[CRYPTO]: Zero out tfm before freeing in crypto_free_tfm().

Based upon discussions with Ulrich Kuehn
(ukuehn@acm.org)
Signed-off-by: James Morris <jmorris@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

crypto/api.c

@@ -155,8 +155,12 @@ struct crypto_tfm *crypto_alloc_tfm(const char *name, u32 flags)
 
 void crypto_free_tfm(struct crypto_tfm *tfm)
 {
+	struct crypto_alg *alg = tfm->__crt_alg;
+	int size = sizeof(*tfm) + alg->cra_ctxsize;
+
 	crypto_exit_ops(tfm);
-	crypto_alg_put(tfm->__crt_alg);
+	crypto_alg_put(alg);
+	memset(tfm, 0, size);
 	kfree(tfm);
 }