bridge: simplify ip_mc_check_igmp() and ipv6_mc_check_mld() calls

This patch refactors ip_mc_check_igmp(), ipv6_mc_check_mld() and
their callers (more precisely, the Linux bridge) to not rely on
the skb_trimmed parameter anymore.

An skb with its tail trimmed to the IP packet length was initially
introduced for the following three reasons:

1) To be able to verify the ICMPv6 checksum.
2) To be able to distinguish the version of an IGMP or MLD query.
   They are distinguishable only by their size.
3) To avoid parsing data for an IGMPv3 or MLDv2 report that is
   beyond the IP packet but still within the skb.

The first case still uses a cloned and potentially trimmed skb to
verfiy. However, there is no need to propagate it to the caller.
For the second and third case explicit IP packet length checks were
added.

This hopefully makes ip_mc_check_igmp() and ipv6_mc_check_mld() easier
to read and verfiy, as well as easier to use.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 32 insertions, 2 deletions

diff --git a/include/linux/igmp.h b/include/linux/igmp.h
index 119f53941c12..8b4348f69bc5 100644
--- a/include/linux/igmp.h
+++ b/include/linux/igmp.h
@@ -18,6 +18,7 @@
 #include <linux/skbuff.h>
 #include <linux/timer.h>
 #include <linux/in.h>
+#include <linux/ip.h>
 #include <linux/refcount.h>
 #include <uapi/linux/igmp.h>
 
@@ -106,6 +107,14 @@ struct ip_mc_list {
 #define IGMPV3_QQIC(value) IGMPV3_EXP(0x80, 4, 3, value)
 #define IGMPV3_MRC(value) IGMPV3_EXP(0x80, 4, 3, value)
 
+static inline int ip_mc_may_pull(struct sk_buff *skb, unsigned int len)
+{
+	if (skb_transport_offset(skb) + ip_transport_len(skb) < len)
+		return -EINVAL;
+
+	return pskb_may_pull(skb, len);
+}
+
 extern int ip_check_mc_rcu(struct in_device *dev, __be32 mc_addr, __be32 src_addr, u8 proto);
 extern int igmp_rcv(struct sk_buff *);
 extern int ip_mc_join_group(struct sock *sk, struct ip_mreqn *imr);
@@ -130,6 +139,6 @@ extern void ip_mc_unmap(struct in_device *);
 extern void ip_mc_remap(struct in_device *);
 extern void ip_mc_dec_group(struct in_device *in_dev, __be32 addr);
 extern void ip_mc_inc_group(struct in_device *in_dev, __be32 addr);
-int ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed);
+int ip_mc_check_igmp(struct sk_buff *skb);
 
 #endif
diff --git a/include/linux/ip.h b/include/linux/ip.h
index 492bc6513533..482b7b7c9f30 100644
--- a/include/linux/ip.h
+++ b/include/linux/ip.h
@@ -34,4 +34,9 @@ static inline struct iphdr *ipip_hdr(const struct sk_buff *skb)
 {
 	return (struct iphdr *)skb_transport_header(skb);
 }
+
+static inline unsigned int ip_transport_len(const struct sk_buff *skb)
+{
+	return ntohs(ip_hdr(skb)->tot_len) - skb_network_header_len(skb);
+}
 #endif	/* _LINUX_IP_H */
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 495e834c1367..6d45ce784bea 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -104,6 +104,12 @@ static inline struct ipv6hdr *ipipv6_hdr(const struct sk_buff *skb)
 	return (struct ipv6hdr *)skb_transport_header(skb);
 }
 
+static inline unsigned int ipv6_transport_len(const struct sk_buff *skb)
+{
+	return ntohs(ipv6_hdr(skb)->payload_len) + sizeof(struct ipv6hdr) -
+	       skb_network_header_len(skb);
+}
+
 /* 
    This structure contains results of exthdrs parsing
    as offsets from skb->nh.
diff --git a/include/net/addrconf.h b/include/net/addrconf.h
index 1656c5978498..daf11dcb0f70 100644
--- a/include/net/addrconf.h
+++ b/include/net/addrconf.h
@@ -49,6 +49,7 @@ struct prefix_info {
 	struct in6_addr		prefix;
 };
 
+#include <linux/ipv6.h>
 #include <linux/netdevice.h>
 #include <net/if_inet6.h>
 #include <net/ipv6.h>
@@ -201,6 +202,15 @@ u32 ipv6_addr_label(struct net *net, const struct in6_addr *addr,
 /*
  *	multicast prototypes (mcast.c)
  */
+static inline int ipv6_mc_may_pull(struct sk_buff *skb,
+				   unsigned int len)
+{
+	if (skb_transport_offset(skb) + ipv6_transport_len(skb) < len)
+		return -EINVAL;
+
+	return pskb_may_pull(skb, len);
+}
+
 int ipv6_sock_mc_join(struct sock *sk, int ifindex,
 		      const struct in6_addr *addr);
 int ipv6_sock_mc_drop(struct sock *sk, int ifindex,
@@ -219,7 +229,7 @@ void ipv6_mc_unmap(struct inet6_dev *idev);
 void ipv6_mc_remap(struct inet6_dev *idev);
 void ipv6_mc_init_dev(struct inet6_dev *idev);
 void ipv6_mc_destroy_dev(struct inet6_dev *idev);
-int ipv6_mc_check_mld(struct sk_buff *skb, struct sk_buff **skb_trimmed);
+int ipv6_mc_check_mld(struct sk_buff *skb);
 void addrconf_dad_failure(struct sk_buff *skb, struct inet6_ifaddr *ifp);
 
 bool ipv6_chk_mcast_addr(struct net_device *dev, const struct in6_addr *group,