* [f2fs-dev] [PATCH] f2fs: fix to avoid UAF in f2fs_write_end_io()
@ 2026-01-07 11:22 ` Chao Yu
0 siblings, 0 replies; 6+ messages in thread
From: Chao Yu via Linux-f2fs-devel @ 2026-01-07 11:22 UTC (permalink / raw)
To: jaegeuk; +Cc: syzbot+b4444e3c972a7a124187, stable, linux-kernel,
linux-f2fs-devel
As syzbot reported an use-after-free issue in f2fs_write_end_io().
It is caused by below race condition:
loop device umount
- worker_thread
- loop_process_work
- do_req_filebacked
- lo_rw_aio
- lo_rw_aio_complete
- blk_mq_end_request
- blk_update_request
- f2fs_write_end_io
- dec_page_count
- folio_end_writeback
- kill_f2fs_super
- kill_block_super
- f2fs_put_super
: free(sbi)
: get_pages(, F2FS_WB_CP_DATA)
accessed sbi which is freed
In kill_f2fs_super(), we will drop all page caches of f2fs inodes before
call free(sbi), it guarantee that all folios should end its writeback, so
it should be safe to access sbi before last folio_end_writeback().
Let's relocate ckpt thread wakeup flow before folio_end_writeback() to
resolve this issue.
Cc: stable@kernel.org
Fixes: e234088758fc ("f2fs: avoid wait if IO end up when do_checkpoint for better performance")
Reported-by: syzbot+b4444e3c972a7a124187@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b4444e3c972a7a124187
Signed-off-by: Chao Yu <chao@kernel.org>
---
fs/f2fs/data.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index c30e69392a62..8550c964b71c 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -356,14 +356,20 @@ static void f2fs_write_end_io(struct bio *bio)
folio->index != nid_of_node(folio));
dec_page_count(sbi, type);
+
+ /*
+ * we should access sbi before folio_end_writeback() to
+ * avoid racing w/ kill_f2fs_super()
+ */
+ if (type == F2FS_WB_CP_DATA && !get_pages(sbi, type) &&
+ wq_has_sleeper(&sbi->cp_wait))
+ wake_up(&sbi->cp_wait);
+
if (f2fs_in_warm_node_list(sbi, folio))
f2fs_del_fsync_node_entry(sbi, folio);
folio_clear_f2fs_gcing(folio);
folio_end_writeback(folio);
}
- if (!get_pages(sbi, F2FS_WB_CP_DATA) &&
- wq_has_sleeper(&sbi->cp_wait))
- wake_up(&sbi->cp_wait);
bio_put(bio);
}
--
2.40.1
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Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH] f2fs: fix to avoid UAF in f2fs_write_end_io()
@ 2026-01-07 11:22 ` Chao Yu
0 siblings, 0 replies; 6+ messages in thread
From: Chao Yu @ 2026-01-07 11:22 UTC (permalink / raw)
To: jaegeuk
Cc: linux-f2fs-devel, linux-kernel, Chao Yu, stable,
syzbot+b4444e3c972a7a124187
As syzbot reported an use-after-free issue in f2fs_write_end_io().
It is caused by below race condition:
loop device umount
- worker_thread
- loop_process_work
- do_req_filebacked
- lo_rw_aio
- lo_rw_aio_complete
- blk_mq_end_request
- blk_update_request
- f2fs_write_end_io
- dec_page_count
- folio_end_writeback
- kill_f2fs_super
- kill_block_super
- f2fs_put_super
: free(sbi)
: get_pages(, F2FS_WB_CP_DATA)
accessed sbi which is freed
In kill_f2fs_super(), we will drop all page caches of f2fs inodes before
call free(sbi), it guarantee that all folios should end its writeback, so
it should be safe to access sbi before last folio_end_writeback().
Let's relocate ckpt thread wakeup flow before folio_end_writeback() to
resolve this issue.
Cc: stable@kernel.org
Fixes: e234088758fc ("f2fs: avoid wait if IO end up when do_checkpoint for better performance")
Reported-by: syzbot+b4444e3c972a7a124187@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b4444e3c972a7a124187
Signed-off-by: Chao Yu <chao@kernel.org>
---
fs/f2fs/data.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index c30e69392a62..8550c964b71c 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -356,14 +356,20 @@ static void f2fs_write_end_io(struct bio *bio)
folio->index != nid_of_node(folio));
dec_page_count(sbi, type);
+
+ /*
+ * we should access sbi before folio_end_writeback() to
+ * avoid racing w/ kill_f2fs_super()
+ */
+ if (type == F2FS_WB_CP_DATA && !get_pages(sbi, type) &&
+ wq_has_sleeper(&sbi->cp_wait))
+ wake_up(&sbi->cp_wait);
+
if (f2fs_in_warm_node_list(sbi, folio))
f2fs_del_fsync_node_entry(sbi, folio);
folio_clear_f2fs_gcing(folio);
folio_end_writeback(folio);
}
- if (!get_pages(sbi, F2FS_WB_CP_DATA) &&
- wq_has_sleeper(&sbi->cp_wait))
- wake_up(&sbi->cp_wait);
bio_put(bio);
}
--
2.40.1
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [f2fs-dev] [PATCH] f2fs: fix to avoid UAF in f2fs_write_end_io()
2026-01-07 11:22 ` Chao Yu
@ 2026-01-19 13:50 ` patchwork-bot+f2fs
-1 siblings, 0 replies; 6+ messages in thread
From: patchwork-bot+f2fs--- via Linux-f2fs-devel @ 2026-01-19 13:50 UTC (permalink / raw)
To: Chao Yu
Cc: syzbot+b4444e3c972a7a124187, jaegeuk, linux-f2fs-devel, stable,
linux-kernel
Hello:
This patch was applied to jaegeuk/f2fs.git (dev)
by Jaegeuk Kim <jaegeuk@kernel.org>:
On Wed, 7 Jan 2026 19:22:18 +0800 you wrote:
> As syzbot reported an use-after-free issue in f2fs_write_end_io().
>
> It is caused by below race condition:
>
> loop device umount
> - worker_thread
> - loop_process_work
> - do_req_filebacked
> - lo_rw_aio
> - lo_rw_aio_complete
> - blk_mq_end_request
> - blk_update_request
> - f2fs_write_end_io
> - dec_page_count
> - folio_end_writeback
> - kill_f2fs_super
> - kill_block_super
> - f2fs_put_super
> : free(sbi)
> : get_pages(, F2FS_WB_CP_DATA)
> accessed sbi which is freed
>
> [...]
Here is the summary with links:
- [f2fs-dev] f2fs: fix to avoid UAF in f2fs_write_end_io()
https://git.kernel.org/jaegeuk/f2fs/c/ce2739e482bc
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
_______________________________________________
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Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [f2fs-dev] [PATCH] f2fs: fix to avoid UAF in f2fs_write_end_io()
@ 2026-01-19 13:50 ` patchwork-bot+f2fs
0 siblings, 0 replies; 6+ messages in thread
From: patchwork-bot+f2fs @ 2026-01-19 13:50 UTC (permalink / raw)
To: Chao Yu
Cc: jaegeuk, syzbot+b4444e3c972a7a124187, stable, linux-kernel,
linux-f2fs-devel
Hello:
This patch was applied to jaegeuk/f2fs.git (dev)
by Jaegeuk Kim <jaegeuk@kernel.org>:
On Wed, 7 Jan 2026 19:22:18 +0800 you wrote:
> As syzbot reported an use-after-free issue in f2fs_write_end_io().
>
> It is caused by below race condition:
>
> loop device umount
> - worker_thread
> - loop_process_work
> - do_req_filebacked
> - lo_rw_aio
> - lo_rw_aio_complete
> - blk_mq_end_request
> - blk_update_request
> - f2fs_write_end_io
> - dec_page_count
> - folio_end_writeback
> - kill_f2fs_super
> - kill_block_super
> - f2fs_put_super
> : free(sbi)
> : get_pages(, F2FS_WB_CP_DATA)
> accessed sbi which is freed
>
> [...]
Here is the summary with links:
- [f2fs-dev] f2fs: fix to avoid UAF in f2fs_write_end_io()
https://git.kernel.org/jaegeuk/f2fs/c/ce2739e482bc
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [f2fs-dev] [PATCH] f2fs: fix to avoid UAF in f2fs_write_end_io()
2026-01-07 11:22 ` Chao Yu
@ 2026-03-02 1:31 ` Guenter Roeck
-1 siblings, 0 replies; 6+ messages in thread
From: Guenter Roeck @ 2026-03-02 1:31 UTC (permalink / raw)
To: Chao Yu
Cc: syzbot+b4444e3c972a7a124187, jaegeuk, linux-f2fs-devel, stable,
linux-kernel
Hi,
On Wed, Jan 07, 2026 at 07:22:18PM +0800, Chao Yu wrote:
> As syzbot reported an use-after-free issue in f2fs_write_end_io().
>
> It is caused by below race condition:
>
> loop device umount
> - worker_thread
> - loop_process_work
> - do_req_filebacked
> - lo_rw_aio
> - lo_rw_aio_complete
> - blk_mq_end_request
> - blk_update_request
> - f2fs_write_end_io
> - dec_page_count
> - folio_end_writeback
> - kill_f2fs_super
> - kill_block_super
> - f2fs_put_super
> : free(sbi)
> : get_pages(, F2FS_WB_CP_DATA)
> accessed sbi which is freed
>
> In kill_f2fs_super(), we will drop all page caches of f2fs inodes before
> call free(sbi), it guarantee that all folios should end its writeback, so
> it should be safe to access sbi before last folio_end_writeback().
>
> Let's relocate ckpt thread wakeup flow before folio_end_writeback() to
> resolve this issue.
>
> Cc: stable@kernel.org
> Fixes: e234088758fc ("f2fs: avoid wait if IO end up when do_checkpoint for better performance")
> Reported-by: syzbot+b4444e3c972a7a124187@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=b4444e3c972a7a124187
> Signed-off-by: Chao Yu <chao@kernel.org>
> ---
> fs/f2fs/data.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index c30e69392a62..8550c964b71c 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -356,14 +356,20 @@ static void f2fs_write_end_io(struct bio *bio)
> folio->index != nid_of_node(folio));
>
From the code:
#ifdef CONFIG_F2FS_FS_COMPRESSION
if (f2fs_is_compressed_page(folio)) {
f2fs_compress_write_end_io(bio, folio);
continue;
}
#endif
...
> dec_page_count(sbi, type);
> +
> + /*
> + * we should access sbi before folio_end_writeback() to
> + * avoid racing w/ kill_f2fs_super()
> + */
> + if (type == F2FS_WB_CP_DATA && !get_pages(sbi, type) &&
> + wq_has_sleeper(&sbi->cp_wait))
> + wake_up(&sbi->cp_wait);
> +
As the above snippet shows, the wakeup logic is now skipped for compressed
pages, and may be skipped entirely if the last page is a compressed page.
Also, givven that f2fs_compress_write_end_io() is kind of similar to the
code below for compressed pages, does that mean that there is a similar
potential UAF vulnerability for compressed pages in that function ?
Thanks,
Guenter
> if (f2fs_in_warm_node_list(sbi, folio))
> f2fs_del_fsync_node_entry(sbi, folio);
> folio_clear_f2fs_gcing(folio);
> folio_end_writeback(folio);
> }
> - if (!get_pages(sbi, F2FS_WB_CP_DATA) &&
> - wq_has_sleeper(&sbi->cp_wait))
> - wake_up(&sbi->cp_wait);
>
> bio_put(bio);
> }
_______________________________________________
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [f2fs-dev] [PATCH] f2fs: fix to avoid UAF in f2fs_write_end_io()
@ 2026-03-02 1:31 ` Guenter Roeck
0 siblings, 0 replies; 6+ messages in thread
From: Guenter Roeck @ 2026-03-02 1:31 UTC (permalink / raw)
To: Chao Yu
Cc: jaegeuk, syzbot+b4444e3c972a7a124187, stable, linux-kernel,
linux-f2fs-devel
Hi,
On Wed, Jan 07, 2026 at 07:22:18PM +0800, Chao Yu wrote:
> As syzbot reported an use-after-free issue in f2fs_write_end_io().
>
> It is caused by below race condition:
>
> loop device umount
> - worker_thread
> - loop_process_work
> - do_req_filebacked
> - lo_rw_aio
> - lo_rw_aio_complete
> - blk_mq_end_request
> - blk_update_request
> - f2fs_write_end_io
> - dec_page_count
> - folio_end_writeback
> - kill_f2fs_super
> - kill_block_super
> - f2fs_put_super
> : free(sbi)
> : get_pages(, F2FS_WB_CP_DATA)
> accessed sbi which is freed
>
> In kill_f2fs_super(), we will drop all page caches of f2fs inodes before
> call free(sbi), it guarantee that all folios should end its writeback, so
> it should be safe to access sbi before last folio_end_writeback().
>
> Let's relocate ckpt thread wakeup flow before folio_end_writeback() to
> resolve this issue.
>
> Cc: stable@kernel.org
> Fixes: e234088758fc ("f2fs: avoid wait if IO end up when do_checkpoint for better performance")
> Reported-by: syzbot+b4444e3c972a7a124187@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=b4444e3c972a7a124187
> Signed-off-by: Chao Yu <chao@kernel.org>
> ---
> fs/f2fs/data.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index c30e69392a62..8550c964b71c 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -356,14 +356,20 @@ static void f2fs_write_end_io(struct bio *bio)
> folio->index != nid_of_node(folio));
>
From the code:
#ifdef CONFIG_F2FS_FS_COMPRESSION
if (f2fs_is_compressed_page(folio)) {
f2fs_compress_write_end_io(bio, folio);
continue;
}
#endif
...
> dec_page_count(sbi, type);
> +
> + /*
> + * we should access sbi before folio_end_writeback() to
> + * avoid racing w/ kill_f2fs_super()
> + */
> + if (type == F2FS_WB_CP_DATA && !get_pages(sbi, type) &&
> + wq_has_sleeper(&sbi->cp_wait))
> + wake_up(&sbi->cp_wait);
> +
As the above snippet shows, the wakeup logic is now skipped for compressed
pages, and may be skipped entirely if the last page is a compressed page.
Also, givven that f2fs_compress_write_end_io() is kind of similar to the
code below for compressed pages, does that mean that there is a similar
potential UAF vulnerability for compressed pages in that function ?
Thanks,
Guenter
> if (f2fs_in_warm_node_list(sbi, folio))
> f2fs_del_fsync_node_entry(sbi, folio);
> folio_clear_f2fs_gcing(folio);
> folio_end_writeback(folio);
> }
> - if (!get_pages(sbi, F2FS_WB_CP_DATA) &&
> - wq_has_sleeper(&sbi->cp_wait))
> - wake_up(&sbi->cp_wait);
>
> bio_put(bio);
> }
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2026-03-02 1:31 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
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2026-01-07 11:22 [f2fs-dev] [PATCH] f2fs: fix to avoid UAF in f2fs_write_end_io() Chao Yu via Linux-f2fs-devel
2026-01-07 11:22 ` Chao Yu
2026-01-19 13:50 ` [f2fs-dev] " patchwork-bot+f2fs--- via Linux-f2fs-devel
2026-01-19 13:50 ` patchwork-bot+f2fs
2026-03-02 1:31 ` Guenter Roeck
2026-03-02 1:31 ` Guenter Roeck
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