[PATCH 5.15] ext4: fix timer use-after-free on failed mount

[PATCH 5.15] ext4: fix timer use-after-free on failed mount

[Xiangyu Chen]

From: Xiaxi Shen <shenxiaxi26@gmail.com>

commit 0ce160c5bdb67081a62293028dc85758a8efb22a upstream.

Syzbot has found an ODEBUG bug in ext4_fill_super

The del_timer_sync function cancels the s_err_report timer,
which reminds about filesystem errors daily. We should
guarantee the timer is no longer active before kfree(sbi).

When filesystem mounting fails, the flow goes to failed_mount3,
where an error occurs when ext4_stop_mmpd is called, causing
a read I/O failure. This triggers the ext4_handle_error function
that ultimately re-arms the timer,
leaving the s_err_report timer active before kfree(sbi) is called.

Fix the issue by canceling the s_err_report timer after calling ext4_stop_mmpd.

Signed-off-by: Xiaxi Shen <shenxiaxi26@gmail.com>
Reported-and-tested-by: syzbot+59e0101c430934bc9a36@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=59e0101c430934bc9a36
Link: https://patch.msgid.link/20240715043336.98097-1-shenxiaxi26@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
[Minor context change fixed]
Signed-off-by: Xiangyu Chen <xiangyu.chen@windriver.com>
Signed-off-by: He Zhe <zhe.he@windriver.com>
---
Verified the build test.
---
 fs/ext4/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 126b582d85fc..8f33b6db8aae 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5085,8 +5085,8 @@ failed_mount9: __maybe_unused
 failed_mount3:
 	/* flush s_error_work before sbi destroy */
 	flush_work(&sbi->s_error_work);
-	del_timer_sync(&sbi->s_err_report);
 	ext4_stop_mmpd(sbi);
+	del_timer_sync(&sbi->s_err_report);
 failed_mount2:
 	rcu_read_lock();
 	group_desc = rcu_dereference(sbi->s_group_desc);
-- 
2.34.1

[PATCH 5.10] ext4: fix timer use-after-free on failed mount

[Xiangyu Chen]

From: Xiaxi Shen <shenxiaxi26@gmail.com>

commit 0ce160c5bdb67081a62293028dc85758a8efb22a upstream.

Syzbot has found an ODEBUG bug in ext4_fill_super

The del_timer_sync function cancels the s_err_report timer,
which reminds about filesystem errors daily. We should
guarantee the timer is no longer active before kfree(sbi).

When filesystem mounting fails, the flow goes to failed_mount3,
where an error occurs when ext4_stop_mmpd is called, causing
a read I/O failure. This triggers the ext4_handle_error function
that ultimately re-arms the timer,
leaving the s_err_report timer active before kfree(sbi) is called.

Fix the issue by canceling the s_err_report timer after calling ext4_stop_mmpd.

Signed-off-by: Xiaxi Shen <shenxiaxi26@gmail.com>
Reported-and-tested-by: syzbot+59e0101c430934bc9a36@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=59e0101c430934bc9a36
Link: https://patch.msgid.link/20240715043336.98097-1-shenxiaxi26@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
[Minor context change fixed]
Signed-off-by: Xiangyu Chen <xiangyu.chen@windriver.com>
Signed-off-by: He Zhe <zhe.he@windriver.com>
---
Verified the build test.
---
 fs/ext4/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 9d7800d66200..522a5d85fbf5 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5185,8 +5185,8 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 failed_mount3a:
 	ext4_es_unregister_shrinker(sbi);
 failed_mount3:
-	del_timer_sync(&sbi->s_err_report);
 	ext4_stop_mmpd(sbi);
+	del_timer_sync(&sbi->s_err_report);
 failed_mount2:
 	rcu_read_lock();
 	group_desc = rcu_dereference(sbi->s_group_desc);
-- 
2.34.1

Re: [PATCH 5.15] ext4: fix timer use-after-free on failed mount

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: 0ce160c5bdb67081a62293028dc85758a8efb22a

WARNING: Author mismatch between patch and upstream commit:
Backport author: Xiangyu Chen<xiangyu.chen@eng.windriver.com>
Commit author: Xiaxi Shen<shenxiaxi26@gmail.com>

Status in newer kernel trees:
6.14.y | Present (exact SHA1)
6.13.y | Present (exact SHA1)
6.12.y | Present (exact SHA1)
6.6.y | Present (different SHA1: 9203817ba46e)
6.1.y | Present (different SHA1: cf3196e5e2f3)

Note: The patch differs from the upstream commit:
---
1:  0ce160c5bdb67 < -:  ------------- ext4: fix timer use-after-free on failed mount
-:  ------------- > 1:  806747a29525d ext4: fix timer use-after-free on failed mount
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-5.15.y       |  Success    |  Success   |

Re: [PATCH 5.10] ext4: fix timer use-after-free on failed mount

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: 0ce160c5bdb67081a62293028dc85758a8efb22a

WARNING: Author mismatch between patch and upstream commit:
Backport author: Xiangyu Chen<xiangyu.chen@eng.windriver.com>
Commit author: Xiaxi Shen<shenxiaxi26@gmail.com>

Status in newer kernel trees:
6.14.y | Present (exact SHA1)
6.13.y | Present (exact SHA1)
6.12.y | Present (exact SHA1)
6.6.y | Present (different SHA1: 9203817ba46e)
6.1.y | Present (different SHA1: cf3196e5e2f3)
5.15.y | Present (different SHA1: 2a4ae3bcdf05)

Note: The patch differs from the upstream commit:
---
1:  0ce160c5bdb67 < -:  ------------- ext4: fix timer use-after-free on failed mount
-:  ------------- > 1:  1c2c1669ad83f ext4: fix timer use-after-free on failed mount
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-5.10.y       |  Success    |  Success   |