs/binfmt_misc.c=770=static const struct file_operations bm_entry_operations = {\n--\nfs/binfmt_misc.c-778-/* add to filesystem */\nfs/binfmt_misc.c:779:static int add_entry(Node *e, struct super_block *sb)\nfs/binfmt_misc.c-780-{\n--\nfs/binfmt_misc.c=860=bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)\n--\nfs/binfmt_misc.c-869-\nfs/binfmt_misc.c:870:static ssize_t bm_status_write(struct file *file, const char __user *buffer,\nfs/binfmt_misc.c-871-\t\tsize_t count, loff_t *ppos)\n"
}

gemini-3.1-pro-preview

null

null

							input: 7223
							output: 33
							thoughts: 176
						

**Analyzing Function Scope in the Kernel Module**

Okay, so I'm looking at these functions: `load_misc_binary`, `bm_evict_inode`, `bm_entry_write`, `add_entry`, and `bm_status_write`. I need to understand their scope within this module. The first thing I'll do is confirm whether these are static or not. A quick check reveals that `add_entry` is static, as is `bm_evict_inode`, and also `bm_entry_write` and also `bm_status_write`, and also `load_misc_binary`.

Wait a minute, `load_misc_binary`... I remember seeing that name somewhere before. It's used in the `linux_binfmt` struct. I think it's registered in the kernel as a binary format handler. Better double-check `fs/binfmt_misc.c`. I need to understand how this function integrates with the wider kernel binary handling process.

{
  "Expression": "struct linux_binfmt",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "Output": "fs/binfmt_misc.c=1022=static int bm_init_fs_context(struct fs_context *fc)\n--\nfs/binfmt_misc.c-1027-\nfs/binfmt_misc.c:1028:static struct linux_binfmt misc_format = {\nfs/binfmt_misc.c-1029-\t.module = THIS_MODULE,\n"
}

gemini-3.1-pro-preview

null

null

							input: 7755
							output: 200
							thoughts: 470
						

**My Analysis of the `binfmt_misc` Patch**

Okay, so I've been looking at this patch and, right off the bat, `load_misc_binary` is clearly the `.load_binary` callback. Makes sense. `bm_entry_write` and `bm_status_write` are the `.write` callbacks for the `binfmt_misc` filesystem, and `bm_evict_inode` is the `.evict_inode` callback. These are all critical entry points, the functions that interact directly with the core logic.

These four, along with `add_entry`, `get_binfmt_handler`, `search_binfmt_handler`, and `remove_binfmt_handler` are definite candidates for `FocusSymbols`. Hold on though, `get_binfmt_handler` and `search_binfmt_handler` also look like they're being *modified* in a significant way, particularly with respect to that RCU logic. Yup, those need to be included.

Before I lock that down, I'll quickly check for any other relevant configurations that might be impacted. The patch touches `fs/binfmt_misc.c`, `include/linux/binfmts.h`, and `kernel/user.c`, which makes `CONFIG_BINFMT_MISC` the obvious primary one.

Now, let's nail down the rationale. This patch fundamentally alters the internal data structures of `binfmt_misc`. It's moving from a doubly-linked list protected by a read-write lock to an RCU-protected hash list with a spinlock. This is a *functional change*; it's altering the registration, unregistration, and execution logic of `binfmt_misc`. That's a huge potential attack surface. We need to fuzz this aggressively to ensure the new RCU logic and lockless traversal don't introduce any nasty race conditions, use-after-frees, or other memory safety issues.

So, here's my `FocusSymbols`:

-   `load_misc_binary`
-   `bm_entry_write`
-   `bm_status_write`
-   `bm_evict_inode`
-   `add_entry`
-   `get_binfmt_handler`
-   `search_binfmt_handler`
-   `remove_binfmt_handler`

And the `EnableConfigs`:

-   `BINFMT_MISC`

I'm ready to call `set-results`.

{
  "EnableConfigs": [
    "BINFMT_MISC"
  ],
  "FocusSymbols": [
    "load_misc_binary",
    "bm_entry_write",
    "bm_status_write",
    "bm_evict_inode",
    "add_entry",
    "get_binfmt_handler",
    "search_binfmt_handler",
    "remove_binfmt_handler"
  ],
  "Reasoning": "The patch changes the internal data structures of `binfmt_misc` from a doubly-linked list with a rwlock to an RCU-protected hash list with a spinlock. This is a functional change affecting the core logic of `binfmt_misc` registration, unregistration, and binary execution. It is worth fuzzing to ensure the new RCU logic and lockless traversal do not introduce race conditions, use-after-free, or other memory safety issues.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "BINFMT_MISC"
  ],
  "FocusSymbols": [
    "load_misc_binary",
    "bm_entry_write",
    "bm_status_write",
    "bm_evict_inode",
    "add_entry",
    "get_binfmt_handler",
    "search_binfmt_handler",
    "remove_binfmt_handler"
  ],
  "Reasoning": "The patch changes the internal data structures of `binfmt_misc` from a doubly-linked list with a rwlock to an RCU-protected hash list with a spinlock. This is a functional change affecting the core logic of `binfmt_misc` registration, unregistration, and binary execution. It is worth fuzzing to ensure the new RCU logic and lockless traversal do not introduce race conditions, use-after-free, or other memory safety issues.",
  "WorthFuzzing": true
}