Re: [PATCH net] bridge: mcast: Fix MLD2 Report IPv6 payload length check

[Nikolay Aleksandrov]

On 7/5/20 10:08 PM, Linus LÃssing wrote:
> On Sun, Jul 05, 2020 at 09:33:13PM +0300, Nikolay Aleksandrov wrote:
> > On 05/07/2020 21:22, Linus LÃssing wrote:
> > > Commit e57f61858b7c ("net: bridge: mcast: fix stale nsrcs pointer in
> > > igmp3/mld2 report handling") introduced a small bug which would potentially
> > > lead to accepting an MLD2 Report with a broken IPv6 header payload length
> > > field.
> > >
> > > The check needs to take into account the 2 bytes for the "Number of
> > > Sources" field in the "Multicast Address Record" before reading it.
> > > And not the size of a pointer to this field.
> > >
> > > Fixes: e57f61858b7c ("net: bridge: mcast: fix stale nsrcs pointer in igmp3/mld2 report handling")
> > > Signed-off-by: Linus LÃssing <linus.luessing@xxxxxxxxx>
> > > ---
> > >   net/bridge/br_multicast.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > I'd rather be more concerned with it rejecting a valid report due to wrong size. The ptr
> > size would always be bigger. :)
> >
> > Thanks!
> > Acked-by: Nikolay Aleksandrov <nikolay@xxxxxxxxxxxxxxxxxxx>
>
> Aiy, you're right, it's the other way round. I'll update the
> commit message and send a v2 in a minute, with your Acked-by
> included.

By the way, I can't verify at the moment, but I think we can drop that whole
hunk altogether since skb_header_pointer() is used and it will simply return
an error if there isn't enough data for nsrcs.