[PATCH net v2 1/2] ipv6: route: enforce RCU protection in rt6_update_exception_stamp_rt()

[Paolo Abeni]

We must access rt6_info->from under RCU read lock: move the
dereference under such lock, with proper annotation.

v1 -> v2:
 - avoid using multiple, racy, fetch operations for rt->from

Fixes: a68886a69180 ("net/ipv6: Make from in rt6_info rcu protected")
Signed-off-by: Paolo Abeni <pab...@redhat.com>
---
 net/ipv6/route.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index bd09abd1fb22..1597a3746b40 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1610,15 +1610,15 @@ static int rt6_remove_exception_rt(struct rt6_info *rt)
 static void rt6_update_exception_stamp_rt(struct rt6_info *rt)
 {
        struct rt6_exception_bucket *bucket;
-       struct fib6_info *from = rt->from;
        struct in6_addr *src_key = NULL;
        struct rt6_exception *rt6_ex;
-
-       if (!from ||
-           !(rt->rt6i_flags & RTF_CACHE))
-               return;
+       struct fib6_info *from;
 
        rcu_read_lock();
+       from = rcu_dereference(rt->from);
+       if (!from || !(rt->rt6i_flags & RTF_CACHE))
+               goto unlock;
+
        bucket = rcu_dereference(from->rt6i_exception_bucket);
 
 #ifdef CONFIG_IPV6_SUBTREES
@@ -1637,6 +1637,7 @@ static void rt6_update_exception_stamp_rt(struct rt6_info 
*rt)
        if (rt6_ex)
                rt6_ex->stamp = jiffies;
 
+unlock:
        rcu_read_unlock();
 }
 
-- 
2.20.1