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, 38 insertions, 70 deletions

diff --git a/net/batman-adv/multicast.c b/net/batman-adv/multicast.c
index 69244e4598f5..1dd70f048e7b 100644
--- a/net/batman-adv/multicast.c
+++ b/net/batman-adv/multicast.c
@@ -674,7 +674,7 @@ static void batadv_mcast_mla_update(struct work_struct *work)
  */
 static bool batadv_mcast_is_report_ipv4(struct sk_buff *skb)
 {
-	if (ip_mc_check_igmp(skb, NULL) < 0)
+	if (ip_mc_check_igmp(skb) < 0)
 		return false;
 
 	switch (igmp_hdr(skb)->type) {
@@ -741,7 +741,7 @@ static int batadv_mcast_forw_mode_check_ipv4(struct batadv_priv *bat_priv,
  */
 static bool batadv_mcast_is_report_ipv6(struct sk_buff *skb)
 {
-	if (ipv6_mc_check_mld(skb, NULL) < 0)
+	if (ipv6_mc_check_mld(skb) < 0)
 		return false;
 
 	switch (icmp6_hdr(skb)->icmp6_type) {
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 3aeff0895669..156c4905639e 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -938,7 +938,7 @@ static int br_ip4_multicast_igmp3_report(struct net_bridge *br,
 
 	for (i = 0; i < num; i++) {
 		len += sizeof(*grec);
-		if (!pskb_may_pull(skb, len))
+		if (!ip_mc_may_pull(skb, len))
 			return -EINVAL;
 
 		grec = (void *)(skb->data + len - sizeof(*grec));
@@ -946,7 +946,7 @@ static int br_ip4_multicast_igmp3_report(struct net_bridge *br,
 		type = grec->grec_type;
 
 		len += ntohs(grec->grec_nsrcs) * 4;
-		if (!pskb_may_pull(skb, len))
+		if (!ip_mc_may_pull(skb, len))
 			return -EINVAL;
 
 		/* We treat this as an IGMPv2 report for now. */
@@ -985,15 +985,17 @@ static int br_ip6_multicast_mld2_report(struct net_bridge *br,
 					struct sk_buff *skb,
 					u16 vid)
 {
+	unsigned int nsrcs_offset;
 	const unsigned char *src;
 	struct icmp6hdr *icmp6h;
 	struct mld2_grec *grec;
+	unsigned int grec_len;
 	int i;
 	int len;
 	int num;
 	int err = 0;
 
-	if (!pskb_may_pull(skb, sizeof(*icmp6h)))
+	if (!ipv6_mc_may_pull(skb, sizeof(*icmp6h)))
 		return -EINVAL;
 
 	icmp6h = icmp6_hdr(skb);
@@ -1003,21 +1005,25 @@ static int br_ip6_multicast_mld2_report(struct net_bridge *br,
 	for (i = 0; i < num; i++) {
 		__be16 *nsrcs, _nsrcs;
 
-		nsrcs = skb_header_pointer(skb,
-					   len + offsetof(struct mld2_grec,
-							  grec_nsrcs),
+		nsrcs_offset = len + offsetof(struct mld2_grec, grec_nsrcs);
+
+		if (skb_transport_offset(skb) + ipv6_transport_len(skb) <
+		    nsrcs_offset + sizeof(_nsrcs))
+			return -EINVAL;
+
+		nsrcs = skb_header_pointer(skb, nsrcs_offset,
 					   sizeof(_nsrcs), &_nsrcs);
 		if (!nsrcs)
 			return -EINVAL;
 
-		if (!pskb_may_pull(skb,
-				   len + sizeof(*grec) +
-				   sizeof(struct in6_addr) * ntohs(*nsrcs)))
+		grec_len = sizeof(*grec) +
+			   sizeof(struct in6_addr) * ntohs(*nsrcs);
+
+		if (!ipv6_mc_may_pull(skb, len + grec_len))
 			return -EINVAL;
 
 		grec = (struct mld2_grec *)(skb->data + len);
-		len += sizeof(*grec) +
-		       sizeof(struct in6_addr) * ntohs(*nsrcs);
+		len += grec_len;
 
 		/* We treat these as MLDv1 reports for now. */
 		switch (grec->grec_type) {
@@ -1219,6 +1225,7 @@ static void br_ip4_multicast_query(struct net_bridge *br,
 				   struct sk_buff *skb,
 				   u16 vid)
 {
+	unsigned int transport_len = ip_transport_len(skb);
 	const struct iphdr *iph = ip_hdr(skb);
 	struct igmphdr *ih = igmp_hdr(skb);
 	struct net_bridge_mdb_entry *mp;
@@ -1228,7 +1235,6 @@ static void br_ip4_multicast_query(struct net_bridge *br,
 	struct br_ip saddr;
 	unsigned long max_delay;
 	unsigned long now = jiffies;
-	unsigned int offset = skb_transport_offset(skb);
 	__be32 group;
 
 	spin_lock(&br->multicast_lock);
@@ -1238,14 +1244,14 @@ static void br_ip4_multicast_query(struct net_bridge *br,
 
 	group = ih->group;
 
-	if (skb->len == offset + sizeof(*ih)) {
+	if (transport_len == sizeof(*ih)) {
 		max_delay = ih->code * (HZ / IGMP_TIMER_SCALE);
 
 		if (!max_delay) {
 			max_delay = 10 * HZ;
 			group = 0;
 		}
-	} else if (skb->len >= offset + sizeof(*ih3)) {
+	} else if (transport_len >= sizeof(*ih3)) {
 		ih3 = igmpv3_query_hdr(skb);
 		if (ih3->nsrcs)
 			goto out;
@@ -1296,6 +1302,7 @@ static int br_ip6_multicast_query(struct net_bridge *br,
 				  struct sk_buff *skb,
 				  u16 vid)
 {
+	unsigned int transport_len = ipv6_transport_len(skb);
 	const struct ipv6hdr *ip6h = ipv6_hdr(skb);
 	struct mld_msg *mld;
 	struct net_bridge_mdb_entry *mp;
@@ -1315,7 +1322,7 @@ static int br_ip6_multicast_query(struct net_bridge *br,
 	    (port && port->state == BR_STATE_DISABLED))
 		goto out;
 
-	if (skb->len == offset + sizeof(*mld)) {
+	if (transport_len == sizeof(*mld)) {
 		if (!pskb_may_pull(skb, offset + sizeof(*mld))) {
 			err = -EINVAL;
 			goto out;
@@ -1581,12 +1588,11 @@ static int br_multicast_ipv4_rcv(struct net_bridge *br,
 				 struct sk_buff *skb,
 				 u16 vid)
 {
-	struct sk_buff *skb_trimmed = NULL;
 	const unsigned char *src;
 	struct igmphdr *ih;
 	int err;
 
-	err = ip_mc_check_igmp(skb, &skb_trimmed);
+	err = ip_mc_check_igmp(skb);
 
 	if (err == -ENOMSG) {
 		if (!ipv4_is_local_multicast(ip_hdr(skb)->daddr)) {
@@ -1612,19 +1618,16 @@ static int br_multicast_ipv4_rcv(struct net_bridge *br,
 		err = br_ip4_multicast_add_group(br, port, ih->group, vid, src);
 		break;
 	case IGMPV3_HOST_MEMBERSHIP_REPORT:
-		err = br_ip4_multicast_igmp3_report(br, port, skb_trimmed, vid);
+		err = br_ip4_multicast_igmp3_report(br, port, skb, vid);
 		break;
 	case IGMP_HOST_MEMBERSHIP_QUERY:
-		br_ip4_multicast_query(br, port, skb_trimmed, vid);
+		br_ip4_multicast_query(br, port, skb, vid);
 		break;
 	case IGMP_HOST_LEAVE_MESSAGE:
 		br_ip4_multicast_leave_group(br, port, ih->group, vid, src);
 		break;
 	}
 
-	if (skb_trimmed && skb_trimmed != skb)
-		kfree_skb(skb_trimmed);
-
 	br_multicast_count(br, port, skb, BR_INPUT_SKB_CB(skb)->igmp,
 			   BR_MCAST_DIR_RX);
 
@@ -1637,12 +1640,11 @@ static int br_multicast_ipv6_rcv(struct net_bridge *br,
 				 struct sk_buff *skb,
 				 u16 vid)
 {
-	struct sk_buff *skb_trimmed = NULL;
 	const unsigned char *src;
 	struct mld_msg *mld;
 	int err;
 
-	err = ipv6_mc_check_mld(skb, &skb_trimmed);
+	err = ipv6_mc_check_mld(skb);
 
 	if (err == -ENOMSG) {
 		if (!ipv6_addr_is_ll_all_nodes(&ipv6_hdr(skb)->daddr))
@@ -1664,10 +1666,10 @@ static int br_multicast_ipv6_rcv(struct net_bridge *br,
 						 src);
 		break;
 	case ICMPV6_MLD2_REPORT:
-		err = br_ip6_multicast_mld2_report(br, port, skb_trimmed, vid);
+		err = br_ip6_multicast_mld2_report(br, port, skb, vid);
 		break;
 	case ICMPV6_MGM_QUERY:
-		err = br_ip6_multicast_query(br, port, skb_trimmed, vid);
+		err = br_ip6_multicast_query(br, port, skb, vid);
 		break;
 	case ICMPV6_MGM_REDUCTION:
 		src = eth_hdr(skb)->h_source;
@@ -1675,9 +1677,6 @@ static int br_multicast_ipv6_rcv(struct net_bridge *br,
 		break;
 	}
 
-	if (skb_trimmed && skb_trimmed != skb)
-		kfree_skb(skb_trimmed);
-
 	br_multicast_count(br, port, skb, BR_INPUT_SKB_CB(skb)->igmp,
 			   BR_MCAST_DIR_RX);
 
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 765b2b32c4a4..b1f6d93282d7 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -1544,7 +1544,7 @@ static inline __sum16 ip_mc_validate_checksum(struct sk_buff *skb)
 	return skb_checksum_simple_validate(skb);
 }
 
-static int __ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed)
+static int __ip_mc_check_igmp(struct sk_buff *skb)
 
 {
 	struct sk_buff *skb_chk;
@@ -1566,16 +1566,10 @@ static int __ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed)
 	if (ret)
 		goto err;
 
-	if (skb_trimmed)
-		*skb_trimmed = skb_chk;
-	/* free now unneeded clone */
-	else if (skb_chk != skb)
-		kfree_skb(skb_chk);
-
 	ret = 0;
 
 err:
-	if (ret && skb_chk && skb_chk != skb)
+	if (skb_chk && skb_chk != skb)
 		kfree_skb(skb_chk);
 
 	return ret;
@@ -1584,7 +1578,6 @@ err:
 /**
  * ip_mc_check_igmp - checks whether this is a sane IGMP packet
  * @skb: the skb to validate
- * @skb_trimmed: to store an skb pointer trimmed to IPv4 packet tail (optional)
  *
  * Checks whether an IPv4 packet is a valid IGMP packet. If so sets
  * skb transport header accordingly and returns zero.
@@ -1594,18 +1587,10 @@ err:
  * -ENOMSG: IP header validation succeeded but it is not an IGMP packet.
  * -ENOMEM: A memory allocation failure happened.
  *
- * Optionally, an skb pointer might be provided via skb_trimmed (or set it
- * to NULL): After parsing an IGMP packet successfully it will point to
- * an skb which has its tail aligned to the IP packet end. This might
- * either be the originally provided skb or a trimmed, cloned version if
- * the skb frame had data beyond the IP packet. A cloned skb allows us
- * to leave the original skb and its full frame unchanged (which might be
- * desirable for layer 2 frame jugglers).
- *
  * Caller needs to set the skb network header and free any returned skb if it
  * differs from the provided skb.
  */
-int ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed)
+int ip_mc_check_igmp(struct sk_buff *skb)
 {
 	int ret = ip_mc_check_iphdr(skb);
 
@@ -1615,7 +1600,7 @@ int ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed)
 	if (ip_hdr(skb)->protocol != IPPROTO_IGMP)
 		return -ENOMSG;
 
-	return __ip_mc_check_igmp(skb, skb_trimmed);
+	return __ip_mc_check_igmp(skb);
 }
 EXPORT_SYMBOL(ip_mc_check_igmp);
 
diff --git a/net/ipv6/mcast_snoop.c b/net/ipv6/mcast_snoop.c
index 9405b04eecc6..1a917dc80d5e 100644
--- a/net/ipv6/mcast_snoop.c
+++ b/net/ipv6/mcast_snoop.c
@@ -136,8 +136,7 @@ static inline __sum16 ipv6_mc_validate_checksum(struct sk_buff *skb)
 	return skb_checksum_validate(skb, IPPROTO_ICMPV6, ip6_compute_pseudo);
 }
 
-static int __ipv6_mc_check_mld(struct sk_buff *skb,
-			       struct sk_buff **skb_trimmed)
+static int __ipv6_mc_check_mld(struct sk_buff *skb)
 
 {
 	struct sk_buff *skb_chk = NULL;
@@ -160,16 +159,10 @@ static int __ipv6_mc_check_mld(struct sk_buff *skb,
 	if (ret)
 		goto err;
 
-	if (skb_trimmed)
-		*skb_trimmed = skb_chk;
-	/* free now unneeded clone */
-	else if (skb_chk != skb)
-		kfree_skb(skb_chk);
-
 	ret = 0;
 
 err:
-	if (ret && skb_chk && skb_chk != skb)
+	if (skb_chk && skb_chk != skb)
 		kfree_skb(skb_chk);
 
 	return ret;
@@ -178,7 +171,6 @@ err:
 /**
  * ipv6_mc_check_mld - checks whether this is a sane MLD packet
  * @skb: the skb to validate
- * @skb_trimmed: to store an skb pointer trimmed to IPv6 packet tail (optional)
  *
  * Checks whether an IPv6 packet is a valid MLD packet. If so sets
  * skb transport header accordingly and returns zero.
@@ -188,18 +180,10 @@ err:
  * -ENOMSG: IP header validation succeeded but it is not an MLD packet.
  * -ENOMEM: A memory allocation failure happened.
  *
- * Optionally, an skb pointer might be provided via skb_trimmed (or set it
- * to NULL): After parsing an MLD packet successfully it will point to
- * an skb which has its tail aligned to the IP packet end. This might
- * either be the originally provided skb or a trimmed, cloned version if
- * the skb frame had data beyond the IP packet. A cloned skb allows us
- * to leave the original skb and its full frame unchanged (which might be
- * desirable for layer 2 frame jugglers).
- *
  * Caller needs to set the skb network header and free any returned skb if it
  * differs from the provided skb.
  */
-int ipv6_mc_check_mld(struct sk_buff *skb, struct sk_buff **skb_trimmed)
+int ipv6_mc_check_mld(struct sk_buff *skb)
 {
 	int ret;
 
@@ -211,6 +195,6 @@ int ipv6_mc_check_mld(struct sk_buff *skb, struct sk_buff **skb_trimmed)
 	if (ret < 0)
 		return ret;
 
-	return __ipv6_mc_check_mld(skb, skb_trimmed);
+	return __ipv6_mc_check_mld(skb);
 }
 EXPORT_SYMBOL(ipv6_mc_check_mld);