ipv6: fix null pointer dereference in __ip6addrlbl_add

Commit b67bfe0d42cac56c512dd5da4b1b347a23f4b70a ("hlist: drop
the node parameter from iterators") changed the behavior of
hlist_for_each_entry_safe to leave the p argument NULL.

Fix this up by tracking the last argument.

Reported-by: Michele Baldessari <michele@acksyn.org>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Tested-by: Michele Baldessari <michele@acksyn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 23 insertions, 25 deletions

diff --git a/net/ipv6/addrlabel.c b/net/ipv6/addrlabel.c
index f083a583a05c..b30ad3741b46 100644
--- a/net/ipv6/addrlabel.c
+++ b/net/ipv6/addrlabel.c
@@ -251,38 +251,36 @@ static struct ip6addrlbl_entry *ip6addrlbl_alloc(struct net *net,
 /* add a label */
 static int __ip6addrlbl_add(struct ip6addrlbl_entry *newp, int replace)
 {
+        struct hlist_node *n;
+        struct ip6addrlbl_entry *last = NULL, *p = NULL;
         int ret = 0;
 
-        ADDRLABEL(KERN_DEBUG "%s(newp=%p, replace=%d)\n",
-                        __func__,
-                        newp, replace);
+        ADDRLABEL(KERN_DEBUG "%s(newp=%p, replace=%d)\n", __func__, newp,
+                  replace);
 
-        if (hlist_empty(&ip6addrlbl_table.head)) {
-                hlist_add_head_rcu(&newp->list, &ip6addrlbl_table.head);
-        } else {
-                struct hlist_node *n;
-                struct ip6addrlbl_entry *p = NULL;
-                hlist_for_each_entry_safe(p, n,
-                                          &ip6addrlbl_table.head, list) {
-                        if (p->prefixlen == newp->prefixlen &&
-                            net_eq(ip6addrlbl_net(p), ip6addrlbl_net(newp)) &&
-                            p->ifindex == newp->ifindex &&
-                            ipv6_addr_equal(&p->prefix, &newp->prefix)) {
-                                if (!replace) {
-                                        ret = -EEXIST;
-                                        goto out;
-                                }
-                                hlist_replace_rcu(&p->list, &newp->list);
-                                ip6addrlbl_put(p);
-                                goto out;
-                        } else if ((p->prefixlen == newp->prefixlen && !p->ifindex) ||
-                                   (p->prefixlen < newp->prefixlen)) {
-                                hlist_add_before_rcu(&newp->list, &p->list);
+        hlist_for_each_entry_safe(p, n, &ip6addrlbl_table.head, list) {
+                if (p->prefixlen == newp->prefixlen &&
+                    net_eq(ip6addrlbl_net(p), ip6addrlbl_net(newp)) &&
+                    p->ifindex == newp->ifindex &&
+                    ipv6_addr_equal(&p->prefix, &newp->prefix)) {
+                        if (!replace) {
+                                ret = -EEXIST;
                                 goto out;
                         }
+                        hlist_replace_rcu(&p->list, &newp->list);
+                        ip6addrlbl_put(p);
+                        goto out;
+                } else if ((p->prefixlen == newp->prefixlen && !p->ifindex) ||
+                           (p->prefixlen < newp->prefixlen)) {
+                        hlist_add_before_rcu(&newp->list, &p->list);
+                        goto out;
                 }
-                hlist_add_after_rcu(&p->list, &newp->list);
+                last = p;
         }
+        if (last)
+                hlist_add_after_rcu(&last->list, &newp->list);
+        else
+                hlist_add_head_rcu(&newp->list, &ip6addrlbl_table.head);
 out:
         if (!ret)
                 ip6addrlbl_table.seq++;