[PATCH 5.15.y] f2fs: fix UAF caused by decrementing sbi->nr_pages[] in f2fs_write_end_io()

[Sasha Levin <sashal@kernel.org>]

From: Yongpeng Yang <yangyongpeng@xiaomi.com>

[ 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.

Cc: stable@kernel.org
Fixes: 50fa53eccf9f ("f2fs: fix to avoid broken of dnode block list")
Reported-by: syzbot+6e4cb1cac5efc96ea0ca@syzkaller.appspotmail.com
Signed-off-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
[ folio => page ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/f2fs/data.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 887e286d2c329..9b4112177168d 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -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