net/ipv6: Fix missing rcu dereferences on from

kbuild test robot reported 2 uses of rt->from not properly accessed
using rcu_dereference:
1. add rcu_dereference_protected to rt6_remove_exception_rt and make
   sure it is always called with rcu lock held.

2. change rt6_do_redirect to take a reference on 'from' when accessed
   the first time so it can be used the sceond time outside of the lock

Fixes: a68886a69180 ("net/ipv6: Make from in rt6_info rcu protected")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 354a5b8d016ffa37f7969aa13d6b3a02d3e31691..ac3e51631c659b5c5c8a93c17011cb7f3ad266e2 100644 (file)
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1541,11 +1541,13 @@ static struct rt6_info *rt6_find_cached_rt(struct fib6_info *rt,
 static int rt6_remove_exception_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;
        int err;
 
+       from = rcu_dereference_protected(rt->from,
+                                        lockdep_is_held(&rt6_exception_lock));
        if (!from ||
            !(rt->rt6i_flags & RTF_CACHE))
                return -EINVAL;
@@ -2223,6 +2225,7 @@ static void ip6_link_failure(struct sk_buff *skb)
 
        rt = (struct rt6_info *) skb_dst(skb);
        if (rt) {
+               rcu_read_lock();
                if (rt->rt6i_flags & RTF_CACHE) {
                        if (dst_hold_safe(&rt->dst))
                                rt6_remove_exception_rt(rt);
@@ -2230,15 +2233,14 @@ static void ip6_link_failure(struct sk_buff *skb)
                        struct fib6_info *from;
                        struct fib6_node *fn;
 
-                       rcu_read_lock();
                        from = rcu_dereference(rt->from);
                        if (from) {
                                fn = rcu_dereference(from->fib6_node);
                                if (fn && (rt->rt6i_flags & RTF_DEFAULT))
                                        fn->fn_sernum = -1;
                        }
-                       rcu_read_unlock();
                }
+               rcu_read_unlock();
        }
 }
 
@@ -3340,8 +3342,10 @@ static void rt6_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_bu
 
        rcu_read_lock();
        from = rcu_dereference(rt->from);
-       nrt = ip6_rt_cache_alloc(from, &msg->dest, NULL);
+       fib6_info_hold(from);
        rcu_read_unlock();
+
+       nrt = ip6_rt_cache_alloc(from, &msg->dest, NULL);
        if (!nrt)
                goto out;
 
@@ -3355,7 +3359,7 @@ static void rt6_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_bu
         * a cached route because rt6_insert_exception() will
         * takes care of it
         */
-       if (rt6_insert_exception(nrt, rt->from)) {
+       if (rt6_insert_exception(nrt, from)) {
                dst_release_immediate(&nrt->dst);
                goto out;
        }
@@ -3367,6 +3371,7 @@ static void rt6_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_bu
        call_netevent_notifiers(NETEVENT_REDIRECT, &netevent);
 
 out:
+       fib6_info_release(from);
        neigh_release(neigh);
 }