netdev - [PATCH net 1/2] ipv6: route: enforce RCU protection in rt6_update_exception_stamp

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Message-Id: <1ac484e7626a5d5e7c22de13485575de30ad7fe0.1550682516.git.pabeni@redhat.com>
Date:   Wed, 20 Feb 2019 18:10:26 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     David Ahern <dsahern@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH net 1/2] ipv6: route: enforce RCU protection in rt6_update_exception_stamp_rt()

We must access rt6_info->from under RCU read lock: move the
dereference under such lock, with proper annotation, and use
rcu_access_pointer() to check for null value outside the lock.

Fixes: a68886a69180 ("net/ipv6: Make from in rt6_info rcu protected")
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
 net/ipv6/route.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index bd09abd1fb22..cbaa8745d9ff 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;
+	struct fib6_info *from;
 
-	if (!from ||
-	    !(rt->rt6i_flags & RTF_CACHE))
+	if (!rcu_access_pointer(rt->from) || !(rt->rt6i_flags & RTF_CACHE))
 		return;
 
 	rcu_read_lock();
+	from = rcu_dereference(rt->from);
 	bucket = rcu_dereference(from->rt6i_exception_bucket);
 
 #ifdef CONFIG_IPV6_SUBTREES
-- 
2.20.1