[IPV4] ipmr: ip multicast route bug fix.

IP multicast route code was reusing an skb which causes use after free
and double free.

From: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>

Note, it is real skb_clone(), not alloc_skb(). Equeued skb contains
the whole half-prepared netlink message plus room for the rest.
It could be also skb_copy(), if we want to be puristic about mangling
cloned data, but original copy is really not going to be used.  

Acked-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 6 deletions

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 9ccacf57f08b..85893eef6b16 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1578,6 +1578,7 @@ int ipmr_get_route(struct sk_buff *skb, struct rtmsg *rtm, int nowait)
         cache = ipmr_cache_find(rt->rt_src, rt->rt_dst);
 
         if (cache==NULL) {
+                struct sk_buff *skb2;
                 struct net_device *dev;
                 int vif;
 
@@ -1591,12 +1592,18 @@ int ipmr_get_route(struct sk_buff *skb, struct rtmsg *rtm, int nowait)
                         read_unlock(&mrt_lock);
                         return -ENODEV;
                 }
-                skb->nh.raw = skb_push(skb, sizeof(struct iphdr));
-                skb->nh.iph->ihl = sizeof(struct iphdr)>>2;
-                skb->nh.iph->saddr = rt->rt_src;
-                skb->nh.iph->daddr = rt->rt_dst;
-                skb->nh.iph->version = 0;
-                err = ipmr_cache_unresolved(vif, skb);
+                skb2 = skb_clone(skb, GFP_ATOMIC);
+                if (!skb2) {
+                        read_unlock(&mrt_lock);
+                        return -ENOMEM;
+                }
+
+                skb2->nh.raw = skb_push(skb2, sizeof(struct iphdr));
+                skb2->nh.iph->ihl = sizeof(struct iphdr)>>2;
+                skb2->nh.iph->saddr = rt->rt_src;
+                skb2->nh.iph->daddr = rt->rt_dst;
+                skb2->nh.iph->version = 0;
+                err = ipmr_cache_unresolved(vif, skb2);
                 read_unlock(&mrt_lock);
                 return err;
         }