[PATCH 4.14 011/173] tcp: really ignore MSG_ZEROCOPY if no SO_ZEROCOPY

From: Greg Kroah-Hartman
Date: Mon Sep 24 2018 - 08:12:21 EST


4.14-stable review patch. If anyone has any objections, please let me know.

------------------

From: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>

[ Upstream commit 5cf4a8532c992bb22a9ecd5f6d93f873f4eaccc2 ]

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 f214f915e7db ("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: f214f915e7db ("tcp: enable MSG_ZEROCOPY")
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
Acked-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/core/skbuff.c | 3 ---
net/ipv4/tcp.c | 2 +-
2 files changed, 1 insertion(+), 4 deletions(-)

--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -937,9 +937,6 @@ struct ubuf_info *sock_zerocopy_alloc(st

WARN_ON_ONCE(!in_task());

- if (!sock_flag(sk, SOCK_ZEROCOPY))
- return NULL;
-
skb = sock_omalloc(sk, 0, GFP_KERNEL);
if (!skb)
return NULL;
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1177,7 +1177,7 @@ int tcp_sendmsg_locked(struct sock *sk,

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;