tls: Skip zerocopy path for ITER_KVEC

The zerocopy path ultimately calls iov_iter_get_pages, which defines the
step function for ITER_KVECs as simply, return -EFAULT. Taking the
non-zerocopy path for ITER_KVECs avoids the unnecessary fallback.

See https://lore.kernel.org/lkml/20150401023311.GL29656@ZenIV.linux.org.uk/T/#u
for a discussion of why zerocopy for vmalloc data is not a good idea.

Discovered while testing NBD traffic encrypted with ktls.

Fixes: c46234eb ("tls: RX path for ktls")
Signed-off-by: Doron Roberts-Kedes <doronrk@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tls/tls_sw.c

@@ -362,6 +362,7 @@ int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 	int record_room;
 	bool full_record;
 	int orig_size;
+	bool is_kvec = msg->msg_iter.type & ITER_KVEC;
 
 	if (msg->msg_flags & ~(MSG_MORE | MSG_DONTWAIT | MSG_NOSIGNAL))
 		return -ENOTSUPP;
@@ -410,8 +411,7 @@ int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 			try_to_copy -= required_size - ctx->sg_encrypted_size;
 			full_record = true;
 		}
-
-		if (full_record || eor) {
+		if (!is_kvec && (full_record || eor)) {
 			ret = zerocopy_from_iter(sk, &msg->msg_iter,
 				try_to_copy, &ctx->sg_plaintext_num_elem,
 				&ctx->sg_plaintext_size,
@@ -779,6 +779,7 @@ int tls_sw_recvmsg(struct sock *sk,
 	bool cmsg = false;
 	int target, err = 0;
 	long timeo;
+	bool is_kvec = msg->msg_iter.type & ITER_KVEC;
 
 	flags |= nonblock;
 
@@ -822,7 +823,7 @@ int tls_sw_recvmsg(struct sock *sk,
 			page_count = iov_iter_npages(&msg->msg_iter,
 						     MAX_SKB_FRAGS);
 			to_copy = rxm->full_len - tls_ctx->rx.overhead_size;
-			if (to_copy <= len && page_count < MAX_SKB_FRAGS &&
+			if (!is_kvec && to_copy <= len && page_count < MAX_SKB_FRAGS &&
 			    likely(!(flags & MSG_PEEK)))  {
 				struct scatterlist sgin[MAX_SKB_FRAGS + 1];
 				int pages = 0;