FAILED: patch "[PATCH] ntfs3: free the sbi after a grace period" failed to apply to 6.12-stable tree

PATCH New [email protected] 2 participants 2 messages Oct 21

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author maintainer

2026-10-21 14:49 UTC #0 lore raw

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x c01b091b06412d3b1b53d8c2925f6de586c8a2fc
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026102158-quantum-annex-72cd@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From c01b091b06412d3b1b53d8c2925f6de586c8a2fc Mon Sep 17 00:00:00 2001
From: Christian Brauner <[email protected]>
Date: Fri, 9 Oct 2026 23:51:57 +0200
Subject: [PATCH] ntfs3: free the sbi after a grace period

If the "nocase" mount option ntfs3 uses custom hash and dentry compare functions. Both access ntfs3 superblock private information in rcu pathwalk. ntfs_put_super() and ntfs3_kill_sb() drop the info without any rcu delay. A lookup that's still inside the filesystem when the last reference to the mount is dropped causes a UAF. With a pathwalk held up in ntfs_d_hash() while the last reference to the mount goes away:

  BUG: KASAN: slab-use-after-free in ntfs_nls_to_utf16+0x752/0x940
  Read of size 8 at addr ff1100010453c850 by task walker/99
  Call Trace:
   <TASK>
   ntfs_nls_to_utf16+0x752/0x940
   ntfs_d_hash+0x22b/0x500
   link_path_walk+0x11ad/0x1d30
   path_lookupat+0x63/0xb00
   filename_lookup+0x1f1/0x5b0
   vfs_statx+0xd7/0x3b0
  [...]
  Allocated by task 95:
   __kmalloc_cache_noprof+0x249/0x560
   ntfs_init_fs_context+0x2db/0x5a0
   alloc_fs_context+0x52e/0xc70
  [...]
  Freed by task 98:
   kfree+0x1db/0x5b0
   deactivate_locked_super+0x9c/0xf0
   cleanup_mnt+0x9f/0x130
   task_work_run+0x131/0x250

The bug is currently masked by the grace period in namespace_unlock() for umount(2). Keep the necessary information until the filesystem private info is freed and free it with an rcu delay.

ntfs3_free_sbi() now runs from an rcu callback and drops the upcase table via ntfs_put_shared(). So switch s_shared_lock over to spin_lock_bh(). Otherwise the callback can deadlock against a task holding the lock on the same cpu.

Fixes a3a956c78efa ("fs/ntfs3: Add option "nocase"")

Cc [email protected]

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Christian Brauner (Amutable) <[email protected]>

fs/ntfs3/ntfs_fs.h +1 -0

index 5811d89d67b3..bbcd2e02bf63 100644
@@ -211,6 +211,7 @@ struct ntfs_index {
 /* Ntfs file system in-core superblock data. */
 struct ntfs_sb_info {
 	struct super_block *sb;
+	struct rcu_head rcu;
 
 	u32 discard_granularity;
 	u64 discard_granularity_mask_inv; // ~(discard_granularity_mask_inv-1)

fs/ntfs3/super.c +21 ~~-12~~

index f4a42a0c73a4..841f9068d82f 100644
@@ -196,7 +196,7 @@ void *ntfs_set_shared(void *ptr, u32 bytes)
 	void *ret = NULL;
 	int i, j = -1;
 
-	spin_lock(&s_shared_lock);
+	spin_lock_bh(&s_shared_lock);
 	for (i = 0; i < ARRAY_SIZE(s_shared); i++) {
 		if (!s_shared[i].cnt) {
 			j = i;

@@ -214,7 +214,7 @@ void *ntfs_set_shared(void *ptr, u32 bytes)
 		s_shared[j].cnt = 1;
 		ret = ptr;
 	}
-	spin_unlock(&s_shared_lock);
+	spin_unlock_bh(&s_shared_lock);
 
 	return ret;
 }

@@ -231,7 +231,7 @@ void *ntfs_put_shared(void *ptr)
 	void *ret = ptr;
 	int i;
 
-	spin_lock(&s_shared_lock);
+	spin_lock_bh(&s_shared_lock);
 	for (i = 0; i < ARRAY_SIZE(s_shared); i++) {
 		if (s_shared[i].cnt && s_shared[i].ptr == ptr) {
 			if (--s_shared[i].cnt)

@@ -239,7 +239,7 @@ void *ntfs_put_shared(void *ptr)
 			break;
 		}
 	}
-	spin_unlock(&s_shared_lock);
+	spin_unlock_bh(&s_shared_lock);
 
 	return ret;
 }

@@ -708,6 +708,8 @@ static noinline void ntfs3_put_sbi(struct ntfs_sb_info *sbi)
 
 static void ntfs3_free_sbi(struct ntfs_sb_info *sbi)
 {
+	if (sbi->options)
+		put_mount_options(sbi->options);
 	kfree(sbi->new_rec);
 	kvfree(ntfs_put_shared(sbi->upcase));
 	kvfree(sbi->def_table);

@@ -719,6 +721,11 @@ static void ntfs3_free_sbi(struct ntfs_sb_info *sbi)
 	kfree(sbi);
 }
 
+static void ntfs3_free_sbi_rcu(struct rcu_head *head)
+{
+	ntfs3_free_sbi(container_of(head, struct ntfs_sb_info, rcu));
+}
+
 static void ntfs_put_super(struct super_block *sb)
 {
 	struct ntfs_sb_info *sbi = sb->s_fs_info;

@@ -728,11 +735,11 @@ static void ntfs_put_super(struct super_block *sb)
 	/* Mark rw ntfs as clear, if possible. */
 	ntfs_set_state(sbi, NTFS_DIRTY_CLEAR);
 
-	if (sbi->options) {
-		put_mount_options(sbi->options);
-		sbi->options = NULL;
-	}
-
+	/*
+	 * The mount options stay until the sbi is freed: ->d_hash() and
+	 * ->d_compare() of a pathwalk in rcu mode read the nls table through
+	 * them.
+	 */
 	ntfs3_put_sbi(sbi);
 }

@@ -1939,9 +1946,11 @@ static void ntfs3_kill_sb(struct super_block *sb)
 
 	kill_block_super(sb);
 
-	if (sbi->options)
-		put_mount_options(sbi->options);
-	ntfs3_free_sbi(sbi);
+	/*
+	 * A pathwalk in rcu mode may still be in ->d_hash() or ->d_compare()
+	 * and read the upcase table and the nls table through the sbi.
+	 */
+	call_rcu(&sbi->rcu, ntfs3_free_sbi_rcu);
 }
 
 // clang-format off

Sasha Levin

maintainer

2026-10-21 15:58 UTC #1 lore raw

PATCH 1/1 ntfs3: free the sbi after a grace period

From: Christian Brauner <[email protected]>

[ Upstream commit c01b091b06412d3b1b53d8c2925f6de586c8a2fc ]

  BUG: KASAN: slab-use-after-free in ntfs_nls_to_utf16+0x752/0x940
  Read of size 8 at addr ff1100010453c850 by task walker/99
  Call Trace:
   <TASK>
   ntfs_nls_to_utf16+0x752/0x940
   ntfs_d_hash+0x22b/0x500
   link_path_walk+0x11ad/0x1d30
   path_lookupat+0x63/0xb00
   filename_lookup+0x1f1/0x5b0
   vfs_statx+0xd7/0x3b0
  [...]
  Allocated by task 95:
   __kmalloc_cache_noprof+0x249/0x560
   ntfs_init_fs_context+0x2db/0x5a0
   alloc_fs_context+0x52e/0xc70
  [...]
  Freed by task 98:
   kfree+0x1db/0x5b0
   deactivate_locked_super+0x9c/0xf0
   cleanup_mnt+0x9f/0x130
   task_work_run+0x131/0x250

The bug is currently masked by the grace period in namespace_unlock() for umount(2). Keep the necessary information until the filesystem private info is freed and free it with an rcu delay.

Fixes a3a956c78efa ("fs/ntfs3: Add option "nocase"")

Cc [email protected]

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Christian Brauner (Amutable) <[email protected]>

[ sashal: Adjusted ntfs_put_super() context because the early mount-options cleanup block was already absent. ]

Signed-off-by Sasha Levin <[email protected]>

---
 fs/ntfs3/ntfs_fs.h |  1 +
 fs/ntfs3/super.c   | 29 ++++++++++++++++++++++-------
 2 files changed, 23 insertions(+), 7 deletions(-)

fs/ntfs3/ntfs_fs.h +1 -0

index 11be9a6f041cf..934dcb136d6da 100644
@@ -209,6 +209,7 @@ struct ntfs_index {
 /* Ntfs file system in-core superblock data. */
 struct ntfs_sb_info {
 	struct super_block *sb;
+	struct rcu_head rcu;
 
 	u32 discard_granularity;
 	u64 discard_granularity_mask_inv; // ~(discard_granularity_mask_inv-1)

fs/ntfs3/super.c +22 -7

index 4b1941e3f3a67..c7c1896acc2c5 100644
@@ -187,7 +187,7 @@ void *ntfs_set_shared(void *ptr, u32 bytes)
 	void *ret = NULL;
 	int i, j = -1;
 
-	spin_lock(&s_shared_lock);
+	spin_lock_bh(&s_shared_lock);
 	for (i = 0; i < ARRAY_SIZE(s_shared); i++) {
 		if (!s_shared[i].cnt) {
 			j = i;

@@ -205,7 +205,7 @@ void *ntfs_set_shared(void *ptr, u32 bytes)
 		s_shared[j].cnt = 1;
 		ret = ptr;
 	}
-	spin_unlock(&s_shared_lock);
+	spin_unlock_bh(&s_shared_lock);
 
 	return ret;
 }

@@ -222,7 +222,7 @@ void *ntfs_put_shared(void *ptr)
 	void *ret = ptr;
 	int i;
 
-	spin_lock(&s_shared_lock);
+	spin_lock_bh(&s_shared_lock);
 	for (i = 0; i < ARRAY_SIZE(s_shared); i++) {
 		if (s_shared[i].cnt && s_shared[i].ptr == ptr) {
 			if (--s_shared[i].cnt)

@@ -230,7 +230,7 @@ void *ntfs_put_shared(void *ptr)
 			break;
 		}
 	}
-	spin_unlock(&s_shared_lock);
+	spin_unlock_bh(&s_shared_lock);
 
 	return ret;
 }

@@ -630,6 +630,8 @@ static noinline void ntfs3_put_sbi(struct ntfs_sb_info *sbi)
 
 static void ntfs3_free_sbi(struct ntfs_sb_info *sbi)
 {
+	if (sbi->options)
+		put_mount_options(sbi->options);
 	kfree(sbi->new_rec);
 	kvfree(ntfs_put_shared(sbi->upcase));
 	kvfree(sbi->def_table);

@@ -641,6 +643,11 @@ static void ntfs3_free_sbi(struct ntfs_sb_info *sbi)
 	kfree(sbi);
 }
 
+static void ntfs3_free_sbi_rcu(struct rcu_head *head)
+{
+	ntfs3_free_sbi(container_of(head, struct ntfs_sb_info, rcu));
+}
+
 static void ntfs_put_super(struct super_block *sb)
 {
 	struct ntfs_sb_info *sbi = sb->s_fs_info;

@@ -657,6 +664,12 @@ static void ntfs_put_super(struct super_block *sb)
 
 	/* Mark rw ntfs as clear, if possible. */
 	ntfs_set_state(sbi, NTFS_DIRTY_CLEAR);
+
+	/*
+	 * The mount options stay until the sbi is freed: ->d_hash() and
+	 * ->d_compare() of a pathwalk in rcu mode read the nls table through
+	 * them.
+	 */
 	ntfs3_put_sbi(sbi);
 }

@@ -1806,9 +1819,11 @@ static void ntfs3_kill_sb(struct super_block *sb)
 
 	kill_block_super(sb);
 
-	if (sbi->options)
-		put_mount_options(sbi->options);
-	ntfs3_free_sbi(sbi);
+	/*
+	 * A pathwalk in rcu mode may still be in ->d_hash() or ->d_compare()
+	 * and read the upcase table and the nls table through the sbi.
+	 */
+	call_rcu(&sbi->rcu, ntfs3_free_sbi_rcu);
 }
 
 // clang-format off

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