[PATCH net-next] tls: Skip zerocopy path for ITER_KVEC

[Doron Roberts-Kedes <doronrk@fb.com>]

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: c46234ebb4d1 ("tls: RX path for ktls")
Signed-off-by: Doron Roberts-Kedes <doronrk@fb.com>
---
 net/tls/tls_sw.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index 4618f1c31137..ef15e35232dd 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -426,7 +426,8 @@ int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 			full_record = true;
 		}
 
-		if (full_record || eor) {
+		bool iskvec = msg->msg_iter.type & ITER_KVEC;
+		if (!iskvec && (full_record || eor)) {
 			ret = zerocopy_from_iter(sk, &msg->msg_iter,
 				try_to_copy, &ctx->sg_plaintext_num_elem,
 				&ctx->sg_plaintext_size,
@@ -804,7 +805,8 @@ 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 &&
+			bool iskvec = msg->msg_iter.type & ITER_KVEC;
+			if (!iskvec && to_copy <= len && page_count < MAX_SKB_FRAGS &&
 			    likely(!(flags & MSG_PEEK)))  {
 				struct scatterlist sgin[MAX_SKB_FRAGS + 1];
 				int pages = 0;
-- 
2.17.1