Re: Re: [PATCH] net: fix null pointer dereference when parsing ICMP6_ROUTER_ADVERTISE messages

[zhangqiumiao]

On Thu, Feb 17, 2022 at 03:32:52PM -0600, Glenn Washburn wrote:
> On Thu, 17 Feb 2022 21:48:58 +0800
> Qiumiao Zhang via Grub-devel <grub-devel@gnu.org> wrote:
>
> > During UEFI PXE boot in IPv6 network, if the DHCP server adopts 
> > stateful automatic configuration, when the client receives the 
> > ICMP6_ROUTER_ADVERTISE message multicast from the server, it will 
> > cause the problem of dereference null pointer and cause the grub2 program 
> > to crash.
>
> This commit message could be more clear. Maybe have something like:
>
>   During UEFI PXE boot in IPv6 network, if the DHCP server adopts
>   stateful automatic configuration, then the client receives a
>   ICMP6_ROUTER_ADVERTISE multicast message from the server. This may be
>   received without the interfaced having a configured network address,
>   so orig_inf will be null, which can lead to a null dereference when
>   creating the default route.
>

Yes, that's a better description.

> Of course, assuming that the above is in fact correct.
>
> >
> > Fixes bug: https://savannah.gnu.org/bugs/index.php?62072
> > ---
> >  grub-core/net/icmp6.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/grub-core/net/icmp6.c b/grub-core/net/icmp6.c index 
> > 2cbd95d..264fc4a 100644
> > --- a/grub-core/net/icmp6.c
> > +++ b/grub-core/net/icmp6.c
> > @@ -477,7 +477,7 @@ grub_net_recv_icmp6_packet (struct grub_net_buff 
> > *nb,
> >
> >         /* May not have gotten slaac info, find a global address on this
> >           card.  */
> > -       if (route_inf == NULL)
> > +       if (route_inf == NULL && orig_inf != NULL)
>
> So if orig_inf == NULL and route_inf == NULL here, we do not set a 
> default route. Does this have any implications to be concerned about?
>
> In this case, can we still find a good route interface and setup a 
> default route?

If the DHCP server adopts stateful automatic configuration, the client obtains 
the default route through DHCPv6 instead of RA messages. So if orig_inf == NULL 
and route_inf == null, we should not set the default route.

Qiumiao