netdev - Re: [PATCH bpf 1/2] xdp: check prog type before updating BPF link

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Message-ID: <87sftz8cgg.fsf@toke.dk>
Date:   Fri, 07 Jan 2022 22:26:07 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        syzbot+983941aa85af6ded1fd9@...kaller.appspotmail.com,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf 1/2] xdp: check prog type before updating BPF link

Andrii Nakryiko <andrii.nakryiko@...il.com> writes:

> On Fri, Jan 7, 2022 at 10:31 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>>
>> The bpf_xdp_link_update() function didn't check the program type before
>> updating the program, which made it possible to install any program type as
>> an XDP program, which is obviously not good. Syzbot managed to trigger this
>> by swapping in an LWT program on the XDP hook which would crash in a helper
>> call.
>>
>> Fix this by adding a check and bailing out if the types don't match.
>>
>> Fixes: 026a4c28e1db ("bpf, xdp: Implement LINK_UPDATE for BPF XDP link")
>> Reported-by: syzbot+983941aa85af6ded1fd9@...kaller.appspotmail.com
>> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
>> ---
>
> The fix looks good to me, thanks. I'd love it if this was done
> generically in link_update, but each link type has its own locking
> schema for link->prog, so I didn't figure out a way to do this in a
> centralized way.

Yeah, moving it to be a generic check was my first thought as well, but
I came to the same conclusion :)

> Acked-by: Andrii Nakryiko <andrii@...nel.org>

Thanks!

-Toke