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Subject[PATCH 4.18 012/235] tcp: really ignore MSG_ZEROCOPY if no SO_ZEROCOPY
Date
4.18-stable review patch.  If anyone has any objections, please let me know.

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

From: Vincent Whitchurch <vincent.whitchurch@axis.com>

[ 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@axis.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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
@@ -939,9 +939,6 @@ 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
@@ -1186,7 +1186,7 @@ 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;

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