Nikolay Aleksandrov
2020-Jul-05 19:11 UTC
[Bridge] [PATCH net] bridge: mcast: Fix MLD2 Report IPv6 payload length check
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.
Linus Lüssing
2020-Jul-05 19:49 UTC
[Bridge] [PATCH net] bridge: mcast: Fix MLD2 Report IPv6 payload length check
On Sun, Jul 05, 2020 at 10:11:39PM +0300, Nikolay Aleksandrov wrote:> 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. >Hm, while unlikely, the IPv6 packet / header payload length might be shorter than the frame / skb size. And even though it wouldn't crash reading over the IPv6 packet length, especially as skb_header_pointer() is used, I think we should still avoid reading over the size indicated by the IPv6 header payload length field, to stay protocol compliant. Does that make sense?