[PATCH 3.2 21/27] ipv4: fix nexthop attlen check in fib_nh_match

[Ben Hutchings]

3.2.66-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Jiri Pirko <jiri@xxxxxxxxxxx>

commit f76936d07c4eeb36d8dbb64ebd30ab46ff85d9f7 upstream.

fib_nh_match does not match nexthops correctly. Example:

ip route add 172.16.10/24 nexthop via 192.168.122.12 dev eth0 \
                          nexthop via 192.168.122.13 dev eth0
ip route del 172.16.10/24 nexthop via 192.168.122.14 dev eth0 \
                          nexthop via 192.168.122.15 dev eth0

Del command is successful and route is removed. After this patch
applied, the route is correctly matched and result is:
RTNETLINK answers: No such process

Please consider this for stable trees as well.

Fixes: 4e902c57417c4 ("[IPv4]: FIB configuration using struct fib_config")
Signed-off-by: Jiri Pirko <jiri@xxxxxxxxxxx>
Acked-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/ipv4/fib_semantics.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -467,7 +467,7 @@ int fib_nh_match(struct fib_config *cfg,
 			return 1;
 
 		attrlen = rtnh_attrlen(rtnh);
-		if (attrlen < 0) {
+		if (attrlen > 0) {
 			struct nlattr *nla, *attrs = rtnh_attrs(rtnh);
 
 			nla = nla_find(attrs, attrlen, RTA_GATEWAY);

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