Subject: [PATCH net 3/5] ipv6: Check attribute length for RTA_GATEWAY in multipath route

From: David Ahern <[email-masked]>
Date: Thu, 30 Dec 2021 17:36:33 -0700

Commit referenced in the Fixes tag used nla_memcpy for RTA_GATEWAY as
does the current nla_get_in6_addr. nla_memcpy protects against accessing
memory greater than what is in the attribute, but there is no check
requiring the attribute to have an IPv6 address. Add it.

Fixes: 51ebd3181572 ("ipv6: add support of equal cost multipath (ECMP)")
Signed-off-by: David Ahern <[email-masked]>
Cc: Nicolas Dichtel <[email-masked]>
---
 net/ipv6/route.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 42d60c76d30a..d16599c225b8 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -5224,6 +5224,19 @@ static bool ip6_route_mpath_should_notify(const struct fib6_info *rt)
 	return should_notify;
 }
 
+static int fib6_gw_from_attr(struct in6_addr *gw, struct nlattr *nla,
+			     struct netlink_ext_ack *extack)
+{
+	if (nla_len(nla) < sizeof(*gw)) {
+		NL_SET_ERR_MSG(extack, "Invalid IPv6 address in RTA_GATEWAY");
+		return -EINVAL;
+	}
+
+	*gw = nla_get_in6_addr(nla);
+
+	return 0;
+}
+
 static int ip6_route_multipath_add(struct fib6_config *cfg,
 				   struct netlink_ext_ack *extack)
 {
@@ -5264,7 +5277,13 @@ static int ip6_route_multipath_add(struct fib6_config *cfg,
 
 			nla = nla_find(attrs, attrlen, RTA_GATEWAY);
 			if (nla) {
-				r_cfg.fc_gateway = nla_get_in6_addr(nla);
+				int ret;
+
+				ret = fib6_gw_from_attr(&r_cfg.fc_gateway, nla,
+							extack);
+				if (ret)
+					return ret;
+
 				r_cfg.fc_flags |= RTF_GATEWAY;
 			}
 			r_cfg.fc_encap = nla_find(attrs, attrlen, RTA_ENCAP);
-- 
2.24.3 (Apple Git-128)