net: Export IGMP/MLD message validation code

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

1 files changed, 162 insertions, 0 deletions

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index a3a697f5ffba..651cdf648ec4 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.
  */