FAILED: patch "[PATCH] f2fs: fix to avoid UAF in f2fs_write_end_io()" failed to apply to 6.1-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.1-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 <stable@vger.kernel.org>.

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-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x ce2739e482bce8d2c014d76c4531c877f382aa54
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026021710-numerator-smoking-8f19@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From ce2739e482bce8d2c014d76c4531c877f382aa54 Mon Sep 17 00:00:00 2001
From: Chao Yu <chao@kernel.org>
Date: Wed, 7 Jan 2026 19:22:18 +0800
Subject: [PATCH] f2fs: fix to avoid UAF in f2fs_write_end_io()

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>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 2e133a723b99..f461f1318b4c 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -378,14 +378,20 @@ 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);
 }