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

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Date:   Mon, 29 Mar 2021 09:19:13 +0100
From:   Lorenz Bauer <lmb@...udflare.com>
To:     Song Liu <song@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        kernel-team <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, 26 Mar 2021 at 20:14, Song Liu <song@...nel.org> wrote:
>
> 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?

type is filled in by bpf_obj_do_get, so we can't avoid calling it. As
Andrii mentions we need to allow flags for map.

>
> 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
> >



-- 
Lorenz Bauer  |  Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK

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