Linux Ethernet Bridging - Jul 2020 - [Bridge] [PATCH net] bridge: mcast: Fix MLD2 Report IPv6 payload length check

On Sun, Jul 05, 2020 at 09:33:13PM +0300, Nikolay Aleksandrov
wrote:
> On 05/07/2020 21:22, Linus L?ssing 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 L?ssing <linus.luessing at c0d3.blue>
> > ---
> >  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 at cumulusnetworks.com>
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.

On 7/5/20 10:08 PM, Linus L?ssing wrote:
> On Sun, Jul 05, 2020 at 09:33:13PM +0300, Nikolay Aleksandrov wrote:
>> On 05/07/2020 21:22, Linus L?ssing 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 L?ssing <linus.luessing at c0d3.blue>
>>> ---
>>>   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 at cumulusnetworks.com>
> 
> 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.