1 files changed, 55 insertions, 4 deletions

diff --git a/util-linux/mkswap.c b/util-linux/mkswap.c
index 167b9ee03..c4e30fd92 100644
--- a/util-linux/mkswap.c
+++ b/util-linux/mkswap.c
@@ -53,14 +53,65 @@ static void mkswap_selinux_setcontext(int fd, const char *path)
 #if ENABLE_DESKTOP
 static void mkswap_generate_uuid(uint8_t *buf)
 {
+        pid_t pid;
         unsigned i;
         char uuid_string[32];
 
-        /* rand() is guaranteed to generate at least [0, 2^15) range,
+        /* http://www.ietf.org/rfc/rfc4122.txt
+         *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+         * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+         * |                          time_low                             |
+         * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+         * |       time_mid                |         time_hi_and_version   |
+         * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+         * |clk_seq__and_variant           |         node (0-1)            |
+         * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+         * |                         node (2-5)                            |
+         * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+         * IOW, uuid has this layout:
+         * uint32_t time_low (big endian)
+         * uint16_t time_mid (big endian)
+         * uint16_t time_hi_and_version (big endian)
+         *  version is a 4-bit field:
+         *   1 Time-based version
+         *   2 DCE Security version, with embedded POSIX UIDs
+         *   3 Name-based version (MD5)
+         *   4 Randomly generated version
+         *   5 Name-based version (SHA-1)
+         * uint16_t clk_seq_and_variant (big endian)
+         *  variant is a 3-bit field:
+         *   0xx Reserved, NCS backward compatibility
+         *   10x The variant specified in rfc4122
+         *   110 Reserved, Microsoft backward compatibility
+         *   111 Reserved for future definition
+         * uint8_t node[6]
+         *
+         * For version 4, these bits are set/cleared:
+         * time_hi_and_version & 0x0fff | 0x4000
+         * clk_seq_and_variant & 0x3fff | 0x8000
+         */
+
+        i = open("/dev/urandom", O_RDONLY);
+        if (i >= 0) {
+                read(i, buf, 16);
+                close(i);
+        }
+        /* Paranoia. /dev/urandom may be missing.
+         * rand() is guaranteed to generate at least [0, 2^15) range,
          * but lowest bits in some libc are not so "random".  */
-        srand((unsigned)monotonic_us() + getpid());
-        for (i = 0; i < 16; i++)
-                buf[i] = rand() >> 5;
+        srand(monotonic_us());
+        pid = getpid();
+        while (1) {
+                for (i = 0; i < 16; i++)
+                        buf[i] ^= rand() >> 5;
+                if (pid == 0)
+                        break;
+                srand(pid);
+                pid = 0;
+        }
+
+        buf[4 + 2    ] = (buf[4 + 2    ] & 0x0f) | 0x40; /* time_hi_and_version */
+        buf[4 + 2 + 2] = (buf[4 + 2 + 2] & 0x3f) | 0x80; /* clk_seq_and_variant */
 
         bin2hex(uuid_string, (void*) buf, 16);
         /* f.e. UUID=dfd9c173-be52-4d27-99a5-c34c6c2ff55f */