netdev - [PATCH v1 net-next 04/13] ipv6: Check GATEWAY in rtm_to_fib6_multipath

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Message-ID: <20250321040131.21057-5-kuniyu@amazon.com>
Date: Thu, 20 Mar 2025 21:00:41 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, "Paolo
 Abeni" <pabeni@...hat.com>
CC: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...zon.com>,
	Kuniyuki Iwashima <kuni1840@...il.com>, <netdev@...r.kernel.org>
Subject: [PATCH v1 net-next 04/13] ipv6: Check GATEWAY in rtm_to_fib6_multipath_config().

In ip6_route_multipath_add(), we call rt6_qualify_for_ecmp() for each
entry.  If it returns false, the request fails.

rt6_qualify_for_ecmp() returns false if either of the conditions below
is true:

  1. f6i->fib6_flags has RTF_ADDRCONF
  2. f6i->nh is not NULL
  3. f6i->fib6_nh->fib_nh_gw_family is AF_UNSPEC

1 is unnecessary because rtm_to_fib6_config() never sets RTF_ADDRCONF
to cfg->fc_flags.

2. is equivalent with cfg->fc_nh_id.

3. can be replaced by checking RTF_GATEWAY in the base and each multipath
entry because AF_INET6 is set to f6i->fib6_nh->fib_nh_gw_family only when
cfg.fc_is_fdb is true or RTF_GATEWAY is set, but the former is always
false.

Let's perform the equivalent checks in rtm_to_fib6_multipath_config().

Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
 net/ipv6/route.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index baad02c099ff..b51793ee7a18 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -4996,6 +4996,7 @@ static int rtm_to_fib6_multipath_config(struct fib6_config *cfg,
 	}
 
 	do {
+		bool has_gateway = cfg->fc_flags & RTF_GATEWAY;
 		int attrlen = rtnh_attrlen(rtnh);
 
 		if (attrlen > 0) {
@@ -5009,9 +5010,17 @@ static int rtm_to_fib6_multipath_config(struct fib6_config *cfg,
 						       "Invalid IPv6 address in RTA_GATEWAY");
 					return -EINVAL;
 				}
+
+				has_gateway = true;
 			}
 		}
 
+		if (newroute && (cfg->fc_nh_id || !has_gateway)) {
+			NL_SET_ERR_MSG(extack,
+				       "Device only routes can not be added for IPv6 using the multipath API.");
+			return -EINVAL;
+		}
+
 		rtnh = rtnh_next(rtnh, &remaining);
 	} while (rtnh_ok(rtnh, remaining));
 
@@ -5353,13 +5362,6 @@ static int ip6_route_multipath_add(struct fib6_config *cfg,
 			rt = NULL;
 			goto cleanup;
 		}
-		if (!rt6_qualify_for_ecmp(rt)) {
-			err = -EINVAL;
-			NL_SET_ERR_MSG(extack,
-				       "Device only routes can not be added for IPv6 using the multipath API.");
-			fib6_info_release(rt);
-			goto cleanup;
-		}
 
 		rt->fib6_nh->fib_nh_weight = rtnh->rtnh_hops + 1;
 
-- 
2.48.1