ipv6: Check attribute length for RTA_GATEWAY when deleting multipath route

stable inclusion
from stable-v5.10.91
commit 48d5adb08d60116e9d05f01dcdbe698b5d54cdbb
bugzilla: 186187 https://gitee.com/openeuler/kernel/issues/I4SI2C

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=48d5adb08d60116e9d05f01dcdbe698b5d54cdbb

--------------------------------

commit 1ff15a71 upstream.

Make sure RTA_GATEWAY for IPv6 multipath route has enough bytes to hold
an IPv6 address.

Fixes: 6b9ea5a6 ("ipv6: fix multipath route replace error recovery")
Signed-off-by: NDavid Ahern <dsahern@kernel.org>
Cc: Roopa Prabhu <roopa@nvidia.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

net/ipv6/route.c

@@ -5342,7 +5342,11 @@ static int ip6_route_multipath_del(struct fib6_config *cfg,
 
 			nla = nla_find(attrs, attrlen, RTA_GATEWAY);
 			if (nla) {
-				nla_memcpy(&r_cfg.fc_gateway, nla, 16);
+				err = fib6_gw_from_attr(&r_cfg.fc_gateway, nla,
+							extack);
+				if (err)
+					return err;
+
 				r_cfg.fc_flags |= RTF_GATEWAY;
 			}
 		}