[IPV4]: OOPS with NETLINK_FIB_LOOKUP netlink socket

[ Regression added by changeset:
	cd40b7d3983c708aabe3d3008ec64ffce56d33b0
	[NET]: make netlink user -> kernel interface synchronious
  -DaveM ]

nl_fib_input re-reuses incoming skb to send the reply. This means that this
packet will be freed twice, namely in:
- netlink_unicast_kernel
- on receive path
Use clone to send as a cure, the caller is responsible for kfree_skb on error.

Thanks to Alexey Dobryan, who originally found the problem.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 3 deletions

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 732d8f088b13..97abf934d185 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -804,10 +804,13 @@ static void nl_fib_input(struct sk_buff *skb)
 
         nlh = nlmsg_hdr(skb);
         if (skb->len < NLMSG_SPACE(0) || skb->len < nlh->nlmsg_len ||
-            nlh->nlmsg_len < NLMSG_LENGTH(sizeof(*frn))) {
-                kfree_skb(skb);
+            nlh->nlmsg_len < NLMSG_LENGTH(sizeof(*frn)))
                 return;
-        }
+
+        skb = skb_clone(skb, GFP_KERNEL);
+        if (skb == NULL)
+                return;
+        nlh = nlmsg_hdr(skb);
 
         frn = (struct fib_result_nl *) NLMSG_DATA(nlh);
         tb = fib_get_table(frn->tb_id_in);