Linux Ethernet Bridging - Jul 2020 - [Bridge] [PATCH net v2] bridge: mcast: Fix MLD2 Report IPv6 payload length check

Commit e57f61858b7c ("net: bridge: mcast: fix stale nsrcs pointer in
igmp3/mld2 report handling") introduced a bug in the IPv6 header payload
length check which would potentially lead to rejecting a valid MLD2 Report:

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")
Acked-by: Nikolay Aleksandrov <nikolay at cumulusnetworks.com>
Signed-off-by: Linus L?ssing <linus.luessing at c0d3.blue>
---
Changelog v2:
* updated commit message, the issue is accidentally rejcting a valid and
  not accepting an invalid MLD2 Report

 net/bridge/br_multicast.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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);
 
-- 
2.27.0

From: Linus L?ssing <linus.luessing at c0d3.blue>
Date: Sun,  5 Jul 2020 21:10:17 +0200
> Commit e57f61858b7c ("net: bridge: mcast: fix stale nsrcs pointer in
> igmp3/mld2 report handling") introduced a bug in the IPv6 header
payload
> length check which would potentially lead to rejecting a valid MLD2 Report:
> 
> 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")
> Acked-by: Nikolay Aleksandrov <nikolay at cumulusnetworks.com>
> Signed-off-by: Linus L?ssing <linus.luessing at c0d3.blue>
Applied and queued up for -stable, thank you.