Re: linux-next: manual merge of the net-next tree with the net tree

[Daniel Borkmann]

On 3/19/21 3:11 AM, Piotr Krysiuk wrote:
> Hi Daniel,
>
> On Fri, Mar 19, 2021 at 12:16 AM Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
> wrote:
>
> > diff --cc kernel/bpf/verifier.c
> > index 44e4ec1640f1,f9096b049cd6..000000000000
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@@ -5876,10 -6056,22 +6060,23 @@@ static int retrieve_ptr_limit(const str
> >                  if (mask_to_left)
> >                          *ptr_limit = MAX_BPF_STACK + off;
> >                  else
> >   -                      *ptr_limit = -off;
> >   -              return 0;
> >   +                      *ptr_limit = -off - 1;
> >   +              return *ptr_limit >= max ? -ERANGE : 0;
> > +       case PTR_TO_MAP_KEY:
> > +               /* Currently, this code is not exercised as the only use
> > +                * is bpf_for_each_map_elem() helper which requires
> > +                * bpf_capble. The code has been tested manually for
> > +                * future use.
> > +                */
> > +               if (mask_to_left) {
> > +                       *ptr_limit = ptr_reg->umax_value + ptr_reg->off;
> > +               } else {
> > +                       off = ptr_reg->smin_value + ptr_reg->off;
> > +                       *ptr_limit = ptr_reg->map_ptr->key_size - off;
> > +               }
> > +               return 0;
>
> PTR_TO_MAP_VALUE logic above looks like copy-paste of old PTR_TO_MAP_VALUE
> code from before "bpf: Fix off-by-one for area size in creating mask to
> left" and is apparently affected by the same off-by-one, except this time
> on "key_size" area and not "value_size".
>
> This needs to be fixed in the same way as we did with PTR_TO_MAP_VALUE.
> What is the best way to proceed?

Hm, not sure why PTR_TO_MAP_KEY was added by 69c087ba6225 in the first place, I
presume noone expects this to be used from unprivileged as the comment says.
Resolution should be to remove the PTR_TO_MAP_KEY case entirely from that switch
until we have an actual user.

Thanks,
Daniel