[PATCH 4.19 32/52] ipv6: route: enforce RCU protection in ip6_route_check_nh_onlink()

[Greg Kroah-Hartman]

4.19-stable review patch.  If anyone has any objections, please let me know.

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

From: Paolo Abeni <pab...@redhat.com>

[ 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 <pab...@redhat.com>
Reviewed-by: David Ahern <dsah...@gmail.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/ipv6/route.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2808,20 +2808,24 @@ static int ip6_route_check_nh_onlink(str
        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);
        }