ext4: disallow hard-linked directory in ext4_lookup

A hard-linked directory to its parent can cause the VFS to deadlock,
and is a sign of a corrupted file system.  So detect this case in
ext4_lookup(), before the rmdir() lockup scenario can take place.

Signed-off-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index a9fd5f4..daf8260 100644 (file)
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1330,6 +1330,12 @@ static struct dentry *ext4_lookup(struct inode *dir, struct dentry *dentry, stru
                        EXT4_ERROR_INODE(dir, "bad inode number: %u", ino);
                        return ERR_PTR(-EIO);
                }
+               if (unlikely(ino == dir->i_ino)) {
+                       EXT4_ERROR_INODE(dir, "'%.*s' linked to parent dir",
+                                        dentry->d_name.len,
+                                        dentry->d_name.name);
+                       return ERR_PTR(-EIO);
+               }
                inode = ext4_iget(dir->i_sb, ino);
                if (inode == ERR_PTR(-ESTALE)) {
                        EXT4_ERROR_INODE(dir,