netdev - Re: [PATCH bpf-next 04/16] net: Add BPF_XDP_EGRESS as a bpf_attach

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Date:   Thu, 23 Apr 2020 18:58:12 -0600
From:   David Ahern <dsahern@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     David Ahern <dsahern@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Prashant Bhole <prashantbhole.linux@...il.com>,
        Jason Wang <jasowang@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toshiaki Makita <toshiaki.makita1@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        David Ahern <dahern@...italocean.com>
Subject: Re: [PATCH bpf-next 04/16] net: Add BPF_XDP_EGRESS as a
 bpf_attach_type

On 4/23/20 6:53 PM, Alexei Starovoitov wrote:
> 
> I think the issue is not related to xdp egress.

It isn't; that has been my point all along.

> Hence I'd like to push the fix along with selftest into bpf tree.
> The selftest can be:
> void noinline do_bind((struct bpf_sock_addr *ctx)
> {
>   struct sockaddr_in sa = {};
> 
>   bpf_bind(ctx, (struct sockaddr *)&sa, sizeof(sa));
>   return 0;
> }
> SEC("cgroup/connect4")
> int connect_v4_prog(struct bpf_sock_addr *ctx)
> {
>   return do_bind(ctx);
> }
> 
> and freplace would replace do_bind() with do_new_bind()
> that also calls bpf_bind().
> I think without the fix freplace will fail to load, because
> availability of bpf_bind() depends on correct prog->expected_attach_type.
> 
> I haven't looked at the crash you mentioned in the other email related
> to xdp egress set. That could be different issue. I hope it's the same thing :)
> 

it is. The replaced program is accessing ingress_ifindex from xdp egress
context, and Rx stuff is not set (access is blocked by verifier).