The current Linux kernel currently contains the generate_random_uuid()
function, which creates - based on RFC 4122 - truly random UUIDs and
provides them to userspace through /proc/sys/kernel/random/boot_id
and /proc/sys/kernel/random/uuid.
The attached patch additionally adds the "Time-based UUID" variant
of RFC 4122 to the Linux Kernel.
With this patch applied, userspace applications may easily get real unique
time-based UUIDs through /proc/sys/kernel/random/uuid_time.
The attached implementation uses getnstimeofday() to get more fine-grained
granularity than what would be possible with gettimeofday() in userspace.
As such it's in principle possible to provide a lot more UUIDs (if needed) per
time than in userspace.
Additionally a mutex takes care of the proper locking against a mistaken
double creation of UUIDs for simultanious running processes.
Signed-off-by: Helge Deller <[email protected]>
CC: [email protected]
drivers/char/random.c | 160 +++++++++++++++++++++++++++++++++++++++++++------
include/linux/sysctl.h | 5 -
2 files changed, 145 insertions(+), 20 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 1756b1f..3d6b6e0 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -239,6 +239,7 @@
#include <linux/spinlock.h>
#include <linux/percpu.h>
#include <linux/cryptohash.h>
+#include <linux/if_arp.h>
#include <asm/processor.h>
#include <asm/uaccess.h>
@@ -1174,12 +1177,134 @@ EXPORT_SYMBOL(generate_random_uuid);
static int min_read_thresh = 8, min_write_thresh;
static int max_read_thresh = INPUT_POOL_WORDS * 32;
static int max_write_thresh = INPUT_POOL_WORDS * 32;
-static char sysctl_bootid[16];
+static unsigned char sysctl_bootid[16] __read_mostly;
/*
- * These functions is used to return both the bootid UUID, and random
- * UUID. The difference is in whether table->data is NULL; if it is,
- * then a new UUID is generated and returned to the user.
+ * Generate time based UUID (RFC 4122)
+ *
+ * This function is protected with a mutex to ensure system-wide
+ * uniqiness of the new time based UUID.
+ */
+static void generate_random_uuid_time(unsigned char uuid_out[16])
+{
+ static DEFINE_MUTEX(uuid_mutex);
+ static u64 last_time_all;
+ static u16 clock_seq, clock_seq_started;
+ static unsigned char last_mac[ETH_ALEN];
+ static int clock_seq_initialized __read_mostly;
+
+ struct timespec ts;
+ u64 time_all;
+ struct net_device *d;
+ int netdev_found = 0;
+
+ mutex_lock(&uuid_mutex);
+
+ /* Determine 60-bit timestamp value. For UUID version 1, this is
+ * represented by Coordinated Universal Time (UTC) as a count of 100-
+ * nanosecond intervals since 00:00:00.00, 15 October 1582 (the date of
+ * Gregorian reform to the Christian calendar).
+ */
+try_again:
+ getnstimeofday(&ts);
+ time_all = ((u64) ts.tv_sec) * (NSEC_PER_SEC/100);
+ time_all += ts.tv_nsec / 100;
+
+ /* add offset from Gregorian Calendar to Jan 1 1970 */
+ time_all += 12219292800000ULL * (NSEC_PER_MSEC/100);
+ time_all &= 0x0fffffffffffffffULL; /* limit to 60 bits */
+ uuid_out[3] = (u8) time_all;
+ uuid_out[2] = (u8) (time_all >> 8);
+ uuid_out[1] = (u8) (time_all >> 16);
+ uuid_out[0] = (u8) (time_all >> 24);
+ uuid_out[5] = (u8) (time_all >> 32);
+ uuid_out[4] = (u8) (time_all >> 40);
+ uuid_out[7] = (u8) (time_all >> 48);
+ uuid_out[6] = (u8) (time_all >> 56);
+
+ /* Determine clock sequence (max. 14 bit) */
+ if (unlikely(!clock_seq_initialized)) {
+ get_random_bytes(&clock_seq, sizeof(clock_seq));
+ clock_seq &= 0x3fff;
+ clock_seq_started = clock_seq;
+ clock_seq_initialized = 1;
+ } else {
+ if (unlikely(time_all <= last_time_all)) {
+inc_clock_seq: clock_seq = (clock_seq+1) & 0x3fff;
+ if (unlikely(clock_seq == clock_seq_started)) {
+ clock_seq = (clock_seq-1) & 0x3fff;
+ goto try_again; /* wait until time advanced */
+ }
+ } else
+ clock_seq_started = clock_seq;
+ }
+ last_time_all = time_all;
+
+ uuid_out[8] = clock_seq >> 8;
+ uuid_out[9] = clock_seq & 0xff;
+
+ /* Set the spatially unique node identifier */
+#ifdef CONFIG_NET
+ read_lock(&dev_base_lock);
+ for_each_netdev(&init_net, d) {
+ if (d->type == ARPHRD_ETHER && d->addr_len == ETH_ALEN
+ && d != init_net.loopback_dev) {
+ memcpy(&uuid_out[10], d->dev_addr, ETH_ALEN);
+ netdev_found = 1;
+ break;
+ }
+ }
+ read_unlock(&dev_base_lock);
+#endif
+ if (unlikely(!netdev_found)) {
+ /* use bootid's nodeID if no network interface found */
+ if (sysctl_bootid[8] == 0)
+ generate_random_uuid(sysctl_bootid);
+ memcpy(&uuid_out[10], &sysctl_bootid[10], ETH_ALEN);
+ }
+ /* if MAC/NodeID changed, create a new clock_seq value */
+ if (unlikely(memcmp(&uuid_out[10], &last_mac, ETH_ALEN))) {
+ memcpy(&last_mac, &uuid_out[10], ETH_ALEN);
+ /* for very first UUID, do not increment clock_seq */
+ if (unlikely(clock_seq_initialized == 1))
+ clock_seq_initialized = 2;
+ else
+ goto inc_clock_seq;
+ }
+
+ /* Set UUID version to 1 --- time-based generation */
+ uuid_out[6] = (uuid_out[6] & 0x0F) | 0x10;
+ /* Set the UUID variant to DCE */
+ uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
+
+ mutex_unlock(&uuid_mutex);
+}
+
+
+/*
+ * Get UUID based on requested type.
+ */
+static unsigned char *get_uuid(void *extra1, unsigned char *uuid)
+{
+ switch ((int) extra1) {
+ case RANDOM_BOOT_ID:
+ uuid = sysctl_bootid;
+ if (unlikely(uuid[8] == 0))
+ generate_random_uuid(uuid);
+ break;
+ case RANDOM_UUID:
+ generate_random_uuid(uuid);
+ break;
+ case RANDOM_UUID_TIME:
+ generate_random_uuid_time(uuid);
+ break;
+ }
+ return uuid;
+}
+
+/*
+ * These functions are used to return the bootid UUID, random UUID and
+ * time based UUID.
*
* If the user accesses this via the proc interface, it will be returned
* as an ASCII string in the standard UUID format. If accesses via the
@@ -1191,13 +1316,13 @@ static int proc_do_uuid(ctl_table *table, int write, struct file *filp,
ctl_table fake_table;
unsigned char buf[64], tmp_uuid[16], *uuid;
- uuid = table->data;
- if (!uuid) {
- uuid = tmp_uuid;
- uuid[8] = 0;
+ /* random/time UUIDs need to be read completely at once */
+ if ((int)table->extra1 != RANDOM_BOOT_ID && *ppos > 0) {
+ *lenp = 0;
+ return 0;
}
- if (uuid[8] == 0)
- generate_random_uuid(uuid);
+
+ uuid = get_uuid(table->extra1, tmp_uuid);
sprintf(buf, "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-"
"%02x%02x%02x%02x%02x%02x",
@@ -1221,13 +1346,7 @@ static int uuid_strategy(ctl_table *table, int __user *name, int nlen,
if (!oldval || !oldlenp)
return 1;
- uuid = table->data;
- if (!uuid) {
- uuid = tmp_uuid;
- uuid[8] = 0;
- }
- if (uuid[8] == 0)
- generate_random_uuid(uuid);
+ uuid = get_uuid(table->extra1, tmp_uuid);
if (get_user(len, oldlenp))
return -EFAULT;
@@ -1284,11 +1403,11 @@ ctl_table random_table[] = {
{
.ctl_name = RANDOM_BOOT_ID,
.procname = "boot_id",
- .data = &sysctl_bootid,
.maxlen = 16,
.mode = 0444,
.proc_handler = &proc_do_uuid,
.strategy = &uuid_strategy,
+ .extra1 = (void *) RANDOM_BOOT_ID,
},
{
.ctl_name = RANDOM_UUID,
@@ -1297,6 +1416,13 @@ ctl_table random_table[] = {
.mode = 0444,
.proc_handler = &proc_do_uuid,
.strategy = &uuid_strategy,
+ .extra1 = (void *) RANDOM_UUID,
+ },
+ {
+ .procname = "uuid_time",
+ .mode = 0444,
+ .proc_handler = &proc_do_uuid,
+ .extra1 = (void *) RANDOM_UUID_TIME,
},
{ .ctl_name = 0 }
};
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index e99171f..dd09d97 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -248,8 +248,9 @@ enum
RANDOM_ENTROPY_COUNT=2,
RANDOM_READ_THRESH=3,
RANDOM_WRITE_THRESH=4,
- RANDOM_BOOT_ID=5,
- RANDOM_UUID=6
+ RANDOM_BOOT_ID=5, /* rfc4122 version 4, boot UUID */
+ RANDOM_UUID=6, /* rfc4122 version 4, random-based */
+ RANDOM_UUID_TIME=7 /* rfc4122 version 1, time-based */
};
/* /proc/sys/kernel/pty */
-
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