netdev - Re: [net] tcp: Specify cmsgbuf is user pointer for receive zerocopy.

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Date:   Thu, 6 May 2021 12:00:08 -0700
From:   Arjun Roy <arjunroy@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Arjun Roy <arjunroy.kdev@...il.com>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: [net] tcp: Specify cmsgbuf is user pointer for receive zerocopy.

On Thu, May 6, 2021 at 11:56 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Thu, May 6, 2021 at 8:43 PM Arjun Roy <arjunroy.kdev@...il.com> wrote:
> >
> > From: Arjun Roy <arjunroy@...gle.com>
> >
> > A prior change introduces separate handling for ->msg_control
> > depending on whether the pointer is a kernel or user pointer. However,
> > it does not update tcp receive zerocopy (which uses a user pointer),
> > which can cause faults when the improper mechanism is used.
> >
> > This patch simply annotates tcp receive zerocopy's use as explicitly
> > being a user pointer.
> >
> > Fixes: 1f466e1f15cf ("net: cleanly handle kernel vs user buffers for ->msg_control")
>
> This Fixes: tag is wrong.
>
> When this commit was merged, tcp_zc_finalize_rx_tstamp() was not yet there.
>

Makes sense - I'll send out an amended v2 patch that tags
'7eeba1706eba' instead.

-Arjun

> > Signed-off-by: Arjun Roy <arjunroy@...gle.com>
> > ---
> >  net/ipv4/tcp.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> > index e14fd0c50c10..f1c1f9e3de72 100644
> > --- a/net/ipv4/tcp.c
> > +++ b/net/ipv4/tcp.c
> > @@ -2039,6 +2039,7 @@ static void tcp_zc_finalize_rx_tstamp(struct sock *sk,
> >                 (__kernel_size_t)zc->msg_controllen;
> >         cmsg_dummy.msg_flags = in_compat_syscall()
> >                 ? MSG_CMSG_COMPAT : 0;
> > +       cmsg_dummy.msg_control_is_user = true;
> >         zc->msg_flags = 0;
> >         if (zc->msg_control == msg_control_addr &&
> >             zc->msg_controllen == cmsg_dummy.msg_controllen) {
> > --
> > 2.31.1.607.g51e8a6a459-goog
> >