Re: [PATCH] f2fs: Add check for deleted inode

From: Chao Yu
Date: Mon Nov 25 2024 - 07:54:27 EST


On 2024/11/24 9:04, Leo Stone wrote:
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@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=b01a36acd7007e273a83
Fixes: 4c8ff7095bef ("f2fs: support data compression")

Hello Leo,

I'm fine w/ this change, but I didn't get it, how did above commit introduce
this bug?

Thanks,

Signed-off-by: Leo Stone <leocstone@xxxxxxxxx>
---
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;
}