tcp: really ignore MSG_ZEROCOPY if no SO_ZEROCOPY

BugLink: https://bugs.launchpad.net/bugs/1836117
[ 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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 27288fbdf1b621bbcb04664a0e1c05bb7ebccbfb..c43188d10409bd3abe96775c231a08077d2eaf2e 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -937,9 +937,6 @@ 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;

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 96d22014b16bfbfc36b0727a3c599df26582af95..11c7550c1df0f43d45fa0d2cea66e019e81956a1 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1193,7 +1193,7 @@ 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;