Subject: [PATCH 05/12] bridge: Avoid infinite loop when suppressing NS messages with invalid options

From: Ido Schimmel <[email-masked]>
Date: Mon, 1 Jun 2020 15:58:54 +0300

[ Upstream commit 53fc685243bd6fb90d90305cea54598b78d3cbfc ]

When neighbor suppression is enabled the bridge device might reply to
Neighbor Solicitation (NS) messages on behalf of remote hosts.

In case the NS message includes the "Source link-layer address" option
[1], the bridge device will use the specified address as the link-layer
destination address in its reply.

To avoid an infinite loop, break out of the options parsing loop when
encountering an option with length zero and disregard the NS message.

This is consistent with the IPv6 ndisc code and RFC 4886 which states
that "Nodes MUST silently discard an ND packet that contains an option
with length zero" [2].

[1] https://tools.ietf.org/html/rfc4861#section-4.3
[2] https://tools.ietf.org/html/rfc4861#section-4.6

Fixes: ed842faeb2bd ("bridge: suppress nd pkts on BR_NEIGH_SUPPRESS ports")
Signed-off-by: Ido Schimmel <[email-masked]>
Reported-by: Alla Segal <[email-masked]>
Tested-by: Alla Segal <[email-masked]>
Acked-by: Nikolay Aleksandrov <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/bridge/br_arp_nd_proxy.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/bridge/br_arp_nd_proxy.c b/net/bridge/br_arp_nd_proxy.c
index 37908561a64b..b18cdf03edb3 100644
--- a/net/bridge/br_arp_nd_proxy.c
+++ b/net/bridge/br_arp_nd_proxy.c
@@ -276,6 +276,10 @@ static void br_nd_send(struct net_bridge *br, struct net_bridge_port *p,
 	ns_olen = request->len - (skb_network_offset(request) +
 				  sizeof(struct ipv6hdr)) - sizeof(*ns);
 	for (i = 0; i < ns_olen - 1; i += (ns->opt[i + 1] << 3)) {
+		if (!ns->opt[i + 1]) {
+			kfree_skb(reply);
+			return;
+		}
 		if (ns->opt[i] == ND_OPT_SOURCE_LL_ADDR) {
 			daddr = ns->opt + i + sizeof(struct nd_opt_hdr);
 			break;
-- 
2.26.2