dm crypt: fix free of bad values after tfm allocation failure

commit 5d0be84e upstream.

If crypt_alloc_tfms() had to allocate multiple tfms and it failed before
the last allocation, then it would call crypt_free_tfms() and could free
pointers from uninitialized memory -- due to the crypt_free_tfms() check
for non-zero cc->tfms[i].  Fix by allocating zeroed memory.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/md/dm-crypt.c

@@ -1400,7 +1400,7 @@ static int crypt_alloc_tfms(struct crypt_config *cc, char *ciphermode)
 	unsigned i;
 	int err;
 
-	cc->tfms = kmalloc(cc->tfms_count * sizeof(struct crypto_ablkcipher *),
+	cc->tfms = kzalloc(cc->tfms_count * sizeof(struct crypto_ablkcipher *),
 			   GFP_KERNEL);
 	if (!cc->tfms)
 		return -ENOMEM;