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- ===============================================================================
- This patch makes MAC addresses of network interfaces predictable. In
- particular, it adds a small routine that computes MAC addresses of based on
- a SHA1 hash of the virtual machine name and interface ID.
- TECHNICAL INFORMATION:
- Applies to vanilla kernel 3.9.4.
- ===============================================================================
- --- a/arch/um/Kconfig.net
- +++ b/arch/um/Kconfig.net
- @@ -21,6 +21,19 @@ config UML_NET
- enable at least one of the following transport options to actually
- make use of UML networking.
-
- +config UML_NET_RANDOM_MAC
- + bool "Use random MAC addresses for network interfaces"
- + default n
- + depends on UML_NET
- + help
- + Virtual network devices inside a User-Mode Linux instance must be
- + assigned a MAC (Ethernet) address. If none is specified on the UML
- + command line, one must be automatically computed. If this option is
- + enabled, a randomly generated address is used. Otherwise, if this
- + option is disabled, the address is generated from a SHA1 hash of
- + the umid of the UML instance and the interface name. The latter choice
- + is useful to make MAC addresses predictable.
- +
- config UML_NET_ETHERTAP
- bool "Ethertap transport"
- depends on UML_NET
- --- a/arch/um/drivers/net_kern.c
- +++ b/arch/um/drivers/net_kern.c
- @@ -25,6 +25,13 @@
- #include <net_kern.h>
- #include <net_user.h>
-
- +#include <crypto/sha.h>
- +#include <linux/string.h>
- +#include <linux/crypto.h>
- +#include <linux/err.h>
- +#include <linux/scatterlist.h>
- +#include "os.h"
- +
- #define DRIVER_NAME "uml-netdev"
-
- static DEFINE_SPINLOCK(opened_lock);
- @@ -295,11 +302,47 @@ static void uml_net_user_timer_expire(un
- #endif
- }
-
- +#ifndef CONFIG_UML_NET_RANDOM_MAC
- +
- +/* Compute a SHA1 hash of the UML instance's id and
- + * * an interface name. */
- +static int compute_hash(const char *umid, const char *ifname, char *hash) {
- + char vmif[1024];
- + struct scatterlist sg;
- + struct crypto_hash *tfm;
- + struct hash_desc desc;
- +
- + strcpy (vmif, umid);
- + strcat (vmif, ifname);
- +
- + tfm = crypto_alloc_hash("sha1", 0, CRYPTO_ALG_ASYNC);
- + if (IS_ERR(tfm))
- + return 1;
- +
- + desc.tfm = tfm;
- + desc.flags = 0;
- +
- + sg_init_table(&sg, 1);
- + sg_set_buf(&sg, vmif, strlen(vmif));
- +
- + if (crypto_hash_digest(&desc, &sg, strlen(vmif), hash)) {
- + crypto_free_hash(tfm);
- + return 1;
- + }
- +
- + crypto_free_hash(tfm);
- +
- + return 0;
- +}
- +
- +#endif
- +
- static void setup_etheraddr(struct net_device *dev, char *str)
- {
- unsigned char *addr = dev->dev_addr;
- char *end;
- int i;
- + u8 hash[SHA1_DIGEST_SIZE];
-
- if (str == NULL)
- goto random;
- @@ -340,9 +383,26 @@ static void setup_etheraddr(struct net_d
- return;
-
- random:
- +#ifdef CONFIG_UML_NET_RANDOM_MAC
- printk(KERN_INFO
- "Choosing a random ethernet address for device %s\n", dev->name);
- eth_hw_addr_random(dev);
- +#else
- + printk(KERN_INFO
- + "Computing a digest to use as ethernet address for device %s\n", dev->name);
- + if (compute_hash(get_umid(), dev->name, hash)) {
- + printk(KERN_WARNING
- + "Could not compute digest to use as ethernet address for device %s. "
- + "Using random address instead.\n", dev->name);
- + random_ether_addr(addr);
- + }
- + else {
- + for (i=0; i < 6; i++)
- + addr[i] = (hash[i] + hash[i+6]) % 0x100;
- + }
- + addr [0] &= 0xfe; /* clear multicast bit */
- + addr [0] |= 0x02; /* set local assignment bit (IEEE802) */
- +#endif
- }
-
- static DEFINE_SPINLOCK(devices_lock);
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