From 46bb5945c60165249b8410a91be846c8cdb64270 Mon Sep 17 00:00:00 2001
From: Thomas Schmitt <scdbackup@gmx.net>
Date: Mon, 22 Oct 2012 18:59:07 +0200
Subject: [PATCH] Improved quality of random UUIDs

---
 libisofs/system_area.c | 49 ++++++++++++++++++++++++++----------------
 libisofs/system_area.h |  4 ----
 2 files changed, 31 insertions(+), 22 deletions(-)

diff --git a/libisofs/system_area.c b/libisofs/system_area.c
index 12644c2..abc5a9b 100644
--- a/libisofs/system_area.c
+++ b/libisofs/system_area.c
@@ -27,6 +27,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
+#include <fcntl.h>
 
 /* for gettimeofday() */
 #include <sys/time.h>
@@ -1852,12 +1853,13 @@ void iso_random_uuid(Ecma119Image *t, uint8_t uuid[16])
         0xee, 0x29, 0x9d, 0xfc, 0x65, 0xcc, 0x7c, 0x40,
         0x92, 0x61, 0x5b, 0xcd, 0x6f, 0xed, 0x08, 0x34
     };
+    static uint8_t uuid_urandom[16];
     uint32_t rnd, salt;
     struct timeval tv;
     struct timezone tz;
     pid_t pid;
-    static int counter = 0;
-    int i;
+    static int counter = 0, use_urandom = 0;
+    int i, ret, fd;
 #endif
 
 #ifdef Libisofs_with_uuid_generatE
@@ -1868,6 +1870,32 @@ void iso_random_uuid(Ecma119Image *t, uint8_t uuid[16])
 
 #else
 
+    /* First try /dev/urandom.
+       (Weakening the result by 8 bit saves a lot of pool entropy.)
+    */
+    if ((counter & 0xff) == 0) {
+        fd = open("/dev/urandom", O_RDONLY);
+        if (fd == -1)
+            goto fallback;
+        ret = read(fd, uuid_urandom, 16);
+        if (ret != 16) {
+            close(fd);
+            goto fallback;
+        }
+        /* Mark as UUID version 4 */
+        uuid_urandom[7] = (uuid_urandom[7] & 0x0f) | 0x40;
+        uuid_urandom[8] = (uuid_urandom[8] & 0x3f) | 0x80;
+        close(fd);
+        use_urandom = 1;
+    }
+    if (!use_urandom)
+        goto fallback;
+    memcpy(uuid, uuid_urandom, 16);
+    uuid[9] ^= counter & 0xff;
+    counter++;
+    return;
+
+fallback:;
     pid = getpid();
     salt = iso_crc32_gpt((unsigned char *) t, sizeof(Ecma119Image), 0) ^ pid; 
 
@@ -1883,7 +1911,7 @@ void iso_random_uuid(Ecma119Image *t, uint8_t uuid[16])
         u[i] = (salt >> (8 * i)) & 0xff;
     for (i = 0; i < 2; i++)
         u[4 + i] = (pid >> (8 * i)) & 0xff;
-    u[6] = ((salt >> 8) | (pid >> 16)) & 0xff;
+    u[6] = ((salt >> 8) ^ (pid >> 16)) & 0xff;
     rnd = ((0xffffff & tv.tv_sec) << 8) |
           (((tv.tv_usec >> 16) ^ (salt & 0xf0)) & 0xff);
     u[9] ^= counter & 0xff;
@@ -1900,21 +1928,6 @@ void iso_random_uuid(Ecma119Image *t, uint8_t uuid[16])
 }
 
 
-void iso_random_8byte(Ecma119Image *t, uint8_t result[8])
-{
-    uint8_t uuid[16];
-    int i;
-    
-    iso_random_uuid(t, uuid);
-    for (i = 0; i < 8; i++) {
-        if (i == 1) 
-            result[i] = uuid[9]; /* The intra-process counter */
-        else 
-            result[i] = uuid[i] ^ uuid[i + 8];
-    }
-}
-
-
 /* Probably already called by tail_writer_compute_data_blocks via
    iso_align_isohybrid
 */
diff --git a/libisofs/system_area.h b/libisofs/system_area.h
index 2be6da4..9585fde 100644
--- a/libisofs/system_area.h
+++ b/libisofs/system_area.h
@@ -186,10 +186,6 @@ unsigned int iso_crc32_gpt(unsigned char *data, int count, int flag);
 */
 void iso_random_uuid(Ecma119Image *t, uint8_t uuid[16]);
 
-/* Produces a weakly random variation of a hardcoded real random template
-*/
-void iso_random_8byte(Ecma119Image *t, uint8_t result[8]);
-
 
 /* The parameter struct for production of a single GPT entry.
    See also the partial GPT description in doc/boot_sectors.txt.