[PATCH] ipmr: validate IPv4 header length in reg_vif_xmit() and zero iphdr in ipmr_get_route()

[Hui Peng <benquike@gmail.com>]

Fix two bugs in IPv4 multicast routing:

1. In reg_vif_xmit() (net/ipv4/ipmr.c), verify that the skb contains a
   full IPv4 header with ihl >= 5 before reading ip_hdr(skb) and passing
   the encapsulated PIM register packet to ipmr_cache_report().
2. In ipmr_get_route() and inet_rtm_getroute() (net/ipv4/route.c), zero-
   initialize the synthetic IPv4 header pushed onto the RTM_GETROUTE
   probe skb so uninitialized slab bytes in iph->ihl / iph->tos /
   iph->frag_off do not corrupt fib_multipath_hash() or
   ipmr_cache_alloc().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>
---
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index b9c544d48c45..8242ab62d1b3 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -545,6 +545,13 @@ static netdev_tx_t reg_vif_xmit(struct sk_buff *skb, struct net_device *dev)
 		return err;
 	}
 
+	if (!pskb_may_pull(skb, sizeof(struct iphdr))) {
+		DEV_STATS_INC(dev, tx_dropped);
+		rcu_read_unlock();
+		kfree_skb(skb);
+		return NETDEV_TX_OK;
+	}
+
 	DEV_STATS_ADD(dev, tx_bytes, skb->len);
 	DEV_STATS_INC(dev, tx_packets);
 
@@ -2492,6 +2499,7 @@ int ipmr_get_route(struct net *net, struct sk_buff *skb,
 		skb_push(skb2, sizeof(struct iphdr));
 		skb_reset_network_header(skb2);
 		iph = ip_hdr(skb2);
+		memset(iph, 0, sizeof(*iph));
 		iph->ihl = sizeof(struct iphdr) >> 2;
 		iph->saddr = saddr;
 		iph->daddr = daddr;
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 37674d76f90f..1cba70e38507 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -3087,8 +3087,10 @@ static int rt_fill_info(struct net *net, __be32 dst, __be32 src,
 							 r, portid);
 
 				if (err <= 0) {
-					if (err == 0)
+					if (err == 0) {
+						nlmsg_end(skb, nlh);
 						return 0;
+					}
 					goto nla_put_failure;
 				}
 			} else