netdev - Re: [PATCH bpf v2 2/2] bpf: program: refuse non-O_RDWR flags in BPF_OBJ

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Date:   Fri, 26 Mar 2021 13:13:46 -0700
From:   Song Liu <song@...nel.org>
To:     Lorenz Bauer <lmb@...udflare.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        kernel-team@...udflare.com, Networking <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf v2 2/2] bpf: program: refuse non-O_RDWR flags in BPF_OBJ_GET

On Fri, Mar 26, 2021 at 9:07 AM Lorenz Bauer <lmb@...udflare.com> wrote:
>
> As for bpf_link, refuse creating a non-O_RDWR fd. Since program fds
> currently don't allow modifications this is a precaution, not a
> straight up bug fix.
>
> Signed-off-by: Lorenz Bauer <lmb@...udflare.com>
> ---
>  kernel/bpf/inode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
> index dc56237d6960..d2de2abec35b 100644
> --- a/kernel/bpf/inode.c
> +++ b/kernel/bpf/inode.c
> @@ -543,7 +543,7 @@ int bpf_obj_get_user(const char __user *pathname, int flags)
>                 return PTR_ERR(raw);

For both patches, shall we do the check before bpf_obj_do_get(), which is a few
lines above?

Thanks,
Song

>
>         if (type == BPF_TYPE_PROG)
> -               ret = bpf_prog_new_fd(raw);
> +               ret = (f_flags != O_RDWR) ? -EINVAL : bpf_prog_new_fd(raw);
>         else if (type == BPF_TYPE_MAP)
>                 ret = bpf_map_new_fd(raw, f_flags);
>         else if (type == BPF_TYPE_LINK)
> --
> 2.27.0
>