diff mbox series

[v3,1/2] batman-adv: Snoop DHCPACKs for DAT

Message ID 20180507013823.739-2-linus.luessing@c0d3.blue
State Superseded, archived
Delegated to: Simon Wunderlich
Headers show
Series batman-adv: DHCP snooping for DAT | expand

Commit Message

Linus Lüssing May 7, 2018, 1:38 a.m. UTC
In a 1000 nodes mesh network (Freifunk Hamburg) we can still see
30KBit/s of ARP traffic (equalling about 25% of all layer two
specific overhead, remaining after some filtering) flooded through
the mesh. These 30KBit/s are mainly ARP Requests from the
gateways / DHCP servers.

By snooping DHCPACKs we can learn about MAC/IP address pairs
in the DHCP range without relying on ARP. This eliminates the need
for mesh wide message flooding for IPv4 address resolution.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
---
Changes in v3:
* Rebase to master
* Shortened commit message

Changes in v2:
* Rebase to master
* Fix compilation with CONFIG_BATMAN_ADV=n (added stubs)

Changes in RFC -> non-RFC

 * Added kerneldoc
 * Added Signed-off-by
 * More IP Header checks
   (iph->hlen considered, ip version checked, ...)
 * Parsing & checking DHCP Message Type Option,
   only snooping DHCPACKs now
 * Moved ethernet protocol check from batadv_dat_check_dhcp to
   batadv_dat_check_dhcp_ipudp
 * Removed buffer-length parameter from
   batadv_dat_dhcp_get_{yiaddr,chaddr}()
 * Renamed batadv_dat_put() to batadv_dat_put_pairs()
---
 include/uapi/linux/batadv_packet.h     |  48 ++++++
 net/batman-adv/distributed-arp-table.c | 296 +++++++++++++++++++++++++++++++++
 net/batman-adv/distributed-arp-table.h |  11 ++
 net/batman-adv/soft-interface.c        |  11 +-
 4 files changed, 364 insertions(+), 2 deletions(-)

Comments

Marek Lindner May 12, 2018, 10:26 p.m. UTC | #1
On Monday, May 7, 2018 9:38:22 AM HKT Linus Lüssing wrote:
>  include/uapi/linux/batadv_packet.h     |  48 ++++++
>  net/batman-adv/distributed-arp-table.c | 296
> +++++++++++++++++++++++++++++++++ net/batman-adv/distributed-arp-table.h | 
> 11 ++
>  net/batman-adv/soft-interface.c        |  11 +-
>  4 files changed, 364 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/batadv_packet.h
> b/include/uapi/linux/batadv_packet.h index 894d8d2f..7ef7b519 100644
> --- a/include/uapi/linux/batadv_packet.h
> +++ b/include/uapi/linux/batadv_packet.h
> @@ -630,6 +630,54 @@ struct batadv_tvlv_mcast_data {
>         __u8 reserved[3];
>  };
> 
> +enum batadv_bootpop {
> +       BATADV_BOOTREQUEST      = 1,
> +       BATADV_BOOTREPLY        = 2,
> +};
> +
> +enum batadv_boothtype {
> +       BATADV_HTYPE_ETHERNET   = 1,
> +};
> +
> +enum batadv_dhcpoptioncode {
> +       BATADV_DHCP_OPT_PAD             = 0,
> +       BATADV_DHCP_OPT_MSG_TYPE        = 53,
> +       BATADV_DHCP_OPT_END             = 255,
> +};
> +
> +enum batadv_dhcptype {
> +       BATADV_DHCPDISCOVER     = 1,
> +       BATADV_DHCPOFFER        = 2,
> +       BATADV_DHCPREQUEST      = 3,
> +       BATADV_DHCPDECLINE      = 4,
> +       BATADV_DHCPACK          = 5,
> +       BATADV_DHCPNAK          = 6,
> +       BATADV_DHCPRELEASE      = 7,
> +       BATADV_DHCPINFORM       = 8,
> +};

Can we shorten these definitions by only listing those that are used by the 
code below ?


> @@ -1130,6 +1133,7 @@ batadv_dat_arp_create_reply(struct batadv_priv
> *bat_priv, __be32 ip_src, return NULL;
> 
>         skb_reset_mac_header(skb);
> +       skb_set_network_header(skb, ETH_HLEN);
> 
>         if (vid & BATADV_VLAN_HAS_TAG)
>                 skb = vlan_insert_tag(skb, htons(ETH_P_8021Q),

Might be better to move the skb_set_network_header() call into 
batadv_dat_put_pairs() where it is needed by skb_network_offset() ?

Cheers,
Marek
diff mbox series

Patch

diff --git a/include/uapi/linux/batadv_packet.h b/include/uapi/linux/batadv_packet.h
index 894d8d2f..7ef7b519 100644
--- a/include/uapi/linux/batadv_packet.h
+++ b/include/uapi/linux/batadv_packet.h
@@ -630,6 +630,54 @@  struct batadv_tvlv_mcast_data {
 	__u8 reserved[3];
 };
 
+enum batadv_bootpop {
+	BATADV_BOOTREQUEST	= 1,
+	BATADV_BOOTREPLY	= 2,
+};
+
+enum batadv_boothtype {
+	BATADV_HTYPE_ETHERNET	= 1,
+};
+
+enum batadv_dhcpoptioncode {
+	BATADV_DHCP_OPT_PAD		= 0,
+	BATADV_DHCP_OPT_MSG_TYPE	= 53,
+	BATADV_DHCP_OPT_END		= 255,
+};
+
+enum batadv_dhcptype {
+	BATADV_DHCPDISCOVER	= 1,
+	BATADV_DHCPOFFER	= 2,
+	BATADV_DHCPREQUEST	= 3,
+	BATADV_DHCPDECLINE	= 4,
+	BATADV_DHCPACK		= 5,
+	BATADV_DHCPNAK		= 6,
+	BATADV_DHCPRELEASE	= 7,
+	BATADV_DHCPINFORM	= 8,
+};
+
+/* { 99, 130, 83, 99 } */
+#define BATADV_DHCP_MAGIC 1669485411
+
+struct batadv_dhcp_packet {
+	__u8 op;
+	__u8 htype;
+	__u8 hlen;
+	__u8 hops;
+	__be32 xid;
+	__be16 secs;
+	__be16 flags;
+	__be32 ciaddr;
+	__be32 yiaddr;
+	__be32 siaddr;
+	__be32 giaddr;
+	__u8 chaddr[16];
+	__u8 sname[64];
+	__u8 file[128];
+	__be32 magic;
+	__u8 options[0];
+};
+
 #pragma pack()
 
 #endif /* _UAPI_LINUX_BATADV_PACKET_H_ */
diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c
index a60bacf7..00b96379 100644
--- a/net/batman-adv/distributed-arp-table.c
+++ b/net/batman-adv/distributed-arp-table.c
@@ -29,6 +29,7 @@ 
 #include <linux/if_ether.h>
 #include <linux/if_vlan.h>
 #include <linux/in.h>
+#include <linux/ip.h>
 #include <linux/jiffies.h>
 #include <linux/kernel.h>
 #include <linux/kref.h>
@@ -42,9 +43,11 @@ 
 #include <linux/spinlock.h>
 #include <linux/stddef.h>
 #include <linux/string.h>
+#include <linux/udp.h>
 #include <linux/workqueue.h>
 #include <net/arp.h>
 #include <net/genetlink.h>
+#include <net/ip.h>
 #include <net/netlink.h>
 #include <net/sock.h>
 #include <uapi/linux/batman_adv.h>
@@ -1130,6 +1133,7 @@  batadv_dat_arp_create_reply(struct batadv_priv *bat_priv, __be32 ip_src,
 		return NULL;
 
 	skb_reset_mac_header(skb);
+	skb_set_network_header(skb, ETH_HLEN);
 
 	if (vid & BATADV_VLAN_HAS_TAG)
 		skb = vlan_insert_tag(skb, htons(ETH_P_8021Q),
@@ -1436,6 +1440,298 @@  bool batadv_dat_snoop_incoming_arp_reply(struct batadv_priv *bat_priv,
 }
 
 /**
+ * batadv_dat_check_dhcp_ipudp() - check skb for IP+UDP headers valid for DHCP
+ * @skb: the packet to check
+ * @proto: ethernet protocol hint (behind a potential vlan)
+ *
+ * Checks whether the given skb has an IP and UDP header valid for a DHCP
+ * message from a DHCP server.
+ *
+ * Return: True if valid, false otherwise.
+ */
+static bool batadv_dat_check_dhcp_ipudp(struct sk_buff *skb)
+{
+	struct iphdr *iphdr, _iphdr;
+	struct udphdr *udphdr, _udphdr;
+	unsigned int offset = skb_network_offset(skb);
+
+	iphdr = skb_header_pointer(skb, offset, sizeof(_iphdr), &_iphdr);
+	if (!iphdr || iphdr->version != 4 || ip_hdrlen(skb) < sizeof(_iphdr))
+		return false;
+
+	if (iphdr->protocol != IPPROTO_UDP)
+		return false;
+
+	offset += ip_hdrlen(skb);
+	skb_set_transport_header(skb, offset);
+
+	udphdr = skb_header_pointer(skb, offset, sizeof(_udphdr), &_udphdr);
+	if (!udphdr || udphdr->source != htons(67))
+		return false;
+
+	return true;
+}
+
+/**
+ * batadv_dat_check_dhcp() - examine packet for valid DHCP message
+ * @skb: the packet to check
+ * @proto: ethernet protocol hint (behind a potential vlan)
+ *
+ * Checks whether the given skb is a valid DHCP packet.
+ *
+ * Caller needs to ensure that the skb network header is set correctly.
+ *
+ * Return: If skb is a valid DHCP packet, then returns its op code
+ * (e.g. BOOTREPLY vs. BOOTREQUEST). Otherwise returns -EINVAL.
+ */
+static int batadv_dat_check_dhcp(struct sk_buff *skb, __be16 proto)
+{
+	u8 *op, _op;
+	u8 *htype, _htype;
+	u8 *hlen, _hlen;
+	__be32 *magic, _magic;
+	unsigned int dhcp_offset;
+	unsigned int offset;
+
+	if (proto != htons(ETH_P_IP))
+		return -EINVAL;
+
+	if (!batadv_dat_check_dhcp_ipudp(skb))
+		return -EINVAL;
+
+	dhcp_offset = skb_transport_offset(skb) + sizeof(struct udphdr);
+	if (skb->len < dhcp_offset + sizeof(struct batadv_dhcp_packet))
+		return -EINVAL;
+
+	offset = dhcp_offset + offsetof(struct batadv_dhcp_packet, op);
+
+	op = skb_header_pointer(skb, offset, sizeof(_op), &_op);
+	if (!op)
+		return -EINVAL;
+
+	offset = dhcp_offset + offsetof(struct batadv_dhcp_packet, htype);
+
+	htype = skb_header_pointer(skb, offset, sizeof(_htype), &_htype);
+	if (!htype || *htype != BATADV_HTYPE_ETHERNET)
+		return -EINVAL;
+
+	offset = dhcp_offset + offsetof(struct batadv_dhcp_packet, hlen);
+
+	hlen = skb_header_pointer(skb, offset, sizeof(_hlen), &_hlen);
+	if (!hlen || *hlen != ETH_ALEN)
+		return -EINVAL;
+
+	offset = dhcp_offset + offsetof(struct batadv_dhcp_packet, magic);
+
+	magic = skb_header_pointer(skb, offset, sizeof(_magic), &_magic);
+	if (!magic || *magic != htonl(BATADV_DHCP_MAGIC))
+		return -EINVAL;
+
+	return *op;
+}
+
+/**
+ * batadv_dat_get_dhcp_message_type() - get message type of a DHCP packet
+ * @skb: the DHCP packet to parse
+ *
+ * Iterates over the DHCP options of the given DHCP packet to find a
+ * DHCP Message Type option and parse it.
+ *
+ * Caller needs to ensure that the given skb is a valid DHCP packet and
+ * that the skb transport header is set correctly.
+ *
+ * Return: The found DHCP message type value, if found. -EINVAL otherwise.
+ */
+static int batadv_dat_get_dhcp_message_type(struct sk_buff *skb)
+{
+	unsigned int offset = skb_transport_offset(skb) + sizeof(struct udphdr);
+	u8 *type, _type;
+	struct {
+		u8 type;
+		u8 len;
+	} *tl, _tl;
+
+	offset += sizeof(struct batadv_dhcp_packet);
+
+	while ((tl = skb_header_pointer(skb, offset, sizeof(_tl), &_tl))) {
+		if (tl->type == BATADV_DHCP_OPT_MSG_TYPE)
+			break;
+
+		if (tl->type == BATADV_DHCP_OPT_END)
+			break;
+
+		if (tl->type == BATADV_DHCP_OPT_PAD)
+			offset++;
+		else
+			offset += tl->len + sizeof(_tl);
+	}
+
+	/* Option Overload Code not supported */
+	if (!tl || tl->type != BATADV_DHCP_OPT_MSG_TYPE ||
+	    tl->len != sizeof(_type))
+		return -EINVAL;
+
+	offset += sizeof(_tl);
+
+	type = skb_header_pointer(skb, offset, sizeof(_type), &_type);
+	if (!type)
+		return -EINVAL;
+
+	return *type;
+}
+
+/**
+ * batadv_dat_get_dhcp_yiaddr() - get yiaddr from a DHCP packet
+ * @skb: the DHCP packet to parse
+ * @buffer: a buffer to store the yiaddr in (if necessary / skb is non-linear)
+ *
+ * Caller needs to ensure that the given skb is a valid DHCP packet and
+ * that the skb transport header is set correctly.
+ *
+ * Return: A safely accessible "Your IP Address" field from the provided DHCP
+ * packet.
+ */
+static __be32 *batadv_dat_dhcp_get_yiaddr(struct sk_buff *skb, __be32 *buffer)
+{
+	unsigned int offset = skb_transport_offset(skb) + sizeof(struct udphdr);
+	unsigned int len = sizeof(((struct batadv_dhcp_packet *)0)->yiaddr);
+
+	offset += offsetof(struct batadv_dhcp_packet, yiaddr);
+
+	return skb_header_pointer(skb, offset, len, buffer);
+}
+
+/**
+ * batadv_dat_get_dhcp_chaddr() - get chaddr from a DHCP packet
+ * @skb: the DHCP packet to parse
+ * @buffer: a buffer to store the chaddr in (if necessary / skb is non-linear)
+ *
+ * Caller needs to ensure that the given skb is a valid DHCP packet and
+ * that the skb transport header is set correctly.
+ *
+ * Return: A safely accessible "Client Hardware Address" field from the provided
+ * DHCP packet.
+ */
+static u8 *batadv_dat_get_dhcp_chaddr(struct sk_buff *skb, u8 *buffer)
+{
+	unsigned int offset = skb_transport_offset(skb) + sizeof(struct udphdr);
+	unsigned int len = sizeof(((struct batadv_dhcp_packet *)0)->chaddr);
+
+	offset += offsetof(struct batadv_dhcp_packet, chaddr);
+
+	return skb_header_pointer(skb, offset, len, buffer);
+}
+
+/**
+ * batadv_dat_put_pairs() - puts two MAC/IP pairs into the DHT and DAT cache
+ * @bat_priv: the bat priv with all the soft interface information
+ * @hw_src: first value of DHT and ARP sender MAC
+ * @ip_src: first key of DHT and ARP sender IP
+ * @hw_dst: second value of DHT and ARP target MAC
+ * @ip_dst: second key of DHT and ARP target IP
+ * @vid: VLAN identifier
+ *
+ * First checks whether the given MAC/IP pairs are suitable for DAT. If so, adds
+ * them to the local DAT cache and propagates them further into the DHT.
+ *
+ * For the DHT propagation, hw_src/ip_src will appear as the ARP Reply
+ * transmitter (and hw_dst/ip_dst as the target).
+ *
+ * Return: True on success, false otherwise.
+ */
+static bool batadv_dat_put_pairs(struct batadv_priv *bat_priv, u8 *hw_src,
+				 __be32 ip_src, u8 *hw_dst, __be32 ip_dst,
+				 unsigned short vid)
+{
+	struct sk_buff *skb;
+	int hdr_size;
+	u16 type;
+	int ret = false;
+
+	skb = batadv_dat_arp_create_reply(bat_priv, ip_src, ip_dst, hw_src,
+					  hw_dst, vid);
+	if (!skb)
+		return false;
+
+	/* Check for validity of provided addresses */
+	hdr_size = skb_network_offset(skb) - ETH_HLEN;
+	type = batadv_arp_get_type(bat_priv, skb, hdr_size);
+	if (type != ARPOP_REPLY)
+		goto err_skip_commit;
+
+	batadv_dat_entry_add(bat_priv, ip_src, hw_src, vid);
+	batadv_dat_entry_add(bat_priv, ip_dst, hw_dst, vid);
+
+	batadv_dat_send_data(bat_priv, skb, ip_src, vid, BATADV_P_DAT_DHT_PUT);
+	batadv_dat_send_data(bat_priv, skb, ip_dst, vid, BATADV_P_DAT_DHT_PUT);
+
+	ret = true;
+
+err_skip_commit:
+	dev_kfree_skb(skb);
+	return ret;
+}
+
+/**
+ * batadv_dat_snoop_outgoing_dhcp_ack() - snoop DHCPACK and fill DAT with it
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the packet to snoop
+ * @proto: ethernet protocol hint (behind a potential vlan)
+ * @vid: VLAN identifier
+ *
+ * This function first checks whether the given skb is a valid DHCPACK. If
+ * so then its source MAC and IP as well as its DHCP Client Hardware Address
+ * field and DHCP Your IP Address field are added to the local DAT cache and
+ * propagated into the DHT.
+ *
+ * Caller needs to ensure that the skb mac and network headers are set
+ * correctly.
+ */
+void batadv_dat_snoop_outgoing_dhcp_ack(struct batadv_priv *bat_priv,
+					struct sk_buff *skb,
+					__be16 proto,
+					unsigned short vid)
+{
+	int type;
+	u8 *chaddr, _chaddr[ETH_ALEN];
+	__be32 *yiaddr, _yiaddr;
+
+	if (!atomic_read(&bat_priv->distributed_arp_table))
+		return;
+
+	if (batadv_dat_check_dhcp(skb, proto) != BATADV_BOOTREPLY)
+		return;
+
+	type = batadv_dat_get_dhcp_message_type(skb);
+	if (type != BATADV_DHCPACK)
+		return;
+
+	yiaddr = batadv_dat_dhcp_get_yiaddr(skb, &_yiaddr);
+	if (!yiaddr)
+		return;
+
+	chaddr = batadv_dat_get_dhcp_chaddr(skb, _chaddr);
+	if (!chaddr)
+		return;
+
+	/* ARP sender MAC + IP -> DHCP Client (chaddr+yiaddr),
+	 * ARP target MAC + IP -> DHCP Server (ethhdr/iphdr sources)
+	 */
+	if (!batadv_dat_put_pairs(bat_priv, chaddr, *yiaddr,
+				  eth_hdr(skb)->h_source, ip_hdr(skb)->saddr,
+				  vid))
+		return;
+
+	batadv_dbg(BATADV_DBG_DAT, bat_priv,
+		   "Snooped from DHCPACK (server-side): %pI4, %pM (vid: %i)\n",
+		   &ip_hdr(skb)->saddr, eth_hdr(skb)->h_source,
+		   batadv_print_vid(vid));
+	batadv_dbg(BATADV_DBG_DAT, bat_priv,
+		   "Snooped from DHCPACK (client-side): %pI4, %pM (vid: %i)\n",
+		   yiaddr, chaddr, batadv_print_vid(vid));
+}
+
+/**
  * batadv_dat_drop_broadcast_packet() - check if an ARP request has to be
  *  dropped (because the node has already obtained the reply via DAT) or not
  * @bat_priv: the bat priv with all the soft interface information
diff --git a/net/batman-adv/distributed-arp-table.h b/net/batman-adv/distributed-arp-table.h
index a0459602..cf58d230 100644
--- a/net/batman-adv/distributed-arp-table.h
+++ b/net/batman-adv/distributed-arp-table.h
@@ -46,6 +46,10 @@  void batadv_dat_snoop_outgoing_arp_reply(struct batadv_priv *bat_priv,
 					 struct sk_buff *skb);
 bool batadv_dat_snoop_incoming_arp_reply(struct batadv_priv *bat_priv,
 					 struct sk_buff *skb, int hdr_size);
+void batadv_dat_snoop_outgoing_dhcp_ack(struct batadv_priv *bat_priv,
+					struct sk_buff *skb,
+					__be16 proto,
+					unsigned short vid);
 bool batadv_dat_drop_broadcast_packet(struct batadv_priv *bat_priv,
 				      struct batadv_forw_packet *forw_packet);
 
@@ -140,6 +144,13 @@  batadv_dat_snoop_incoming_arp_reply(struct batadv_priv *bat_priv,
 	return false;
 }
 
+static inline void
+batadv_dat_snoop_outgoing_dhcp_ack(struct batadv_priv *bat_priv,
+				   struct sk_buff *skb, __be16 proto,
+				   unsigned short vid)
+{
+}
+
 static inline bool
 batadv_dat_drop_broadcast_packet(struct batadv_priv *bat_priv,
 				 struct batadv_forw_packet *forw_packet)
diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index 1485263a..a8559629 100644
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -212,6 +212,7 @@  static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
 	enum batadv_forw_mode forw_mode;
 	struct batadv_orig_node *mcast_single_orig = NULL;
 	int network_offset = ETH_HLEN;
+	__be16 proto;
 
 	if (atomic_read(&bat_priv->mesh_state) != BATADV_MESH_ACTIVE)
 		goto dropped;
@@ -223,12 +224,15 @@  static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
 	vid = batadv_get_vid(skb, 0);
 	ethhdr = eth_hdr(skb);
 
-	switch (ntohs(ethhdr->h_proto)) {
+	proto = ethhdr->h_proto;
+
+	switch (ntohs(proto)) {
 	case ETH_P_8021Q:
 		vhdr = vlan_eth_hdr(skb);
+		proto = vhdr->h_vlan_encapsulated_proto;
 
 		/* drop batman-in-batman packets to prevent loops */
-		if (vhdr->h_vlan_encapsulated_proto != htons(ETH_P_BATMAN)) {
+		if (proto != htons(ETH_P_BATMAN)) {
 			network_offset += VLAN_HLEN;
 			break;
 		}
@@ -256,6 +260,9 @@  static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
 			goto dropped;
 	}
 
+	/* Snoop address candidates from DHCPACKs for early DAT filling */
+	batadv_dat_snoop_outgoing_dhcp_ack(bat_priv, skb, proto, vid);
+
 	/* don't accept stp packets. STP does not help in meshes.
 	 * better use the bridge loop avoidance ...
 	 *