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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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