[PATCH 5.4 005/215] bridge: mcast: Fix MLD2 Report IPv6 payload length check

[Greg Kroah-Hartman]

From: "Linus Lü" <linus.luessing@xxxxxxxxx>

[ Upstream commit 5fc6266af7b427243da24f3443a50cd4584aac06 ]

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@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus LÃssing <linus.luessing@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/bridge/br_multicast.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1007,7 +1007,7 @@ static int br_ip6_multicast_mld2_report(
 		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,