Re: [B.A.T.M.A.N.] [RFC 4/6] batman-adv: Adds necessary functions for NDP, like checking if a packet is valid or creating a Neighbor Advertisement

On Mon, Jul 08, 2013 at 03:12:43AM +0300, mihail.costea2005@gmail.com wrote:

From: Mihail Costea mihail.costea90@gmail.com

Adds functions needed for NDP snooping, like getting the IPv6 addresses or getting the target HW address from an Neighbor Advertisement (NA).

typo: an -> a

Also added functions to create NA for Neighbor Solicitations

use always the same form: added -> adds

that have already the HW address in DAT.

Signed-off-by: Mihail Costea mihail.costea90@gmail.com Signed-off-by: Stefan Popa Stefan.A.Popa@intel.com Reviewed-by: Stefan Popa Stefan.A.Popa@intel.com

---

distributed-arp-table.c | 319 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 319 insertions(+)

diff --git a/distributed-arp-table.c b/distributed-arp-table.c index f941913..d0b9e95 100644 --- a/distributed-arp-table.c +++ b/distributed-arp-table.c @@ -20,7 +20,9 @@ #include <linux/if_ether.h> #include <linux/if_arp.h> #include <linux/if_vlan.h> +#include <net/addrconf.h> #include <net/arp.h> +#include <net/ipv6.h>

#include "main.h" #include "hash.h" @@ -981,6 +983,323 @@ static unsigned short batadv_dat_get_vid(struct sk_buff *skb, int *hdr_size) return vid; }

+#if IS_ENABLED(CONFIG_IPV6) +/**

• • batadv_ndisc_hw_src - get source hw address from a packet
• • @skb: packet to check
• • @hdr_size: size of the encapsulation header
• • Returns source hw address of the skb packet.
• */

+static uint8_t *batadv_ndisc_hw_src(struct sk_buff *skb, int hdr_size) +{

• struct ethhdr *ethhdr;

please put a blank line after variable declarations.

• ethhdr = (struct ethhdr *)(skb->data + hdr_size);
• return (uint8_t *)ethhdr->h_source;

+}

+/**

• • batadv_ndisc_hw_dst - get destination hw address from a packet
• • @skb: packet to check
• • @hdr_size: size of the encapsulation header
• • Returns destination hw address of the skb packet.
• */

+static uint8_t *batadv_ndisc_hw_dst(struct sk_buff *skb, int hdr_size) +{

• struct ethhdr *ethhdr;

same here

• ethhdr = (struct ethhdr *)(skb->data + hdr_size);
• return (uint8_t *)ethhdr->h_dest;

+}

+/**

• • batadv_ndisc_ipv6_src - get source IPv6 address from a packet
• • @skb: packet to check
• • @hdr_size: size of the encapsulation header
• • Returns source IPv6 address of the skb packet.
• */

+static struct in6_addr *batadv_ndisc_ipv6_src(struct sk_buff *skb,

• 			      int hdr_size)
  

+{

• struct ipv6hdr *ipv6hdr;

same here

• ipv6hdr = (struct ipv6hdr *)(skb->data + hdr_size + ETH_HLEN);
• return &ipv6hdr->saddr;

+}

+/**

• • batadv_ndisc_ipv6_dst - get destination IPv6 address from a packet
• • @skb: packet to check
• • @hdr_size: size of the encapsulation header
• • Returns destination IPv6 address of the skb packet.
• */

+static struct in6_addr *batadv_ndisc_ipv6_dst(struct sk_buff *skb,

• 			      int hdr_size)
  

+{

• struct ipv6hdr *ipv6hdr;

same here

• ipv6hdr = (struct ipv6hdr *)(skb->data + hdr_size + ETH_HLEN);
• return &ipv6hdr->daddr;

+}

+/**

• • batadv_ndisc_ipv6_target - get target IPv6 address from a NS/NA packet
• • @skb: packet to check
• • @hdr_size: size of the encapsulation header
• • Returns target IPv6 address of the skb packet.
• */

+static struct in6_addr *batadv_ndisc_ipv6_target(struct sk_buff *skb,

• 				 int hdr_size)
  

+{

• return (struct in6_addr *)(skb->data + hdr_size + ETH_HLEN +

• 	sizeof(struct ipv6hdr) + sizeof(struct icmp6hdr));
  

please, use the needed local variables to make this statement more readable and and to align it in a proper way.

+}

+/**

• • batadv_ndisc_hw_opt - get hw address from NS/NA packet options
• • @skb: packet to check
• • @hdr_size: size of the encapsulation header
• • @type: type of the address (ND_OPT_SOURCE_LL_ADDR or ND_OPT_TARGET_LL_ADDR)
• • The address can be either the source link-layer address
• • or the target link-layer address.
• • For more info see RFC2461.
• • Returns hw address from packet options.
• */

+static uint8_t *batadv_ndisc_hw_opt(struct sk_buff *skb, int hdr_size,

• 		    uint8_t type)
  

+{

• unsigned char *opt_addr;
• opt_addr = skb->data + hdr_size + ETH_HLEN +

• 	sizeof(struct ipv6hdr) + sizeof(struct icmp6hdr) +
  

• 	sizeof(struct in6_addr);
  

align this statement properly. it should be:

like_this = this + that + and_whatever + we_need;

• /* test if option header is ok */

Please, be a bit more verbose in this comment. What are we checking here? why != 1? What does that mean? Otherwise it will be difficult for other people out of these patches business to understand

• if (*opt_addr != type || *(opt_addr + 1) != 1)

• return NULL;
  

• return (uint8_t *)(opt_addr + 2);

and why skipping the initial two bytes? Maybe you should describe what opt_addr contains? this will probably help to better understand what this statement is doing.

+}

+/**

• • batadv_ndisc_get_type - get icmp6 packet type

I think you can directly call this function "batadv_icmpv6_get_type". It may be re-used in the future for the same purpose but somewhere else :)

• • @bat_priv: the bat priv with all the soft interface information
• • @skb: packet to check
• • @hdr_size: size of the encapsulation header
• • Returns the icmp6 type, or 0 if packet is not a valid icmp6 packet.
• */

+static __u8 batadv_ndisc_get_type(struct batadv_priv *bat_priv,

in the batman-adv code we use stdint: __u8 -> uint8_t (there are other spots where you use __8)

• 		  struct sk_buff *skb, int hdr_size)
  

+{

• struct ethhdr *ethhdr;
• struct ipv6hdr *ipv6hdr;
• struct icmp6hdr *icmp6hdr;
• __u8 type = 0;
• /* pull headers */
• if (unlikely(!pskb_may_pull(skb, hdr_size + ETH_HLEN +

• 	sizeof(struct ipv6hdr) + sizeof(struct icmp6hdr))))
  

please properly align this statement too. I think checkpatch would have complained about this. You can use tabs + spaces to correctly align.

• goto out;
  

• /* get the ethernet header */

remove this comment :) Variables are named properly and this is obvious.

• ethhdr = (struct ethhdr *)(skb->data + hdr_size);
• if (ethhdr->h_proto != htons(ETH_P_IPV6))

• goto out;
  

• /* get the ipv6 header */

same

• ipv6hdr = (struct ipv6hdr *)(skb->data + hdr_size + ETH_HLEN);
• if (ipv6hdr->nexthdr != IPPROTO_ICMPV6)

• goto out;
  

• /* get the icmpv6 header */
• icmp6hdr = (struct icmp6hdr *)(skb->data + hdr_size + ETH_HLEN +

• 	sizeof(struct ipv6hdr));
  

alignment..should line up to the opening parenthesis.

(blablabla *)(like this);

• /* check whether the ndisc packet carries a valid icmp6 header */
• if (ipv6hdr->hop_limit != 255)

• goto out;
  

• if (icmp6hdr->icmp6_code != 0)

• goto out;
  

• type = icmp6hdr->icmp6_type;

+out:

• return type;

+}

+/**

• • batadv_ndisc_is_valid - check if a ndisc packet is valid
• • @bat_priv: the bat priv with all the soft interface information
• • @skb: packet to check
• • @hdr_size: size of the encapsulation header
• • @ndisc_type: type of ndisc packet to check
• • Check if all IPs are valid (source, destination, target) and if
• • options hw address is valid too.
• • Some options might be ignored, like NS packets sent automatically
• • for verification of the reachability of a neighbor.
• • Returns true if packet is valid, otherwise false if invalid or ignored.
• */

+static bool batadv_ndisc_is_valid(struct batadv_priv *bat_priv,

• 		  struct sk_buff *skb, int hdr_size,
  

• 		  int ndisc_type)
  

+{

• uint8_t *hw_target = NULL;
• struct in6_addr *ipv6_src, *ipv6_dst, *ipv6_target;
• __u8 type = batadv_ndisc_get_type(bat_priv, skb, hdr_size);
• int ndisc_hdr_len = hdr_size + ETH_HLEN + sizeof(struct ipv6hdr) +

• 	    sizeof(struct icmp6hdr) + sizeof(struct in6_addr) +
  

• 	    8; /* ndisc options length */
  

when the assignment is too long, please do it after the declarations. Improves readability.

• if (type != ndisc_type)

• return false;
  

• if (unlikely(!pskb_may_pull(skb, ndisc_hdr_len)))

• return false;
  

• /* Check for bad NA/NS. If the ndisc message is not sane, DAT

• * will simply ignore it
  

• */
  

• if (type == NDISC_NEIGHBOUR_SOLICITATION)

• hw_target = batadv_ndisc_hw_opt(skb, hdr_size,
  

• 				ND_OPT_SOURCE_LL_ADDR);
  

• else if (type == NDISC_NEIGHBOUR_ADVERTISEMENT)

• hw_target = batadv_ndisc_hw_opt(skb, hdr_size,
  

• 				ND_OPT_TARGET_LL_ADDR);
  

• if (!hw_target || is_zero_ether_addr(hw_target) ||

•    is_multicast_ether_addr(hw_target))
  

• return false;
  

• ipv6_src = batadv_ndisc_ipv6_src(skb, hdr_size);
• ipv6_dst = batadv_ndisc_ipv6_dst(skb, hdr_size);
• ipv6_target = batadv_ndisc_ipv6_target(skb, hdr_size);
• if (ipv6_addr_loopback(ipv6_src) || ipv6_addr_loopback(ipv6_dst) ||

•    ipv6_addr_is_multicast(ipv6_src) ||
  

•    ipv6_addr_is_multicast(ipv6_target))
  

• return false;
  

• /* ignore messages with unspecified address */
• if (ipv6_addr_any(ipv6_src) || ipv6_addr_any(ipv6_dst) ||

•    ipv6_addr_any(ipv6_target))
  

• return false;
  

• /* ignore the verification of the reachability of a neighbor */
• if (type == NDISC_NEIGHBOUR_SOLICITATION &&

•    !ipv6_addr_is_multicast(ipv6_dst))
  

• return false;
  

• return true;

+}

+static void batadv_ndisc_ip6_hdr(struct sock *sk, struct sk_buff *skb,

• 		 struct net_device *dev,
  

• 		 const struct in6_addr *ipv6_src,
  

• 		 const struct in6_addr *ipv6_dst,
  

• 		 int proto, int len)
  

alignment?

+{

• struct ipv6_pinfo *np = inet6_sk(sk);
• struct ipv6hdr *hdr;
• skb->protocol = htons(ETH_P_IPV6);
• skb->dev = dev;
• skb_reset_network_header(skb);
• skb_put(skb, sizeof(struct ipv6hdr));
• hdr = ipv6_hdr(skb);
• *(__be32 *)hdr = htonl(0x60000000);

What does this constant mean? you are writing on the IPv6 header? why not writing in one of its fields (I guess you wanted to write in the first one)?

• hdr->payload_len = htons(len);

I think len can be declared int16_t to avoid using wrong values? (here and where you call this function)

• hdr->nexthdr = proto;
• hdr->hop_limit = np->hop_limit;
• hdr->saddr = *ipv6_src;
• hdr->daddr = *ipv6_dst;

+}

+/**

• • batadv_ndisc_create_na - create an NA for a solicited NS
• • @net_device: the devices for which the packet is created
• • @ipv6_dst: destination IPv6
• • @ipv6_target: target IPv6 (same with source IPv6)
• • @hw_dst: destination HW Address
• • @hw_target: target HW Address (same with source HW Address)
• • @router: 1 if target is a router, else 0
• • @solicited: 1 if this is a solicited NA, else 0
• • @override: 1 if the target entry should be override, else 0
• • For more info see RFC2461.

If you want to cite the RFC think you should provide also a section? The "Neighbor Discovery for IP Version 6" RFC is a bit too much is I only want to understand what a NA or NS is and how the NA is created.

By the way, ok for reading the RFC, but I think you can write a bit more about what the function is doing: e.g. create a new skb containing an NA which fields are initialised with the value passed as argument. Seems obvious, but better safe than sorry :) Kernel Doc is shown without the code if you compile it.

• • Returns the newly created skb, otherwise NULL.
• */

+static struct +sk_buff *batadv_ndisc_create_na(struct net_device *dev,

• 		const struct in6_addr *ipv6_dst,
  

• 		const struct in6_addr *ipv6_target,
  

• 		const uint8_t *hw_dst,
  

• 		const uint8_t *hw_target,
  

• 		int router, int solicited, int override)
  

if these variables can only be 0 or 1, why not using bool?

+{

• struct net *net = dev_net(dev);
• struct sock *sk = net->ipv6.ndisc_sk;
• struct sk_buff *skb;
• struct icmp6hdr *icmp6hdr;
• int hlen = LL_RESERVED_SPACE(dev);
• int tlen = dev->needed_tailroom;
• int len, err;
• u8 *opt;

uint8_t

• /* alloc space for skb */
• len = sizeof(struct icmp6hdr) + sizeof(*ipv6_target) + 8;

write in the comment what is this 8. Otherwise, since you use it more than once, create a define with a descriptive name and it instead of the 8.

• skb = sock_alloc_send_skb(sk,

• 		  (MAX_HEADER + sizeof(struct ipv6hdr) +
  

why these parenthesis here?

• 		   len + hlen + tlen),
  

I guess hlen is ETH_HLEN? what does LL_RESERVED_SPACE exactly return? and why using needed_tailroom? what does it comport in this case? We never used that during SKB allocation...this is why I am asking.

• 		  1, &err);
  

and why are you using this function to allocate the skb? In the rest of the code we always use netdev_alloc_skb_ip_align() (that also takes care of properly aligning the skb).

• if (!skb)

• return NULL;
  

• skb_reserve(skb, hlen);
• batadv_ndisc_ip6_hdr(sk, skb, dev, ipv6_target, ipv6_dst,

• 	     IPPROTO_ICMPV6, len);
  

• skb->transport_header = skb->tail;

why you care about setting the transport header? You could also use skb_set_transport_header() passing a proper offset rather than directly using skb->tail. Following the skb logic is "sometimes" not straightforward, therefore it is better to use the provided functions when possible.

• skb_put(skb, len);
• /* fill the device header for the NA frame */
• if (dev_hard_header(skb, dev, ETH_P_IPV6, hw_dst,

• 	    hw_target, skb->len) < 0) {
  

• kfree_skb(skb);
  

• return NULL;
  

• }

mh..we never used this function as we assume that the interface below batman-adv is carrying 802.3 frame only. But looks interesting :)

• /* set icmpv6 header */
• icmp6hdr = (struct icmp6hdr *)skb_transport_header(skb);

ah now I understood why you have set the transport_header :)

• icmp6hdr->icmp6_type = NDISC_NEIGHBOUR_ADVERTISEMENT;
• icmp6hdr->icmp6_router = router;
• icmp6hdr->icmp6_solicited = solicited;
• icmp6hdr->icmp6_override = override;
• /* set NA target and options */
• opt = skb_transport_header(skb) + sizeof(*icmp6hdr);
• *(struct in6_addr *)opt = *ipv6_target;
• opt += sizeof(*ipv6_target);
• opt[0] = ND_OPT_TARGET_LL_ADDR;
• opt[1] = 1;
• memcpy(opt + 2, hw_target, dev->addr_len);

ah, these are the famous 8 bytes :) So hard to discover! :D

• icmp6hdr->icmp6_cksum = csum_ipv6_magic(ipv6_target, ipv6_dst, len,

• 				IPPROTO_ICMPV6,
  

• 				csum_partial(icmp6hdr, len, 0));
  

• return skb;

+} +#endif

/**

• batadv_dat_snoop_outgoing_pkt_request - snoop the ARP request and try to
• answer using DAT

-- 1.7.10.4