ipv6: check for ip6_null_entry in __ip6_del_rt_siblings()

Andrey reported a NULL pointer deref bug in ipv6_route_ioctl()
-> ip6_route_del() -> __ip6_del_rt_siblings() code path. This is
because ip6_null_entry is returned in this path since ip6_null_entry
is kinda default for a ipv6 route table root node. Quote from
David Ahern:

 ip6_null_entry is the root of all ipv6 fib tables making it integrated
 into the table ...

We should ignore any attempt of trying to delete it, like we do in
__ip6_del_rt() path and several others.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Fixes: 0ae8133586ad ("net: ipv6: Allow shorthand delete of all nexthops in multipath route")
Cc: David Ahern <dsa@cumulusnetworks.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 5 deletions

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index d94f1dfa54c8..43ca90d50ae9 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2169,10 +2169,13 @@ int ip6_del_rt(struct rt6_info *rt)
 static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
 {
         struct nl_info *info = &cfg->fc_nlinfo;
+        struct net *net = info->nl_net;
         struct sk_buff *skb = NULL;
         struct fib6_table *table;
-        int err;
+        int err = -ENOENT;
 
+        if (rt == net->ipv6.ip6_null_entry)
+                goto out_put;
         table = rt->rt6i_table;
         write_lock_bh(&table->tb6_lock);
 
@@ -2184,7 +2187,7 @@ static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
                 if (skb) {
                         u32 seq = info->nlh ? info->nlh->nlmsg_seq : 0;
 
-                        if (rt6_fill_node(info->nl_net, skb, rt,
+                        if (rt6_fill_node(net, skb, rt,
                                           NULL, NULL, 0, RTM_DELROUTE,
                                           info->portid, seq, 0) < 0) {
                                 kfree_skb(skb);
@@ -2198,17 +2201,18 @@ static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
                                          rt6i_siblings) {
                         err = fib6_del(sibling, info);
                         if (err)
-                                goto out;
+                                goto out_unlock;
                 }
         }
 
         err = fib6_del(rt, info);
-out:
+out_unlock:
         write_unlock_bh(&table->tb6_lock);
+out_put:
         ip6_rt_put(rt);
 
         if (skb) {
-                rtnl_notify(skb, info->nl_net, info->portid, RTNLGRP_IPV6_ROUTE,
+                rtnl_notify(skb, net, info->portid, RTNLGRP_IPV6_ROUTE,
                             info->nlh, gfp_any());
         }
         return err;