[PATCH net 1/1] tcp: reject non zerocopy devmem tx

Device memory send doesn't work without zero copy, prevent
tcp_sendmsg_locked() from falling back to the copy mode for devmem in
case there is no NETIF_F_SG. Currently, it'd try to copy from iovec
filled with dma-buf offsets, which would normally fail with EFAULT, but
it's still better to handle it more explicitly. A recent net-iov / page
mixing fix also needs this patch.

Fixes: bd61848900bff ("net: devmem: Implement TX path")
Signed-off-by: Pavel Begunkov <[email protected]>
---
 net/ipv4/tcp.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 455441f1b694..f403830af65f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1162,6 +1162,10 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 					binding = NULL;
 					goto out_err;
 				}
+				if (zc != MSG_ZEROCOPY) {
+					err = -EOPNOTSUPP;
+					goto out_err;
+				}
 			}
 		}
 	} else if (unlikely(msg->msg_flags & MSG_SPLICE_PAGES) && size) {
-- 
2.54.0