[PATCH v3 RESEND] f2fs: add check for deleted inode

[Chao Yu]

From: Leo Stone <leocstone@xxxxxxxxx>

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.

[Chao Yu: rebase the code]
Reported-by: syzbot+b01a36acd7007e273a83@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=b01a36acd7007e273a83
Fixes: 39a53e0ce0df ("f2fs: add superblock and major in-memory structure")
Signed-off-by: Leo Stone <leocstone@xxxxxxxxx>
Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
---
- no logic change, just rebase the code to last dev-test branch
 fs/f2fs/inode.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index d6ad7810df69..543fb942bec1 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -386,6 +386,12 @@ static bool sanity_check_inode(struct inode *inode, struct page *node_page)
 		}
 	}
 
+	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;
 }
 
-- 
2.48.1.502.g6dc24dfdaf-goog