netdev - Re: [PATCH net-next] tcp: take care of SYN_RECV sockets in tcp_v4_send_ack() and tcp_v6_send

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Date:   Mon, 10 Jun 2019 15:34:10 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jonathan Maxwell <jmaxwell37@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next] tcp: take care of SYN_RECV sockets in
 tcp_v4_send_ack() and tcp_v6_send_response()

On Mon, Jun 10, 2019 at 3:27 PM Jonathan Maxwell <jmaxwell37@...il.com> wrote:
>
> Thanks for fixing that Eric.

Hi Jonathan.

There is no bug actually, at least not on sk->sk_mark part.

I will send a simpler patch so that sock_net_uid() correctly fetches
sk->sk_uid for FASTOPEN socket.

Thanks !



>
> On Tue, Jun 11, 2019 at 7:45 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > TCP can send ACK packets on behalf of SYN_RECV sockets.
> >
> > tcp_v4_send_ack() and tcp_v6_send_response() incorrectly
> > dereference sk->sk_mark for non TIME_WAIT sockets.
> >
> > This field is not defined for SYN_RECV sockets.
> >
> > Using sk_to_full_sk() should get back to the listener socket.
> >
> > Note that this also provides a socket pointer to sock_net_uid() calls.
> >
> > Fixes: 00483690552c ("tcp: Add mark for TIMEWAIT sockets")
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Cc: Jon Maxwell <jmaxwell37@...il.com>
> > ---
> >  net/ipv4/tcp_ipv4.c | 6 ++++--
> >  net/ipv6/tcp_ipv6.c | 1 +
> >  2 files changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> > index f059fbd81a84314ae6fef37f600b0cf28bd2ad30..2bb27d5eae78efdff52a741904d7526a234595d8 100644
> > --- a/net/ipv4/tcp_ipv4.c
> > +++ b/net/ipv4/tcp_ipv4.c
> > @@ -856,12 +856,14 @@ static void tcp_v4_send_ack(const struct sock *sk,
> >         if (oif)
> >                 arg.bound_dev_if = oif;
> >         arg.tos = tos;
> > -       arg.uid = sock_net_uid(net, sk_fullsock(sk) ? sk : NULL);
> >         local_bh_disable();
> >         ctl_sk = this_cpu_read(*net->ipv4.tcp_sk);
> > -       if (sk)
> > +       if (sk) {
> > +               sk = sk_to_full_sk(sk);
> >                 ctl_sk->sk_mark = (sk->sk_state == TCP_TIME_WAIT) ?
> >                                    inet_twsk(sk)->tw_mark : sk->sk_mark;
> > +       }
> > +       arg.uid = sock_net_uid(net, sk_fullsock(sk) ? sk : NULL);
> >         ip_send_unicast_reply(ctl_sk,
> >                               skb, &TCP_SKB_CB(skb)->header.h4.opt,
> >                               ip_hdr(skb)->saddr, ip_hdr(skb)->daddr,
> > diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> > index ad7039137a20f9ad8581d9ca01347c67aa8a8433..ea4dd988bc7f9a90e0d95283e10db5a517a59027 100644
> > --- a/net/ipv6/tcp_ipv6.c
> > +++ b/net/ipv6/tcp_ipv6.c
> > @@ -884,6 +884,7 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
> >         }
> >
> >         if (sk) {
> > +               sk = sk_to_full_sk(sk);
> >                 if (sk->sk_state == TCP_TIME_WAIT) {
> >                         mark = inet_twsk(sk)->tw_mark;
> >                         /* autoflowlabel relies on buff->hash */
> > --
> > 2.22.0.rc2.383.gf4fbbf30c2-goog
> >