target/linux/uml/patches-4.1/102-pseudo-random-mac.patch

   1 ===============================================================================
   2
   3 This patch makes MAC addresses of network interfaces predictable. In
   4 particular, it adds a small routine that computes MAC addresses of based on
   5 a SHA1 hash of the virtual machine name and interface ID.
   6
   7 TECHNICAL INFORMATION:
   8
   9 Applies to vanilla kernel 3.9.4.
  10
  11 ===============================================================================
  12 --- a/arch/um/Kconfig.net
  13 +++ b/arch/um/Kconfig.net
  14 @@ -21,6 +21,19 @@ config UML_NET
  15          enable at least one of the following transport options to actually
  16          make use of UML networking.
  17
  18 +config UML_NET_RANDOM_MAC
  19 +       bool "Use random MAC addresses for network interfaces"
  20 +       default n
  21 +       depends on UML_NET
  22 +       help
  23 +        Virtual network devices inside a User-Mode Linux instance must be
  24 +        assigned a MAC (Ethernet) address. If none is specified on the UML
  25 +        command line, one must be automatically computed. If this option is
  26 +        enabled, a randomly generated address is used. Otherwise, if this
  27 +        option is disabled, the address is generated from a SHA1 hash of
  28 +        the umid of the UML instance and the interface name. The latter choice
  29 +        is useful to make MAC addresses predictable.
  30 +
  31  config UML_NET_ETHERTAP
  32         bool "Ethertap transport"
  33         depends on UML_NET
  34 --- a/arch/um/drivers/net_kern.c
  35 +++ b/arch/um/drivers/net_kern.c
  36 @@ -25,6 +25,13 @@
  37  #include <net_kern.h>
  38  #include <net_user.h>
  39
  40 +#include <crypto/sha.h>
  41 +#include <linux/string.h>
  42 +#include <linux/crypto.h>
  43 +#include <linux/err.h>
  44 +#include <linux/scatterlist.h>
  45 +#include "os.h"
  46 +
  47  #define DRIVER_NAME "uml-netdev"
  48
  49  static DEFINE_SPINLOCK(opened_lock);
  50 @@ -295,11 +302,47 @@ static void uml_net_user_timer_expire(un
  51  #endif
  52  }
  53
  54 +#ifndef CONFIG_UML_NET_RANDOM_MAC
  55 +
  56 +/* Compute a SHA1 hash of the UML instance's id and
  57 + *  * an interface name. */
  58 +static int compute_hash(const char *umid, const char *ifname, char *hash) {
  59 +       char vmif[1024];
  60 +       struct scatterlist sg;
  61 +       struct crypto_hash *tfm;
  62 +       struct hash_desc desc;
  63 +
  64 +       strcpy (vmif, umid);
  65 +       strcat (vmif, ifname);
  66 +
  67 +       tfm = crypto_alloc_hash("sha1", 0, CRYPTO_ALG_ASYNC);
  68 +       if (IS_ERR(tfm))
  69 +               return 1;
  70 +
  71 +       desc.tfm = tfm;
  72 +       desc.flags = 0;
  73 +
  74 +       sg_init_table(&sg, 1);
  75 +       sg_set_buf(&sg, vmif, strlen(vmif));
  76 +
  77 +       if (crypto_hash_digest(&desc, &sg, strlen(vmif), hash)) {
  78 +               crypto_free_hash(tfm);
  79 +               return 1;
  80 +       }
  81 +
  82 +       crypto_free_hash(tfm);
  83 +
  84 +       return 0;
  85 +}
  86 +
  87 +#endif
  88 +
  89  static void setup_etheraddr(struct net_device *dev, char *str)
  90  {
  91         unsigned char *addr = dev->dev_addr;
  92         char *end;
  93         int i;
  94 +       u8 hash[SHA1_DIGEST_SIZE];
  95
  96         if (str == NULL)
  97                 goto random;
  98 @@ -340,9 +383,26 @@ static void setup_etheraddr(struct net_d
  99         return;
 100
 101  random:
 102 +#ifdef CONFIG_UML_NET_RANDOM_MAC
 103         printk(KERN_INFO
 104                "Choosing a random ethernet address for device %s\n", dev->name);
 105         eth_hw_addr_random(dev);
 106 +#else
 107 +       printk(KERN_INFO
 108 +              "Computing a digest to use as ethernet address for device %s\n", dev->name);
 109 +       if (compute_hash(get_umid(), dev->name, hash)) {
 110 +               printk(KERN_WARNING
 111 +                      "Could not compute digest to use as ethernet address for device %s. "
 112 +                      "Using random address instead.\n", dev->name);
 113 +               random_ether_addr(addr);
 114 +       }
 115 +       else {
 116 +               for (i=0; i < 6; i++)
 117 +                       addr[i] = (hash[i] + hash[i+6]) % 0x100;
 118 +       }
 119 +       addr [0] &= 0xfe; /* clear multicast bit */
 120 +       addr [0] |= 0x02; /* set local assignment bit (IEEE802) */
 121 +#endif
 122  }
 123
 124  static DEFINE_SPINLOCK(devices_lock);