netdev - Re: [PATCH 2/2] bpf: cgroup: Fix problematic bounds check

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Message-ID: <CAKH8qBtOVr_y2r2dSC+p7E1jfehXsh-RUdNLeo3n7zquMzogBw@mail.gmail.com>
Date:   Fri, 22 Jan 2021 09:04:54 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Loris Reiff <loris.reiff@...lor.ch>
Cc:     bpf <bpf@...r.kernel.org>, Netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>, kpsingh@...nel.org
Subject: Re: [PATCH 2/2] bpf: cgroup: Fix problematic bounds check

On Fri, Jan 22, 2021 at 8:43 AM Loris Reiff <loris.reiff@...lor.ch> wrote:
>
> Since ctx.optlen is signed, a larger value than max_value could be
> passed, as it is later on used as unsigned, which causes a WARN_ON_ONCE
> in the copy_to_user.
>
> Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks")
> Signed-off-by: Loris Reiff <loris.reiff@...lor.ch>
> ---
>  kernel/bpf/cgroup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index 6ec8f02f4..6aa9e10c6 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -1464,7 +1464,7 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level,
>                 goto out;
>         }
>
> -       if (ctx.optlen > max_optlen) {
> +       if (ctx.optlen > max_optlen || ctx.optlen < 0) {
>                 ret = -EFAULT;
>                 goto out;
>         }
> --
> 2.29.2
Thanks! I assume this is only an issue if the BPF program is written
incorrectly.

Reviewed-by: Stanislav Fomichev <sdf@...gle.com>