ubifs: don't trigger assertion on invalid no-key filename

If userspace provides an invalid fscrypt no-key filename which encodes a
hash value with any of the UBIFS node type bits set (i.e. the high 3
bits), gracefully report ENOENT rather than triggering ubifs_assert().

Test case with kvm-xfstests shell:

. fs/ubifs/config
. ~/xfstests/common/encrypt
dev=$(__blkdev_to_ubi_volume /dev/vdc)
ubiupdatevol $dev -t
mount $dev /mnt -t ubifs
mkdir /mnt/edir
xfs_io -c set_encpolicy /mnt/edir
rm /mnt/edir/_,,,,,DAAAAAAAAAAAAAAAAAAAAAAAAAA

With the bug, the following assertion fails on the 'rm' command:

[ 19.066048] UBIFS error (ubi0:0 pid 379): ubifs_assert_failed: UBIFS assert failed: !(hash & ~UBIFS_S_KEY_HASH_MASK), in fs/ubifs/key.h:170

Fixes: f4f61d2cc6d8 ("ubifs: Implement encrypted filenames")
Cc: <[e-mail]> # v4.10+
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Eric Biggers <[e-mail]>

fs/ubifs/dir.c

···
 	if (nm.hash) {
 		ubifs_assert(c, fname_len(&nm) == 0);
 		ubifs_assert(c, fname_name(&nm) == NULL);
+		if (nm.hash & ~UBIFS_S_KEY_HASH_MASK)
+			goto done; /* ENOENT */
 		dent_key_init_hash(c, &key, dir->i_ino, nm.hash);
 		err = ubifs_tnc_lookup_dh(c, &key, dent, nm.minor_hash);
 	} else {