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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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