ipv6: make ip6_create_rt_rcu return ip6_null_entry instead of NULL

Jianlin reported a crash:

  [  381.484332] BUG: unable to handle kernel NULL pointer dereference at 0000000000000068
  [  381.619802] RIP: 0010:fib6_rule_lookup+0xa3/0x160
  [  382.009615] Call Trace:
  [  382.020762]  <IRQ>
  [  382.030174]  ip6_route_redirect.isra.52+0xc9/0xf0
  [  382.050984]  ip6_redirect+0xb6/0xf0
  [  382.066731]  icmpv6_notify+0xca/0x190
  [  382.083185]  ndisc_redirect_rcv+0x10f/0x160
  [  382.102569]  ndisc_rcv+0xfb/0x100
  [  382.117725]  icmpv6_rcv+0x3f2/0x520
  [  382.133637]  ip6_input_finish+0xbf/0x460
  [  382.151634]  ip6_input+0x3b/0xb0
  [  382.166097]  ipv6_rcv+0x378/0x4e0

It was caused by the lookup function __ip6_route_redirect() returns NULL in
fib6_rule_lookup() when ip6_create_rt_rcu() returns NULL.

So we fix it by simply making ip6_create_rt_rcu() return ip6_null_entry
instead of NULL.

v1->v2:
  - move down 'fallback:' to make it more readable.

Fixes: e873e4b9cc7e ("ipv6: use fib6_info_hold_safe() when necessary")
Reported-by: Jianlin Shi <jishi@redhat.com>
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Acked-by: Wei Wang <weiwan@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 4ef4bbdb49d4b203974bf95de47534921baed3f6..0302e0eb07af1d270a615bcadfcb9bc08ca61d6c 100644 (file)
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1040,14 +1040,20 @@ static struct rt6_info *ip6_create_rt_rcu(struct fib6_info *rt)
        struct rt6_info *nrt;
 
        if (!fib6_info_hold_safe(rt))
-               return NULL;
+               goto fallback;
 
        nrt = ip6_dst_alloc(dev_net(dev), dev, flags);
-       if (nrt)
-               ip6_rt_copy_init(nrt, rt);
-       else
+       if (!nrt) {
                fib6_info_release(rt);
+               goto fallback;
+       }
 
+       ip6_rt_copy_init(nrt, rt);
+       return nrt;
+
+fallback:
+       nrt = dev_net(dev)->ipv6.ip6_null_entry;
+       dst_hold(&nrt->dst);
        return nrt;
 }
 
@@ -1096,10 +1102,6 @@ restart:
                dst_hold(&rt->dst);
        } else {
                rt = ip6_create_rt_rcu(f6i);
-               if (!rt) {
-                       rt = net->ipv6.ip6_null_entry;
-                       dst_hold(&rt->dst);
-               }
        }
 
        rcu_read_unlock();