net/ipv6/output_core.c

   1 #include <linux/export.h>
   2 #include <linux/skbuff.h>
   3 #include <net/ip.h>
   4 #include <net/ipv6.h>
   5
   6 /* This function exists only for tap drivers that must support broken
   7  * clients requesting UFO without specifying an IPv6 fragment ID.
   8  *
   9  * This is similar to ipv6_select_ident() but we use an independent hash
  10  * seed to limit information leakage.
  11  */
  12 void ipv6_proxy_select_ident(struct sk_buff *skb)
  13 {
  14         static u32 ip6_proxy_idents_hashrnd __read_mostly;
  15         static bool hashrnd_initialized = false;
  16         struct in6_addr buf[2];
  17         struct in6_addr *addrs;
  18         u32 hash, id;
  19
  20         addrs = skb_header_pointer(skb,
  21                                    skb_network_offset(skb) +
  22                                    offsetof(struct ipv6hdr, saddr),
  23                                    sizeof(buf), buf);
  24         if (!addrs)
  25                 return;
  26
  27         if (unlikely(!hashrnd_initialized)) {
  28                 hashrnd_initialized = true;
  29                 get_random_bytes(&ip6_proxy_idents_hashrnd,
  30                                  sizeof(ip6_proxy_idents_hashrnd));
  31         }
  32         hash = __ipv6_addr_jhash(&addrs[1], ip6_proxy_idents_hashrnd);
  33         hash = __ipv6_addr_jhash(&addrs[0], hash);
  34
  35         id = ip_idents_reserve(hash, 1);
  36         skb_shinfo(skb)->ip6_frag_id = htonl(id);
  37 }
  38 EXPORT_SYMBOL_GPL(ipv6_proxy_select_ident);