netdev - Re: [PATCH bpf] bpf: fix potential race in tail call compatibility check

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAADnVQLPBLc0T32nqM7Q_LBEGWiJRp3JvGaY2Lsmf9yqJW+Yfw@mail.gmail.com>
Date:   Thu, 21 Oct 2021 17:48:18 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Subject: Re: [PATCH bpf] bpf: fix potential race in tail call compatibility check

On Thu, Oct 21, 2021 at 11:40 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
> +       map_type = READ_ONCE(array->aux->type);
> +       if (!map_type) {
> +               /* There's no owner yet where we could check for compatibility.
> +                * Do an atomic swap to prevent racing with another invocation
> +                * of this branch (via simultaneous map_update syscalls).
>                  */
> -               array->aux->type  = fp->type;
> -               array->aux->jited = fp->jited;
> +               if (cmpxchg(&array->aux->type, 0, prog_type))
> +                       return false;

Other fields might be used in the compatibility check in the future.
This hack is too fragile.
Just use a spin_lock.