netfilter: Fix potential use after free in ip6_route_me_harder()

Dst is released one line before we access it again with dst->error.

Fixes: 58e35d147128 netfilter: ipv6: propagate routing errors from
ip6_route_me_harder()

Signed-off-by: Sergey Popovich <popovich_sergei@mail.ru>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/ipv6/netfilter.c b/net/ipv6/netfilter.c
index 95f3f1da0d7f..d38e6a8d8b9f 100644
--- a/net/ipv6/netfilter.c
+++ b/net/ipv6/netfilter.c
@@ -30,13 +30,15 @@ int ip6_route_me_harder(struct sk_buff *skb)
                 .daddr = iph->daddr,
                 .saddr = iph->saddr,
         };
+        int err;
 
         dst = ip6_route_output(net, skb->sk, &fl6);
-        if (dst->error) {
+        err = dst->error;
+        if (err) {
                 IP6_INC_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTNOROUTES);
                 LIMIT_NETDEBUG(KERN_DEBUG "ip6_route_me_harder: No more route.\n");
                 dst_release(dst);
-                return dst->error;
+                return err;
         }
 
         /* Drop old route. */