FAILED: patch "[PATCH] ipv6: Check attribute length for RTA_GATEWAY in multipath" failed to apply to 4.9-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 4619bcf91399f00a40885100fb61d594d8454033 Mon Sep 17 00:00:00 2001
From: David Ahern <dsahern@kernel.org>
Date: Thu, 30 Dec 2021 17:36:33 -0700
Subject: [PATCH] ipv6: Check attribute length for RTA_GATEWAY in multipath
 route

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 <dsahern@kernel.org>
Cc: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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);