crypto: algif_aead - fix AIO handling of zero buffer

Handle the case when the caller provided a zero buffer to
sendmsg/sendpage. Such scenario is legal for AEAD ciphers when no
plaintext / ciphertext and no AAD is provided and the caller only
requests the generation of the tag value.
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/algif_aead.c

@@ -448,12 +448,13 @@ static int aead_recvmsg_async(struct socket *sock, struct msghdr *msg,
 	used -= ctx->aead_assoclen + (ctx->enc ? as : 0);
 
 	/* take over all tx sgls from ctx */
-	areq->tsgl = sock_kmalloc(sk, sizeof(*areq->tsgl) * sgl->cur,
+	areq->tsgl = sock_kmalloc(sk,
+				  sizeof(*areq->tsgl) * max_t(u32, sgl->cur, 1),
 				  GFP_KERNEL);
 	if (unlikely(!areq->tsgl))
 		goto free;
 
-	sg_init_table(areq->tsgl, sgl->cur);
+	sg_init_table(areq->tsgl, max_t(u32, sgl->cur, 1));
 	for (i = 0; i < sgl->cur; i++)
 		sg_set_page(&areq->tsgl[i], sg_page(&sgl->sg[i]),
 			    sgl->sg[i].length, sgl->sg[i].offset);