Linux Ethernet Bridging - May 2015 - [Bridge] [PATCHv3 net-next 1/2] bridge: multicast: call skb_checksum_{simple_, }validate

The multicast optimizations in batman-adv are yet only usable and
enabled in non-bridged scenarios. To be able to support bridged setups
batman-adv needs to be able to detect IGMP/MLD queriers and reports on
mesh nodes without bridges, too. See the following link for details:

http://www.open-mesh.org/projects/batman-adv/wiki/Multicast-optimizations-listener-reports

To avoid duplicate code between the bridge and batman-adv, the IGMP/MLD
message validation code is moved from the bridge to the IPv4/IPv6 stack.

On the way, some refactoring to increase readability and to iron out
some subtle differences between the IGMP and MLD parsing code is done.

Cheers, Linus


Changelog v3:
* changed interface / restructuring of skb_checksum_trimmed()
* kernel doc for skb_checksum_trimmed()/skb_checksum_maybe_trim()
* fixed a memory leak in the cloned skb case in skb_checksum_trimmed()
* fixed transport_len calculation in __ipv6_mc_check_mld(),
  make it relative to the skb transport header offset
  (= exclude the hop-by-hop option size in transport_len)

Changelog v2:
* Updated copyright for mcast_snoop.c

Let's use these new, neat helpers.

Signed-off-by: Linus L?ssing <linus.luessing at c0d3.blue>
---
 net/bridge/br_multicast.c |   28 ++++------------------------
 1 file changed, 4 insertions(+), 24 deletions(-)

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 4b6722f..b52f4cb 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1610,16 +1610,8 @@ static int br_multicast_ipv4_rcv(struct net_bridge *br,
 	if (!pskb_may_pull(skb2, sizeof(*ih)))
 		goto out;
 
-	switch (skb2->ip_summed) {
-	case CHECKSUM_COMPLETE:
-		if (!csum_fold(skb2->csum))
-			break;
-		/* fall through */
-	case CHECKSUM_NONE:
-		skb2->csum = 0;
-		if (skb_checksum_complete(skb2))
-			goto out;
-	}
+	if (skb_checksum_simple_validate(skb2))
+		goto out;
 
 	err = 0;
 
@@ -1737,20 +1729,8 @@ static int br_multicast_ipv6_rcv(struct net_bridge *br,
 
 	ip6h = ipv6_hdr(skb2);
 
-	switch (skb2->ip_summed) {
-	case CHECKSUM_COMPLETE:
-		if (!csum_ipv6_magic(&ip6h->saddr, &ip6h->daddr, skb2->len,
-					IPPROTO_ICMPV6, skb2->csum))
-			break;
-		/*FALLTHROUGH*/
-	case CHECKSUM_NONE:
-		skb2->csum = ~csum_unfold(csum_ipv6_magic(&ip6h->saddr,
-							&ip6h->daddr,
-							skb2->len,
-							IPPROTO_ICMPV6, 0));
-		if (__skb_checksum_complete(skb2))
-			goto out;
-	}
+	if (skb_checksum_validate(skb2, IPPROTO_ICMPV6, ip6_compute_pseudo))
+		goto out;
 
 	err = 0;
 
-- 
1.7.10.4

With this patch, the IGMP and MLD message validation functions are moved
from the bridge code to IPv4/IPv6 multicast files. Some small
refactoring was done to enhance readibility and to iron out some
differences in behaviour between the IGMP and MLD parsing code (e.g. the
skb-cloning of MLD messages is now only done if necessary, just like the
IGMP part always did).

Finally, these IGMP and MLD message validation functions are exported so
that not only the bridge can use it but batman-adv later, too.

Signed-off-by: Linus L?ssing <linus.luessing at c0d3.blue>
---
 include/linux/igmp.h      |    1 +
 include/linux/skbuff.h    |    3 +
 include/net/addrconf.h    |    1 +
 net/bridge/br_multicast.c |  218 +++++++--------------------------------------
 net/core/skbuff.c         |   87 ++++++++++++++++++
 net/ipv4/igmp.c           |  162 +++++++++++++++++++++++++++++++++
 net/ipv6/Makefile         |    1 +
 net/ipv6/mcast_snoop.c    |  213 +++++++++++++++++++++++++++++++++++++++++++
 8 files changed, 498 insertions(+), 188 deletions(-)
 create mode 100644 net/ipv6/mcast_snoop.c

diff --git a/include/linux/igmp.h b/include/linux/igmp.h
index 2c677af..193ad48 100644
--- a/include/linux/igmp.h
+++ b/include/linux/igmp.h
@@ -130,5 +130,6 @@ 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);
 
 #endif
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 66e374d..cd34010 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3417,6 +3417,9 @@ static inline void skb_checksum_none_assert(const struct
sk_buff *skb)
 bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off);
 
 int skb_checksum_setup(struct sk_buff *skb, bool recalculate);
+struct sk_buff *skb_checksum_trimmed(struct sk_buff *skb,
+				     unsigned int transport_len,
+				     __sum16(*skb_chkf)(struct sk_buff *skb));
 
 u32 skb_get_poff(const struct sk_buff *skb);
 u32 __skb_get_poff(const struct sk_buff *skb, void *data,
diff --git a/include/net/addrconf.h b/include/net/addrconf.h
index 80456f7..def59d3 100644
--- a/include/net/addrconf.h
+++ b/include/net/addrconf.h
@@ -142,6 +142,7 @@ 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);
 void addrconf_dad_failure(struct inet6_ifaddr *ifp);
 
 bool ipv6_chk_mcast_addr(struct net_device *dev, const struct in6_addr *group,
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index b52f4cb..2d69d5c 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -975,9 +975,6 @@ static int br_ip4_multicast_igmp3_report(struct net_bridge
*br,
 	int err = 0;
 	__be32 group;
 
-	if (!pskb_may_pull(skb, sizeof(*ih)))
-		return -EINVAL;
-
 	ih = igmpv3_report_hdr(skb);
 	num = ntohs(ih->ngrec);
 	len = sizeof(*ih);
@@ -1248,25 +1245,14 @@ static int br_ip4_multicast_query(struct net_bridge *br,
 			max_delay = 10 * HZ;
 			group = 0;
 		}
-	} else {
-		if (!pskb_may_pull(skb, sizeof(struct igmpv3_query))) {
-			err = -EINVAL;
-			goto out;
-		}
-
+	} else if (skb->len >= sizeof(*ih3)) {
 		ih3 = igmpv3_query_hdr(skb);
 		if (ih3->nsrcs)
 			goto out;
 
 		max_delay = ih3->code ?
 			    IGMPV3_MRC(ih3->code) * (HZ / IGMP_TIMER_SCALE) : 1;
-	}
-
-	/* RFC2236+RFC3376 (IGMPv2+IGMPv3) require the multicast link layer
-	 * all-systems destination addresses (224.0.0.1) for general queries
-	 */
-	if (!group && iph->daddr != htonl(INADDR_ALLHOSTS_GROUP)) {
-		err = -EINVAL;
+	} else {
 		goto out;
 	}
 
@@ -1329,12 +1315,6 @@ static int br_ip6_multicast_query(struct net_bridge *br,
 	    (port && port->state == BR_STATE_DISABLED))
 		goto out;
 
-	/* RFC2710+RFC3810 (MLDv1+MLDv2) require link-local source addresses */
-	if (!(ipv6_addr_type(&ip6h->saddr) & IPV6_ADDR_LINKLOCAL)) {
-		err = -EINVAL;
-		goto out;
-	}
-
 	if (skb->len == sizeof(*mld)) {
 		if (!pskb_may_pull(skb, sizeof(*mld))) {
 			err = -EINVAL;
@@ -1358,14 +1338,6 @@ static int br_ip6_multicast_query(struct net_bridge *br,
 
 	is_general_query = group && ipv6_addr_any(group);
 
-	/* RFC2710+RFC3810 (MLDv1+MLDv2) require the multicast link layer
-	 * all-nodes destination address (ff02::1) for general queries
-	 */
-	if (is_general_query &&
!ipv6_addr_is_ll_all_nodes(&ip6h->daddr)) {
-		err = -EINVAL;
-		goto out;
-	}
-
 	if (is_general_query) {
 		saddr.proto = htons(ETH_P_IPV6);
 		saddr.u.ip6 = ip6h->saddr;
@@ -1557,66 +1529,22 @@ static int br_multicast_ipv4_rcv(struct net_bridge *br,
 				 struct sk_buff *skb,
 				 u16 vid)
 {
-	struct sk_buff *skb2 = skb;
-	const struct iphdr *iph;
+	struct sk_buff *skb_trimmed = NULL;
 	struct igmphdr *ih;
-	unsigned int len;
-	unsigned int offset;
 	int err;
 
-	/* We treat OOM as packet loss for now. */
-	if (!pskb_may_pull(skb, sizeof(*iph)))
-		return -EINVAL;
-
-	iph = ip_hdr(skb);
-
-	if (iph->ihl < 5 || iph->version != 4)
-		return -EINVAL;
-
-	if (!pskb_may_pull(skb, ip_hdrlen(skb)))
-		return -EINVAL;
-
-	iph = ip_hdr(skb);
+	err = ip_mc_check_igmp(skb, &skb_trimmed);
 
-	if (unlikely(ip_fast_csum((u8 *)iph, iph->ihl)))
-		return -EINVAL;
-
-	if (iph->protocol != IPPROTO_IGMP) {
-		if (!ipv4_is_local_multicast(iph->daddr))
+	if (err == -ENOMSG) {
+		if (!ipv4_is_local_multicast(ip_hdr(skb)->daddr))
 			BR_INPUT_SKB_CB(skb)->mrouters_only = 1;
 		return 0;
+	} else if (err < 0) {
+		return err;
 	}
 
-	len = ntohs(iph->tot_len);
-	if (skb->len < len || len < ip_hdrlen(skb))
-		return -EINVAL;
-
-	if (skb->len > len) {
-		skb2 = skb_clone(skb, GFP_ATOMIC);
-		if (!skb2)
-			return -ENOMEM;
-
-		err = pskb_trim_rcsum(skb2, len);
-		if (err)
-			goto err_out;
-	}
-
-	len -= ip_hdrlen(skb2);
-	offset = skb_network_offset(skb2) + ip_hdrlen(skb2);
-	__skb_pull(skb2, offset);
-	skb_reset_transport_header(skb2);
-
-	err = -EINVAL;
-	if (!pskb_may_pull(skb2, sizeof(*ih)))
-		goto out;
-
-	if (skb_checksum_simple_validate(skb2))
-		goto out;
-
-	err = 0;
-
 	BR_INPUT_SKB_CB(skb)->igmp = 1;
-	ih = igmp_hdr(skb2);
+	ih = igmp_hdr(skb);
 
 	switch (ih->type) {
 	case IGMP_HOST_MEMBERSHIP_REPORT:
@@ -1625,21 +1553,19 @@ static int br_multicast_ipv4_rcv(struct net_bridge *br,
 		err = br_ip4_multicast_add_group(br, port, ih->group, vid);
 		break;
 	case IGMPV3_HOST_MEMBERSHIP_REPORT:
-		err = br_ip4_multicast_igmp3_report(br, port, skb2, vid);
+		err = br_ip4_multicast_igmp3_report(br, port, skb_trimmed, vid);
 		break;
 	case IGMP_HOST_MEMBERSHIP_QUERY:
-		err = br_ip4_multicast_query(br, port, skb2, vid);
+		err = br_ip4_multicast_query(br, port, skb_trimmed, vid);
 		break;
 	case IGMP_HOST_LEAVE_MESSAGE:
 		br_ip4_multicast_leave_group(br, port, ih->group, vid);
 		break;
 	}
 
-out:
-	__skb_push(skb2, offset);
-err_out:
-	if (skb2 != skb)
-		kfree_skb(skb2);
+	if (skb_trimmed)
+		kfree_skb(skb_trimmed);
+
 	return err;
 }
 
@@ -1649,126 +1575,42 @@ static int br_multicast_ipv6_rcv(struct net_bridge *br,
 				 struct sk_buff *skb,
 				 u16 vid)
 {
-	struct sk_buff *skb2;
-	const struct ipv6hdr *ip6h;
-	u8 icmp6_type;
-	u8 nexthdr;
-	__be16 frag_off;
-	unsigned int len;
-	int offset;
+	struct sk_buff *skb_trimmed = NULL;
+	struct mld_msg *mld;
 	int err;
 
-	if (!pskb_may_pull(skb, sizeof(*ip6h)))
-		return -EINVAL;
+	err = ipv6_mc_check_mld(skb, &skb_trimmed);
 
-	ip6h = ipv6_hdr(skb);
-
-	/*
-	 * We're interested in MLD messages only.
-	 *  - Version is 6
-	 *  - MLD has always Router Alert hop-by-hop option
-	 *  - But we do not support jumbrograms.
-	 */
-	if (ip6h->version != 6)
-		return 0;
-
-	/* Prevent flooding this packet if there is no listener present */
-	if (!ipv6_addr_is_ll_all_nodes(&ip6h->daddr))
-		BR_INPUT_SKB_CB(skb)->mrouters_only = 1;
-
-	if (ip6h->nexthdr != IPPROTO_HOPOPTS ||
-	    ip6h->payload_len == 0)
-		return 0;
-
-	len = ntohs(ip6h->payload_len) + sizeof(*ip6h);
-	if (skb->len < len)
-		return -EINVAL;
-
-	nexthdr = ip6h->nexthdr;
-	offset = ipv6_skip_exthdr(skb, sizeof(*ip6h), &nexthdr, &frag_off);
-
-	if (offset < 0 || nexthdr != IPPROTO_ICMPV6)
+	if (err == -ENOMSG) {
+		if (!ipv6_addr_is_ll_all_nodes(&ipv6_hdr(skb)->daddr))
+			BR_INPUT_SKB_CB(skb)->mrouters_only = 1;
 		return 0;
-
-	/* Okay, we found ICMPv6 header */
-	skb2 = skb_clone(skb, GFP_ATOMIC);
-	if (!skb2)
-		return -ENOMEM;
-
-	err = -EINVAL;
-	if (!pskb_may_pull(skb2, offset + sizeof(struct icmp6hdr)))
-		goto out;
-
-	len -= offset - skb_network_offset(skb2);
-
-	__skb_pull(skb2, offset);
-	skb_reset_transport_header(skb2);
-	skb_postpull_rcsum(skb2, skb_network_header(skb2),
-			   skb_network_header_len(skb2));
-
-	icmp6_type = icmp6_hdr(skb2)->icmp6_type;
-
-	switch (icmp6_type) {
-	case ICMPV6_MGM_QUERY:
-	case ICMPV6_MGM_REPORT:
-	case ICMPV6_MGM_REDUCTION:
-	case ICMPV6_MLD2_REPORT:
-		break;
-	default:
-		err = 0;
-		goto out;
-	}
-
-	/* Okay, we found MLD message. Check further. */
-	if (skb2->len > len) {
-		err = pskb_trim_rcsum(skb2, len);
-		if (err)
-			goto out;
-		err = -EINVAL;
+	} else if (err < 0) {
+		return err;
 	}
 
-	ip6h = ipv6_hdr(skb2);
-
-	if (skb_checksum_validate(skb2, IPPROTO_ICMPV6, ip6_compute_pseudo))
-		goto out;
-
-	err = 0;
-
 	BR_INPUT_SKB_CB(skb)->igmp = 1;
+	mld = (struct mld_msg *)skb_transport_header(skb);
 
-	switch (icmp6_type) {
+	switch (mld->mld_type) {
 	case ICMPV6_MGM_REPORT:
-	    {
-		struct mld_msg *mld;
-		if (!pskb_may_pull(skb2, sizeof(*mld))) {
-			err = -EINVAL;
-			goto out;
-		}
-		mld = (struct mld_msg *)skb_transport_header(skb2);
 		BR_INPUT_SKB_CB(skb)->mrouters_only = 1;
 		err = br_ip6_multicast_add_group(br, port, &mld->mld_mca, vid);
 		break;
-	    }
 	case ICMPV6_MLD2_REPORT:
-		err = br_ip6_multicast_mld2_report(br, port, skb2, vid);
+		err = br_ip6_multicast_mld2_report(br, port, skb_trimmed, vid);
 		break;
 	case ICMPV6_MGM_QUERY:
-		err = br_ip6_multicast_query(br, port, skb2, vid);
+		err = br_ip6_multicast_query(br, port, skb_trimmed, vid);
 		break;
 	case ICMPV6_MGM_REDUCTION:
-	    {
-		struct mld_msg *mld;
-		if (!pskb_may_pull(skb2, sizeof(*mld))) {
-			err = -EINVAL;
-			goto out;
-		}
-		mld = (struct mld_msg *)skb_transport_header(skb2);
 		br_ip6_multicast_leave_group(br, port, &mld->mld_mca, vid);
-	    }
+		break;
 	}
 
-out:
-	kfree_skb(skb2);
+	if (skb_trimmed)
+		kfree_skb(skb_trimmed);
+
 	return err;
 }
 #endif
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 3cfff2a..1e4278a 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4030,6 +4030,93 @@ int skb_checksum_setup(struct sk_buff *skb, bool
recalculate)
 }
 EXPORT_SYMBOL(skb_checksum_setup);
 
+/**
+ * skb_checksum_maybe_trim - maybe trims the given skb
+ * @skb: the skb to check
+ * @transport_len: the data length beyond the network header
+ *
+ * Checks whether the given skb has data beyond the given transport length.
+ * If so, returns a cloned skb trimmed to this transport length.
+ * Otherwise returns the provided skb. Returns NULL in error cases
+ * (e.g. transport_len exceeds skb length or out-of-memory).
+ *
+ * Caller needs to set the skb transport header and release the returned skb.
+ * Provided skb is consumed.
+ */
+static struct sk_buff *skb_checksum_maybe_trim(struct sk_buff *skb,
+					       unsigned int transport_len)
+{
+	struct sk_buff *skb_chk;
+	unsigned int len = skb_transport_offset(skb) + transport_len;
+	int ret;
+
+	if (skb->len < len) {
+		kfree_skb(skb);
+		return NULL;
+	} else if (skb->len == len) {
+		return skb;
+	}
+
+	skb_chk = skb_clone(skb, GFP_ATOMIC);
+	kfree_skb(skb);
+
+	if (!skb_chk)
+		return NULL;
+
+	ret = pskb_trim_rcsum(skb_chk, len);
+	if (ret) {
+		kfree_skb(skb_chk);
+		return NULL;
+	}
+
+	return skb_chk;
+}
+
+/**
+ * skb_checksum_trimmed - validate checksum of an skb
+ * @skb: the skb to check
+ * @transport_len: the data length beyond the network header
+ * @skb_chkf: checksum function to use
+ *
+ * Applies the given checksum function skb_chkf to the provided skb.
+ * Returns a checked and maybe trimmed skb. Returns NULL on error.
+ *
+ * If the skb has data beyond the given transport length, then a
+ * trimmed & cloned skb is checked and returned.
+ *
+ * Caller needs to set the skb transport header and release the returned skb.
+ * Provided skb is consumed.
+ */
+struct sk_buff *skb_checksum_trimmed(struct sk_buff *skb,
+				     unsigned int transport_len,
+				     __sum16(*skb_chkf)(struct sk_buff *skb))
+{
+	struct sk_buff *skb_chk;
+	unsigned int offset = skb_transport_offset(skb);
+	int ret;
+
+	skb_chk = skb_checksum_maybe_trim(skb, transport_len);
+	if (!skb_chk)
+		return NULL;
+
+	if (!pskb_may_pull(skb_chk, offset)) {
+		kfree_skb(skb_chk);
+		return NULL;
+	}
+
+	__skb_pull(skb_chk, offset);
+	ret = skb_chkf(skb_chk);
+	__skb_push(skb_chk, offset);
+
+	if (ret) {
+		kfree_skb(skb_chk);
+		return NULL;
+	}
+
+	return skb_chk;
+}
+EXPORT_SYMBOL(skb_checksum_trimmed);
+
 void __skb_warn_lro_forwarding(const struct sk_buff *skb)
 {
 	net_warn_ratelimited("%s: received packets cannot be forwarded while LRO
is enabled\n",
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index a3a697f..651cdf6 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -1339,6 +1339,168 @@ out:
 }
 EXPORT_SYMBOL(ip_mc_inc_group);
 
+static int ip_mc_check_iphdr(struct sk_buff *skb)
+{
+	const struct iphdr *iph;
+	unsigned int len;
+	unsigned int offset = skb_network_offset(skb) + sizeof(*iph);
+
+	if (!pskb_may_pull(skb, offset))
+		return -EINVAL;
+
+	iph = ip_hdr(skb);
+
+	if (iph->version != 4 || ip_hdrlen(skb) < sizeof(*iph))
+		return -EINVAL;
+
+	offset += ip_hdrlen(skb) - sizeof(*iph);
+
+	if (!pskb_may_pull(skb, offset))
+		return -EINVAL;
+
+	iph = ip_hdr(skb);
+
+	if (unlikely(ip_fast_csum((u8 *)iph, iph->ihl)))
+		return -EINVAL;
+
+	len = skb_network_offset(skb) + ntohs(iph->tot_len);
+	if (skb->len < len || len < offset)
+		return -EINVAL;
+
+	skb_set_transport_header(skb, offset);
+
+	return 0;
+}
+
+static int ip_mc_check_igmp_reportv3(struct sk_buff *skb)
+{
+	unsigned int len = skb_transport_offset(skb);
+
+	len += sizeof(struct igmpv3_report);
+
+	return pskb_may_pull(skb, len) ? 0 : -EINVAL;
+}
+
+static int ip_mc_check_igmp_query(struct sk_buff *skb)
+{
+	unsigned int len = skb_transport_offset(skb);
+
+	len += sizeof(struct igmphdr);
+	if (skb->len < len)
+		return -EINVAL;
+
+	/* IGMPv{1,2}? */
+	if (skb->len != len) {
+		/* or IGMPv3? */
+		len += sizeof(struct igmpv3_query) - sizeof(struct igmphdr);
+		if (skb->len < len || !pskb_may_pull(skb, len))
+			return -EINVAL;
+	}
+
+	/* RFC2236+RFC3376 (IGMPv2+IGMPv3) require the multicast link layer
+	 * all-systems destination addresses (224.0.0.1) for general queries
+	 */
+	if (!igmp_hdr(skb)->group &&
+	    ip_hdr(skb)->daddr != htonl(INADDR_ALLHOSTS_GROUP))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int ip_mc_check_igmp_msg(struct sk_buff *skb)
+{
+	switch (igmp_hdr(skb)->type) {
+	case IGMP_HOST_LEAVE_MESSAGE:
+	case IGMP_HOST_MEMBERSHIP_REPORT:
+	case IGMPV2_HOST_MEMBERSHIP_REPORT:
+		/* fall through */
+		return 0;
+	case IGMPV3_HOST_MEMBERSHIP_REPORT:
+		return ip_mc_check_igmp_reportv3(skb);
+	case IGMP_HOST_MEMBERSHIP_QUERY:
+		return ip_mc_check_igmp_query(skb);
+	default:
+		return -ENOMSG;
+	}
+}
+
+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)
+
+{
+	struct sk_buff *skb_chk;
+	unsigned int transport_len;
+	unsigned int len = skb_transport_offset(skb) + sizeof(struct igmphdr);
+	int ret;
+
+	transport_len = ntohs(ip_hdr(skb)->tot_len) - ip_hdrlen(skb);
+
+	skb_get(skb);
+	skb_chk = skb_checksum_trimmed(skb, transport_len,
+				       ip_mc_validate_checksum);
+	if (!skb_chk)
+		return -EINVAL;
+
+	if (!pskb_may_pull(skb_chk, len)) {
+		kfree_skb(skb_chk);
+		return -EINVAL;
+	}
+
+	ret = ip_mc_check_igmp_msg(skb_chk);
+	if (ret) {
+		kfree_skb(skb_chk);
+		return ret;
+	}
+
+	if (skb_trimmed)
+		*skb_trimmed = skb_chk;
+	else
+		kfree_skb(skb_chk);
+
+	return 0;
+}
+
+/**
+ * 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 network and transport headers accordingly and returns zero.
+ *
+ * -EINVAL: A broken packet was detected, i.e. it violates some internet
+ *  standard
+ * -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).
+ *
+ * The caller needs to release a reference count from any returned skb_trimmed.
+ */
+int ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed)
+{
+	int ret = ip_mc_check_iphdr(skb);
+
+	if (ret < 0)
+		return ret;
+
+	if (ip_hdr(skb)->protocol != IPPROTO_IGMP)
+		return -ENOMSG;
+
+	return __ip_mc_check_igmp(skb, skb_trimmed);
+}
+EXPORT_SYMBOL(ip_mc_check_igmp);
+
 /*
  *	Resend IGMP JOIN report; used by netdev notifier.
  */
diff --git a/net/ipv6/Makefile b/net/ipv6/Makefile
index 2e8c061..0f3f199 100644
--- a/net/ipv6/Makefile
+++ b/net/ipv6/Makefile
@@ -48,4 +48,5 @@ obj-$(subst m,y,$(CONFIG_IPV6)) += inet6_hashtables.o
 
 ifneq ($(CONFIG_IPV6),)
 obj-$(CONFIG_NET_UDP_TUNNEL) += ip6_udp_tunnel.o
+obj-y += mcast_snoop.o
 endif
diff --git a/net/ipv6/mcast_snoop.c b/net/ipv6/mcast_snoop.c
new file mode 100644
index 0000000..1a2cbc1
--- /dev/null
+++ b/net/ipv6/mcast_snoop.c
@@ -0,0 +1,213 @@
+/* Copyright (C) 2010: YOSHIFUJI Hideaki <yoshfuji at linux-ipv6.org>
+ * Copyright (C) 2015: Linus L?ssing <linus.luessing at c0d3.blue>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ *
+ *
+ * Based on the MLD support added to br_multicast.c by YOSHIFUJI Hideaki.
+ */
+
+#include <linux/skbuff.h>
+#include <net/ipv6.h>
+#include <net/mld.h>
+#include <net/addrconf.h>
+#include <net/ip6_checksum.h>
+
+static int ipv6_mc_check_ip6hdr(struct sk_buff *skb)
+{
+	const struct ipv6hdr *ip6h;
+	unsigned int len;
+	unsigned int offset = skb_network_offset(skb) + sizeof(*ip6h);
+
+	if (!pskb_may_pull(skb, offset))
+		return -EINVAL;
+
+	ip6h = ipv6_hdr(skb);
+
+	if (ip6h->version != 6)
+		return -EINVAL;
+
+	len = offset + ntohs(ip6h->payload_len);
+	if (skb->len < len || len <= offset)
+		return -EINVAL;
+
+	return 0;
+}
+
+static int ipv6_mc_check_exthdrs(struct sk_buff *skb)
+{
+	const struct ipv6hdr *ip6h;
+	unsigned int offset;
+	u8 nexthdr;
+	__be16 frag_off;
+
+	ip6h = ipv6_hdr(skb);
+
+	if (ip6h->nexthdr != IPPROTO_HOPOPTS)
+		return -ENOMSG;
+
+	nexthdr = ip6h->nexthdr;
+	offset = skb_network_offset(skb) + sizeof(*ip6h);
+	offset = ipv6_skip_exthdr(skb, offset, &nexthdr, &frag_off);
+
+	if (offset < 0)
+		return -EINVAL;
+
+	if (nexthdr != IPPROTO_ICMPV6)
+		return -ENOMSG;
+
+	skb_set_transport_header(skb, offset);
+
+	return 0;
+}
+
+static int ipv6_mc_check_mld_reportv2(struct sk_buff *skb)
+{
+	unsigned int len = skb_transport_offset(skb);
+
+	len += sizeof(struct mld2_report);
+
+	return pskb_may_pull(skb, len) ? 0 : -EINVAL;
+}
+
+static int ipv6_mc_check_mld_query(struct sk_buff *skb)
+{
+	struct mld_msg *mld;
+	unsigned int len = skb_transport_offset(skb);
+
+	/* RFC2710+RFC3810 (MLDv1+MLDv2) require link-local source addresses */
+	if (!(ipv6_addr_type(&ipv6_hdr(skb)->saddr) & IPV6_ADDR_LINKLOCAL))
+		return -EINVAL;
+
+	len += sizeof(struct mld_msg);
+	if (skb->len < len)
+		return -EINVAL;
+
+	/* MLDv1? */
+	if (skb->len != len) {
+		/* or MLDv2? */
+		len += sizeof(struct mld2_query) - sizeof(struct mld_msg);
+		if (skb->len < len || !pskb_may_pull(skb, len))
+			return -EINVAL;
+	}
+
+	mld = (struct mld_msg *)skb_transport_header(skb);
+
+	/* RFC2710+RFC3810 (MLDv1+MLDv2) require the multicast link layer
+	 * all-nodes destination address (ff02::1) for general queries
+	 */
+	if (ipv6_addr_any(&mld->mld_mca) &&
+	    !ipv6_addr_is_ll_all_nodes(&ipv6_hdr(skb)->daddr))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int ipv6_mc_check_mld_msg(struct sk_buff *skb)
+{
+	struct mld_msg *mld = (struct mld_msg *)skb_transport_header(skb);
+
+	switch (mld->mld_type) {
+	case ICMPV6_MGM_REDUCTION:
+	case ICMPV6_MGM_REPORT:
+		/* fall through */
+		return 0;
+	case ICMPV6_MLD2_REPORT:
+		return ipv6_mc_check_mld_reportv2(skb);
+	case ICMPV6_MGM_QUERY:
+		return ipv6_mc_check_mld_query(skb);
+	default:
+		return -ENOMSG;
+	}
+}
+
+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)
+
+{
+	struct sk_buff *skb_chk = NULL;
+	unsigned int transport_len;
+	unsigned int len = skb_transport_offset(skb) + sizeof(struct mld_msg);
+	int ret;
+
+	transport_len = ntohs(ipv6_hdr(skb)->payload_len);
+	transport_len -= skb_transport_offset(skb) - sizeof(struct ipv6hdr);
+
+	skb_get(skb);
+	skb_chk = skb_checksum_trimmed(skb, transport_len,
+				       ipv6_mc_validate_checksum);
+	if (!skb_chk)
+		return -EINVAL;
+
+	if (!pskb_may_pull(skb_chk, len)) {
+		kfree_skb(skb_chk);
+		return -EINVAL;
+	}
+
+	ret = ipv6_mc_check_mld_msg(skb_chk);
+	if (ret) {
+		kfree_skb(skb_chk);
+		return ret;
+	}
+
+	if (skb_trimmed)
+		*skb_trimmed = skb_chk;
+	else
+		kfree_skb(skb_chk);
+
+	return 0;
+}
+
+/**
+ * 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 network and transport headers accordingly and returns zero.
+ *
+ * -EINVAL: A broken packet was detected, i.e. it violates some internet
+ *  standard
+ * -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).
+ *
+ * The caller needs to release a reference count from any returned skb_trimmed.
+ */
+int ipv6_mc_check_mld(struct sk_buff *skb, struct sk_buff **skb_trimmed)
+{
+	int ret;
+
+	ret = ipv6_mc_check_ip6hdr(skb);
+	if (ret < 0)
+		return ret;
+
+	ret = ipv6_mc_check_exthdrs(skb);
+	if (ret < 0)
+		return ret;
+
+	return __ipv6_mc_check_mld(skb, skb_trimmed);
+}
+EXPORT_SYMBOL(ipv6_mc_check_mld);
-- 
1.7.10.4

From: Linus L?ssing <linus.luessing at c0d3.blue>
Date: Sat,  2 May 2015 14:01:05 +0200
> The multicast optimizations in batman-adv are yet only usable and
> enabled in non-bridged scenarios. To be able to support bridged setups
> batman-adv needs to be able to detect IGMP/MLD queriers and reports on
> mesh nodes without bridges, too. See the following link for details:
> 
>
http://www.open-mesh.org/projects/batman-adv/wiki/Multicast-optimizations-listener-reports
> 
> To avoid duplicate code between the bridge and batman-adv, the IGMP/MLD
> message validation code is moved from the bridge to the IPv4/IPv6 stack.
> 
> On the way, some refactoring to increase readability and to iron out
> some subtle differences between the IGMP and MLD parsing code is done.
Series applied, thanks.