[PATCH net-next v2 5/5] bridge: Use ndisc_parse_options() to parse ND options in br_nd_send()

[Danielle Ratson <danieller@nvidia.com>]

Replace the manual ND option parsing loop in br_nd_send() with
ndisc_parse_options(), which provides proper validation and avoids the
class of bugs that were fixed by commit 53fc685243bd ("bridge: Avoid
infinite loop when suppressing NS messages with invalid options") and
commit 850837965af1 ("bridge: br_nd_send: validate ND option lengths").

Use ndisc_opt_addr_data() to extract the source link-layer address
from the parsed options, which correctly validates the option length
for the underlying device type.

Export ndisc_parse_options() so that it can be resolved from the bridge
when it is built as a module (CONFIG_BRIDGE=m); otherwise modpost fails
with an undefined symbol.

Reviewed-by: Petr Machata <petrm@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Danielle Ratson <danieller@nvidia.com>
---

Notes:
    v2:
    	* Use EXPORT_SYMBOL_GPL() instead of EXPORT_SYMBOL() to export
    	  ndisc_parse_options().

 net/bridge/br_arp_nd_proxy.c | 32 +++++++++++++++++---------------
 net/ipv6/ndisc.c             |  1 +
 2 files changed, 18 insertions(+), 15 deletions(-)

diff --git a/net/bridge/br_arp_nd_proxy.c b/net/bridge/br_arp_nd_proxy.c
index 6b6de0eff38c..b6e5a86b6a92 100644
--- a/net/bridge/br_arp_nd_proxy.c
+++ b/net/bridge/br_arp_nd_proxy.c
@@ -255,15 +255,16 @@ static void br_nd_send(struct net_bridge *br, struct net_bridge_port *p,
 {
 	struct net_device *dev = request->dev;
 	struct net_bridge_vlan_group *vg;
+	struct ndisc_options ndopts;
 	struct nd_msg *na, *ns;
 	struct sk_buff *reply;
 	struct ipv6hdr *pip6;
 	int na_olen = 8; /* opt hdr + ETH_ALEN for target */
 	int ns_olen;
-	int i, len;
 	u8 *daddr;
 	bool dad;
 	u16 pvid;
+	int len;
 
 	if (!dev)
 		return;
@@ -284,20 +285,21 @@ static void br_nd_send(struct net_bridge *br, struct net_bridge_port *p,
 	daddr = eth_hdr(request)->h_source;
 	ns = (struct nd_msg *)skb_transport_header(request);
 
-	/* Do we need option processing ? */
-	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] || i + (ns->opt[i + 1] << 3) > ns_olen) {
-			kfree_skb(reply);
-			return;
-		}
-		if (ns->opt[i] == ND_OPT_SOURCE_LL_ADDR) {
-			if ((ns->opt[i + 1] << 3) >=
-			    sizeof(struct nd_opt_hdr) + ETH_ALEN)
-				daddr = ns->opt + i + sizeof(struct nd_opt_hdr);
-			break;
-		}
+	/* Derive the option length from the IPv6 payload length so that any
+	 * trailing L2 padding in the skb is not parsed as ND options.
+	 */
+	ns_olen = ntohs(ipv6_hdr(request)->payload_len) - sizeof(*ns);
+	if (!ndisc_parse_options(dev, ns->opt, ns_olen, &ndopts)) {
+		kfree_skb(reply);
+		return;
+	}
+
+	if (ndopts.nd_opts_src_lladdr) {
+		u8 *lladdr;
+
+		lladdr = ndisc_opt_addr_data(ndopts.nd_opts_src_lladdr, dev);
+		if (lladdr)
+			daddr = lladdr;
 	}
 
 	dad = ipv6_addr_any(&ipv6_hdr(request)->saddr);
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index fe36b3f51285..2ceb655c4229 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -283,6 +283,7 @@ struct ndisc_options *ndisc_parse_options(const struct net_device *dev,
 	}
 	return ndopts;
 }
+EXPORT_SYMBOL_GPL(ndisc_parse_options);
 
 int ndisc_mc_map(const struct in6_addr *addr, char *buf, struct net_device *dev, int dir)
 {
-- 
2.54.0