Subject: [PATCH 35/38] ipv6: route: enforce RCU protection in ip6_route_check_nh_onlink()

From: Paolo Abeni <[email-masked]>
Date: Thu, 21 Feb 2019 11:19:42 +0100

[ Upstream commit bf1dc8bad1d42287164d216d8efb51c5cd381b18 ]

We need a RCU critical section around rt6_info->from deference, and
proper annotation.

Fixes: 4ed591c8ab44 ("net/ipv6: Allow onlink routes to have a device mismatch if it is the default route")
Signed-off-by: Paolo Abeni <[email-masked]>
Reviewed-by: David Ahern <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/ipv6/route.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 7e21797d7ae8..603488cf132d 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2752,20 +2752,24 @@ static int ip6_route_check_nh_onlink(struct net *net,
 	u32 tbid = l3mdev_fib_table(dev) ? : RT_TABLE_MAIN;
 	const struct in6_addr *gw_addr = &cfg->fc_gateway;
 	u32 flags = RTF_LOCAL | RTF_ANYCAST | RTF_REJECT;
+	struct fib6_info *from;
 	struct rt6_info *grt;
 	int err;
 
 	err = 0;
 	grt = ip6_nh_lookup_table(net, cfg, gw_addr, tbid, 0);
 	if (grt) {
+		rcu_read_lock();
+		from = rcu_dereference(grt->from);
 		if (!grt->dst.error &&
 		    /* ignore match if it is the default route */
-		    grt->from && !ipv6_addr_any(&grt->from->fib6_dst.addr) &&
+		    from && !ipv6_addr_any(&from->fib6_dst.addr) &&
 		    (grt->rt6i_flags & flags || dev != grt->dst.dev)) {
 			NL_SET_ERR_MSG(extack,
 				       "Nexthop has invalid gateway or device mismatch");
 			err = -EINVAL;
 		}
+		rcu_read_unlock();
 
 		ip6_rt_put(grt);
 	}
-- 
2.20.1