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?
Nikolay Aleksandrov
2020-Jul-05 20:18 UTC
[Bridge] [PATCH net] bridge: mcast: Fix MLD2 Report IPv6 payload length check
On 7/5/20 10:49 PM, Linus L?ssing wrote:> 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? >Sure, I just thought the ipv6_mc_may_pull() call after that includes those 2 bytes as well, so we're covered. That is, it seems to be doing the same check with the full grec size included.