FAILED: patch "[PATCH] f2fs: fix UAF caused by decrementing sbi->nr_pages[] in" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 2d9c4a4ed4eef1f82c5b16b037aee8bad819fd53
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026042434-undead-bronzing-dd24@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From 2d9c4a4ed4eef1f82c5b16b037aee8bad819fd53 Mon Sep 17 00:00:00 2001
From: Yongpeng Yang <[email protected]>
Date: Fri, 27 Feb 2026 15:30:52 +0800
Subject: [PATCH] f2fs: fix UAF caused by decrementing sbi->nr_pages[] in
f2fs_write_end_io()

The xfstests case "generic/107" and syzbot have both reported a NULL pointer dereference.

The concurrent scenario that triggers the panic is as follows:

F2FS_WB_CP_DATA write callback umount
- f2fs_write_checkpoint
- f2fs_wait_on_all_pages(sbi, F2FS_WB_CP_DATA)
- blk_mq_end_request
- bio_endio
- f2fs_write_end_io
: dec_page_count(sbi, F2FS_WB_CP_DATA)
: wake_up(&sbi->cp_wait)
- kill_f2fs_super
- kill_block_super
- f2fs_put_super
: iput(sbi->node_inode)
: sbi->node_inode = NULL
: f2fs_in_warm_node_list
- is_node_folio // sbi->node_inode is NULL and panic

The root cause is that f2fs_put_super() calls iput(sbi->node_inode) and sets sbi->node_inode to NULL after sbi->nr_pages[F2FS_WB_CP_DATA] is decremented to zero. As a result, f2fs_in_warm_node_list() may dereference a NULL node_inode when checking whether a folio belongs to the node inode, leading to a panic.

This patch fixes the issue by calling f2fs_in_warm_node_list() before decrementing sbi->nr_pages[F2FS_WB_CP_DATA], thus preventing the use-after-free condition.

index 400f0400e13d..57fc9bad31bf 100644
@@ -386,6 +386,8 @@ static void f2fs_write_end_io(struct bio *bio)
 				folio->index, NODE_TYPE_REGULAR, true);
 			f2fs_bug_on(sbi, folio->index != nid_of_node(folio));
 		}
+		if (f2fs_in_warm_node_list(sbi, folio))
+			f2fs_del_fsync_node_entry(sbi, folio);
 
 		dec_page_count(sbi, type);
 

@@ -397,8 +399,6 @@ static void f2fs_write_end_io(struct bio *bio)
 				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);
 	}

From: Yongpeng Yang <[email protected]>

[ Upstream commit 2d9c4a4ed4eef1f82c5b16b037aee8bad819fd53 ]

The xfstests case "generic/107" and syzbot have both reported a NULL pointer dereference.

The concurrent scenario that triggers the panic is as follows:

F2FS_WB_CP_DATA write callback umount
- f2fs_write_checkpoint
- f2fs_wait_on_all_pages(sbi, F2FS_WB_CP_DATA)
- blk_mq_end_request
- bio_endio
- f2fs_write_end_io
: dec_page_count(sbi, F2FS_WB_CP_DATA)
: wake_up(&sbi->cp_wait)
- kill_f2fs_super
- kill_block_super
- f2fs_put_super
: iput(sbi->node_inode)
: sbi->node_inode = NULL
: f2fs_in_warm_node_list
- is_node_folio // sbi->node_inode is NULL and panic

The root cause is that f2fs_put_super() calls iput(sbi->node_inode) and sets sbi->node_inode to NULL after sbi->nr_pages[F2FS_WB_CP_DATA] is decremented to zero. As a result, f2fs_in_warm_node_list() may dereference a NULL node_inode when checking whether a folio belongs to the node inode, leading to a panic.

This patch fixes the issue by calling f2fs_in_warm_node_list() before decrementing sbi->nr_pages[F2FS_WB_CP_DATA], thus preventing the use-after-free condition.

---
 fs/f2fs/data.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 887e286d2c329..9b4112177168d 100644
@@ -339,6 +339,8 @@ static void f2fs_write_end_io(struct bio *bio)
 
 		f2fs_bug_on(sbi, page->mapping == NODE_MAPPING(sbi) &&
 					page->index != nid_of_node(page));
+		if (f2fs_in_warm_node_list(sbi, page))
+			f2fs_del_fsync_node_entry(sbi, page);
 
 		dec_page_count(sbi, type);
 

@@ -350,8 +352,6 @@ static void f2fs_write_end_io(struct bio *bio)
 				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);
 	}

2.53.0