[PATCH] f2fs: Add check for deleted inode

[PATCH] f2fs: Add check for deleted inode

[Leo Stone]

The syzbot reproducer mounts a f2fs image, then tries to unlink an
existing file. However, the unlinked file already has a link count of 0
when it is read for the first time in do_read_inode().

Add a check to sanity_check_inode() for i_nlink == 0.

#syz test

Reported-by: syzbot+b01a36acd7007e273a83@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b01a36acd7007e273a83
Fixes: 4c8ff7095bef ("f2fs: support data compression")
Signed-off-by: Leo Stone <leocstone@gmail.com>
---
 fs/f2fs/inode.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 1ed86df343a5..65f1dc32f173 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -372,6 +372,12 @@ static bool sanity_check_inode(struct inode *inode, struct page *node_page)
 		return false;
 	}
 
+	if (inode->i_nlink == 0) {
+		f2fs_warn(sbi, "%s: inode (ino=%lx) has a link count of 0",
+			  __func__, inode->i_ino);
+		return false;
+	}
+
 	return true;
 }
 
-- 
2.43.0

Re: [syzbot] [f2fs?] WARNING in f2fs_unlink

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+b01a36acd7007e273a83@syzkaller.appspotmail.com
Tested-by: syzbot+b01a36acd7007e273a83@syzkaller.appspotmail.com

Tested on:

commit:         9f16d5e6 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14d40778580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e92fc420ca55fe33
dashboard link: https://syzkaller.appspot.com/bug?extid=b01a36acd7007e273a83
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=15dd69c0580000

Note: testing is done by a robot and is best-effort only.