Commit 5cf4a853 authored Sep 06, 2018 by Vincent Whitchurch Committed by David S. Miller Sep 07, 2018

tcp: really ignore MSG_ZEROCOPY if no SO_ZEROCOPY



According to the documentation in msg_zerocopy.rst, the SO_ZEROCOPY
flag was introduced because send(2) ignores unknown message flags and
any legacy application which was accidentally passing the equivalent of
MSG_ZEROCOPY earlier should not see any new behaviour.

Before commit f214f915 ("tcp: enable MSG_ZEROCOPY"), a send(2) call
which passed the equivalent of MSG_ZEROCOPY without setting SO_ZEROCOPY
would succeed.  However, after that commit, it fails with -ENOBUFS.  So
it appears that the SO_ZEROCOPY flag fails to fulfill its intended
purpose.  Fix it.

Fixes: f214f915 ("tcp: enable MSG_ZEROCOPY")
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent a162c351

net/core/skbuff.c

+0 −3

Original line number	Diff line number	Diff line
		@@ -939,9 +939,6 @@ struct ubuf_info sock_zerocopy_alloc(struct sock sk, size_t size)

		WARN_ON_ONCE(!in_task());

		if (!sock_flag(sk, SOCK_ZEROCOPY))
		return NULL;

		skb = sock_omalloc(sk, 0, GFP_KERNEL);
		if (!skb)
		return NULL;

net/ipv4/tcp.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1185,7 +1185,7 @@ int tcp_sendmsg_locked(struct sock sk, struct msghdr msg, size_t size)

		flags = msg->msg_flags;

		if (flags & MSG_ZEROCOPY && size) {
		if (flags & MSG_ZEROCOPY && size && sock_flag(sk, SOCK_ZEROCOPY)) {
		if (sk->sk_state != TCP_ESTABLISHED) {
		err = -EINVAL;
		goto out_err;