On 05/07/2020 21:22, Linus Lüssing 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 Lüssing <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>
> diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
> index 83490bf73a13..4c4a93abde68 100644
> --- a/net/bridge/br_multicast.c
> +++ b/net/bridge/br_multicast.c
> @@ -1000,21 +1000,21 @@ static int br_ip6_multicast_mld2_report(struct net_bridge *br,
> num = ntohs(icmp6h->icmp6_dataun.un_data16[1]);
> len = skb_transport_offset(skb) + sizeof(*icmp6h);
>
> for (i = 0; i < num; i++) {
> __be16 *_nsrcs, __nsrcs;
> u16 nsrcs;
>
> nsrcs_offset = len + offsetof(struct mld2_grec, grec_nsrcs);
>
> if (skb_transport_offset(skb) + ipv6_transport_len(skb) <
> - nsrcs_offset + sizeof(_nsrcs))
> + nsrcs_offset + sizeof(__nsrcs))
> return -EINVAL;
>
> _nsrcs = skb_header_pointer(skb, nsrcs_offset,
> sizeof(__nsrcs), &__nsrcs);
> if (!_nsrcs)
> return -EINVAL;
>
> nsrcs = ntohs(*_nsrcs);
> grec_len = struct_size(grec, grec_src, nsrcs);
>
>
