[PATCH] f2fs: evict: truncate page cache before clear_inode

[Taerang Kim <kth5965@gmail.com>]

syzbot reports a BUG_ON(inode->i_data.nrpages) in clear_inode() when
mounting a corrupted f2fs image.

I agree with Dmitry's RFC that dropping page #0 in f2fs_truncate()
can address this reproducer, since f2fs_convert_inline_inode() may
grab page #0 via f2fs_grab_cache_folio() and leave it cached on the
clear_out success path.

However, clear_inode() requires the inode mapping to be empty, and it
is hard to guarantee that the page cache can only be populated from
this truncate/inline-conversion path.
Make f2fs_evict_inode() defensively truncate any remaining page cache
before calling clear_inode(), so nrpages is guaranteed to be 0
regardless of how the cache was populated.

Link: https://lore.kernel.org/linux-f2fs-devel/20260206092958.578191-1-dmantipov@yandex.ru/
Reported-by: syzbot+fc026e87558558f75c00@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=fc026e87558558f75c00
Signed-off-by: Taerang Kim <kth5965@gmail.com>
---
 fs/f2fs/inode.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 38b8994bc1b2..5527bd76f62a 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -1001,6 +1001,13 @@ void f2fs_evict_inode(struct inode *inode)
 out_clear:
 	fscrypt_put_encryption_info(inode);
 	fsverity_cleanup_inode(inode);
+	/*
+	 * Defensively truncate any remaining page cache, e.g.
+	 * f2fs_convert_inline_inode() called from f2fs_truncate()
+	 * may leave page #0 behind in the page cache when the
+	 * inline conversion takes the clear_out success path.
+	 */
+	truncate_inode_pages_final(&inode->i_data);
 	clear_inode(inode);
 }
 
-- 
2.43.0