netdev - Re: [PATCH bpf v4] bpf: Support dual-stack sockets in bpf_tcp_check

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Date:   Wed, 6 Apr 2022 00:18:02 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Maxim Mikityanskiy <maximmi@...dia.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Arthur Fabre <afabre@...udflare.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        linux-kselftest@...r.kernel.org, Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Tariq Toukan <tariqt@...dia.com>
Subject: Re: [PATCH bpf v4] bpf: Support dual-stack sockets in
 bpf_tcp_check_syncookie

Hey Maxim,

On 3/29/22 3:30 PM, Maxim Mikityanskiy wrote:
> bpf_tcp_gen_syncookie looks at the IP version in the IP header and
> validates the address family of the socket. It supports IPv4 packets in
> AF_INET6 dual-stack sockets.
> 
> On the other hand, bpf_tcp_check_syncookie looks only at the address
> family of the socket, ignoring the real IP version in headers, and
> validates only the packet size. This implementation has some drawbacks:
> 
> 1. Packets are not validated properly, allowing a BPF program to trick
>     bpf_tcp_check_syncookie into handling an IPv6 packet on an IPv4
>     socket.
> 
> 2. Dual-stack sockets fail the checks on IPv4 packets. IPv4 clients end
>     up receiving a SYNACK with the cookie, but the following ACK gets
>     dropped.
> 
> This patch fixes these issues by changing the checks in
> bpf_tcp_check_syncookie to match the ones in bpf_tcp_gen_syncookie. IP
> version from the header is taken into account, and it is validated
> properly with address family.
> 
> Fixes: 399040847084 ("bpf: add helper to check for a valid SYN cookie")
> Signed-off-by: Maxim Mikityanskiy <maximmi@...dia.com>
> Reviewed-by: Tariq Toukan <tariqt@...dia.com>

Could you do one final spin (while retaining Arthur's Ack) by splitting
off the selftest into a separate commit? Otherwise stable folks likely
won't be able to pick the fix up. Otherwise lgtm.

Thanks,
Daniel