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