[PATCH v5] f2fs: add check for deleted inode

[Chao Yu <chao@kernel.org>]

From: Leo Stone <leocstone@gmail.com>

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 and fix orphan inode recovery issue]
Reported-by: syzbot+b01a36acd7007e273a83@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b01a36acd7007e273a83
Fixes: 39a53e0ce0df ("f2fs: add superblock and major in-memory structure")
Signed-off-by: Leo Stone <leocstone@gmail.com>
Signed-off-by: Chao Yu <chao@kernel.org>
---
v5:
- only check i_nlink in lookup()
 fs/f2fs/namei.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
index 949621bc0d07..e39533482b45 100644
--- a/fs/f2fs/namei.c
+++ b/fs/f2fs/namei.c
@@ -502,6 +502,14 @@ static struct dentry *f2fs_lookup(struct inode *dir, struct dentry *dentry,
 		goto out;
 	}
 
+	if (inode->i_nlink == 0) {
+		f2fs_warn(F2FS_I_SB(inode), "%s: inode (ino=%lx) has zero i_nlink",
+			  __func__, inode->i_ino);
+		err = -EFSCORRUPTED;
+		set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
+		goto out_iput;
+	}
+
 	if (IS_ENCRYPTED(dir) &&
 	    (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) &&
 	    !fscrypt_has_permitted_context(dir, inode)) {
-- 
2.40.1