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

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 <[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-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x ce2739e482bce8d2c014d76c4531c877f382aa54
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --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 <[email protected]>
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.

index 2e133a723b99..f461f1318b4c 100644
@@ -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);
 }

From: Chao Yu <[email protected]>

[ Upstream commit ce2739e482bce8d2c014d76c4531c877f382aa54 ]

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.

---
 fs/f2fs/data.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

index 3bf3b24e38d23..0e13b01db06aa 100644
@@ -358,14 +358,20 @@ static void f2fs_write_end_io(struct bio *bio)
 					page->index != nid_of_node(page));
 
 		dec_page_count(sbi, type);
+
+		/*
+		 * we should access sbi before end_page_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, page))
 			f2fs_del_fsync_node_entry(sbi, page);
 		clear_page_private_gcing(page);
 		end_page_writeback(page);
 	}
-	if (!get_pages(sbi, F2FS_WB_CP_DATA) &&
-				wq_has_sleeper(&sbi->cp_wait))
-		wake_up(&sbi->cp_wait);
 
 	bio_put(bio);
 }

2.51.0