ecryptfs: Reject casefold directory inodes

Even though it seems to be able to resolve some names of
case-insensitive directories, the lack of d_hash and d_compare means we
end up with a broken state in the d_cache.  Considering it was never a
goal to support these two together, and we are preparing to use
d_revalidate in case-insensitive filesystems, which would make the
combination even more broken, reject any attempt to get a casefolded
inode from ecryptfs.

Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
Reviewed-by: Eric Biggers <ebiggers@google.com>

fs/ecryptfs/inode.c

@@ -78,6 +78,14 @@ static struct inode *__ecryptfs_get_inode(struct inode *lower_inode,
 
 	if (lower_inode->i_sb != ecryptfs_superblock_to_lower(sb))
 		return ERR_PTR(-EXDEV);
+
+	/* Reject dealing with casefold directories. */
+	if (IS_CASEFOLDED(lower_inode)) {
+		pr_err_ratelimited("%s: Can't handle casefolded directory.\n",
+				   __func__);
+		return ERR_PTR(-EREMOTE);
+	}
+
 	if (!igrab(lower_inode))
 		return ERR_PTR(-ESTALE);
 	inode = iget5_locked(sb, (unsigned long)lower_inode,