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

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Fri, Mar 26, 2021 at 1:14 PM Song Liu <song@kernel.org> wrote:
>
> On Fri, Mar 26, 2021 at 9:07 AM Lorenz Bauer <lmb@cloudflare.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@cloudflare.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?

Map does use f_flags, so we need to let them through. Or did you mean
to do a (type != BPF_TYPE_MAP && f_flags != O_RDWR) check?

Either way is fine with me, so:

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

>
> 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
> >