[PATCH 5.15.y 2/2] udf: Verify inode link counts before performing rename

[Sukrut Heroorkar <hsukrut3@gmail.com>]

From: Jan Kara <jack@suse.cz>

[ Upstream commit 6756af923e06aa33ad8894aaecbf9060953ba00f ]

During rename, we are updating link counts of various inodes either when
rename deletes target or when moving directory across directories.
Verify involved link counts are sane so that we don't trip warnings in
VFS.

Reported-by: syzbot+3ff7365dc04a6bcafa66@syzkaller.appspotmail.com
Signed-off-by: Jan Kara <jack@suse.cz>
Tested-by: syzbot+99bb36d7a3ea562b950e@syzkaller.appspotmail.com
Signed-off-by: Sukrut Heroorkar <hsukrut3@gmail.com>
---
 fs/udf/namei.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/udf/namei.c b/fs/udf/namei.c
index f4aded54a994..cb98f2d88f40 100644
--- a/fs/udf/namei.c
+++ b/fs/udf/namei.c
@@ -773,8 +773,18 @@ static int udf_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
 			retval = -ENOTEMPTY;
 			if (!empty_dir(new_inode))
 				goto out_oiter;
+			retval = -EFSCORRUPTED;
+			if (new_inode->i_nlink != 2)
+				goto out_oiter;
 		}
+		retval = -EFSCORRUPTED;
+		if (old_dir->i_nlink < 3)
+			goto out_oiter;
 		is_dir = true;
+	} else if (new_inode) {
+		retval = -EFSCORRUPTED;
+		if (new_inode->i_nlink < 1)
+			goto out_oiter;
 	}
 	if (is_dir && old_dir != new_dir) {
 		retval = udf_fiiter_find_entry(old_inode, &dotdot_name,
-- 
2.43.0