dos: improve MBR signature generation

Using tv_usec in struct timeval from gettimeofday() doesn't provide
enough precision to fill an unsigned 32-bit integer and isn't really
random. It it always less than one million when using the GNU C library
while an unsigned 32-bit integer ranges between 0 and 4294967295.

In FAT filesystem creation, parted already uses a better random
generator, so move that code into a common function and use it
for MS-DOS MBR signature generation.

* libparted/fs/r/fat/fat.c (_gen_new_serial_number): Remove.
(fat_create): Use generate_random_uint32 instead of
_gen_new_serial_number.
* libparted/labels/dos.c (generate_random_id): Remove.
(msdos_write): Use generate_random_uint32 instead of
generate_random_id.
* libparted/labels/misc.h (generate_random_uint32): New function.
Created from _gen_new_serial_number in libparted/fs/r/fat/fat.c with
additional check to avoid returning zero, which may be interpreted
as no FAT serial number or no MBR signature.

1 files changed, 2 insertions, 17 deletions

diff --git a/libparted/fs/r/fat/fat.c b/libparted/fs/r/fat/fat.c
index 2ab9279..c8e4552 100644
--- a/libparted/fs/r/fat/fat.c
+++ b/libparted/fs/r/fat/fat.c
@@ -18,10 +18,10 @@
 
 #include <config.h>
 #include <string.h>
-#include <uuid/uuid.h>
 
 #include "fat.h"
 #include "calc.h"
+#include "../../../labels/misc.h"
 
 PedFileSystem*
 fat_alloc (const PedGeometry* geom)
@@ -202,21 +202,6 @@ fat_root_dir_clear (PedFileSystem* fs)
 				   fs_info->root_dir_sector_count);
 }
 
-/* hack: use the ext2 uuid library to generate a reasonably random (hopefully
- * with /dev/random) number.  Unfortunately, we can only use 4 bytes of it
- */
-static uint32_t
-_gen_new_serial_number (void)
-{
-	union {
-		uuid_t uuid;
-		uint32_t i;
-	} uu32;
-
-	uuid_generate (uu32.uuid);
-	return uu32.i;
-}
-
 PedFileSystem*
 fat_create (PedGeometry* geom, FatType fat_type, PedTimer* timer)
 {
@@ -316,7 +301,7 @@ fat_create (PedGeometry* geom, FatType fat_type, PedTimer* timer)
 			return 0;
 	}
 
-	fs_info->serial_number = _gen_new_serial_number ();
+	fs_info->serial_number = generate_random_uint32 ();
 
 	if (!fat_boot_sector_set_boot_code (&fs_info->boot_sector))
 		goto error_free_buffers;