Re: [PATCH v1 net] tcp/dccp: Don't use timer_pending() in reqsk_queue_unlink().

[Eric Dumazet <edumazet@google.com>]

On Tue, Oct 8, 2024 at 1:53 AM Kuniyuki Iwashima <kuniyu@amazon.com> wrote:
>
> From: Jakub Kicinski <kuba@kernel.org>
> Date: Mon, 7 Oct 2024 16:26:10 -0700
> > On Mon, 7 Oct 2024 07:15:57 -0700 Kuniyuki Iwashima wrote:
> > > Martin KaFai Lau reported use-after-free [0] in reqsk_timer_handler().
> > >
> > >   """
> > >   We are seeing a use-after-free from a bpf prog attached to
> > >   trace_tcp_retransmit_synack. The program passes the req->sk to the
> > >   bpf_sk_storage_get_tracing kernel helper which does check for null
> > >   before using it.
> > >   """
> >
> > I think this crashes a bunch of selftests, example:
> >
> > https://netdev-3.bots.linux.dev/vmksft-nf-dbg/results/805581/8-nft-queue-sh/stderr
>
> Oops, sorry, I copy-and-pasted __inet_csk_reqsk_queue_drop()
> for different reqsk.  I'll squash the diff below.
>
> ---8<---
> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index 36f03d51356e..433c80dc57d5 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
> @@ -1188,7 +1190,7 @@ static void reqsk_timer_handler(struct timer_list *t)
>         }
>
>  drop:
> -       __inet_csk_reqsk_queue_drop(sk_listener, nreq, true);
> +       __inet_csk_reqsk_queue_drop(sk_listener, oreq, true);
>         reqsk_put(req);
>  }
>
> ---8<---
>
> Thanks!

Just to clarify. In the old times rsk_timer was pinned, right ?

83fccfc3940c4 ("inet: fix potential deadlock in reqsk_queue_unlink()")
was fine I think.

So the bug was added recently ?

Can we give a precise Fixes: tag ?

Thank you.