159 lines
5.0 KiB
Diff
159 lines
5.0 KiB
Diff
From 70aa35b2b4d2e723fe82ac3184e5921a52be73ab Mon Sep 17 00:00:00 2001
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From: Jonathan Liu <net147@gmail.com>
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Date: Fri, 4 Oct 2013 07:32:12 -0700
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Subject: [PATCH 53/89] dos: improve MBR signature generation
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Using tv_usec in struct timeval from gettimeofday() doesn't provide
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enough precision to fill an unsigned 32-bit integer and isn't really
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random. It it always less than one million when using the GNU C library
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while an unsigned 32-bit integer ranges between 0 and 4294967295.
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In FAT filesystem creation, parted already uses a better random
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generator, so move that code into a common function and use it
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for MS-DOS MBR signature generation.
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* libparted/fs/r/fat/fat.c (_gen_new_serial_number): Remove.
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(fat_create): Use generate_random_uint32 instead of
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_gen_new_serial_number.
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* libparted/labels/dos.c (generate_random_id): Remove.
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(msdos_write): Use generate_random_uint32 instead of
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generate_random_id.
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* libparted/labels/misc.h (generate_random_uint32): New function.
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Created from _gen_new_serial_number in libparted/fs/r/fat/fat.c with
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additional check to avoid returning zero, which may be interpreted
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as no FAT serial number or no MBR signature.
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---
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NEWS | 4 ++++
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libparted/fs/r/fat/fat.c | 19 ++-----------------
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libparted/labels/dos.c | 12 +-----------
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libparted/labels/misc.h | 21 +++++++++++++++++++++
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4 files changed, 28 insertions(+), 28 deletions(-)
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diff --git a/NEWS b/NEWS
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index 98f7c6e..50faf4d 100644
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--- a/NEWS
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+++ b/NEWS
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@@ -23,6 +23,10 @@ GNU parted NEWS -*- outline -*-
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partprobe now tells the kernel to forget about any partitions
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on a device that has no recognizable partition table.
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+ dos: the range of random MBR signature values was artificially limited
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+ to 0..999999, which mistakenly included 0. Now, we use the full 32-bit
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+ range, but exclude 0.
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+
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** Changes in behavior
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parted -l no longer lists device-mapper devices other than
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diff --git a/libparted/fs/r/fat/fat.c b/libparted/fs/r/fat/fat.c
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index 2ab9279..c8e4552 100644
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--- a/libparted/fs/r/fat/fat.c
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+++ b/libparted/fs/r/fat/fat.c
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@@ -18,10 +18,10 @@
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#include <config.h>
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#include <string.h>
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-#include <uuid/uuid.h>
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#include "fat.h"
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#include "calc.h"
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+#include "../../../labels/misc.h"
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PedFileSystem*
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fat_alloc (const PedGeometry* geom)
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@@ -202,21 +202,6 @@ fat_root_dir_clear (PedFileSystem* fs)
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fs_info->root_dir_sector_count);
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}
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-/* hack: use the ext2 uuid library to generate a reasonably random (hopefully
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- * with /dev/random) number. Unfortunately, we can only use 4 bytes of it
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- */
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-static uint32_t
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-_gen_new_serial_number (void)
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-{
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- union {
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- uuid_t uuid;
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- uint32_t i;
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- } uu32;
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-
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- uuid_generate (uu32.uuid);
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- return uu32.i;
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-}
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-
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PedFileSystem*
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fat_create (PedGeometry* geom, FatType fat_type, PedTimer* timer)
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{
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@@ -316,7 +301,7 @@ fat_create (PedGeometry* geom, FatType fat_type, PedTimer* timer)
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return 0;
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}
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- fs_info->serial_number = _gen_new_serial_number ();
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+ fs_info->serial_number = generate_random_uint32 ();
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if (!fat_boot_sector_set_boot_code (&fs_info->boot_sector))
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goto error_free_buffers;
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diff --git a/libparted/labels/dos.c b/libparted/labels/dos.c
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index b8c161f..6bddd79 100644
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--- a/libparted/labels/dos.c
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+++ b/libparted/labels/dos.c
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@@ -1236,16 +1236,6 @@ write_extended_partitions (const PedDisk* disk)
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return write_empty_table (disk, ext_part->geom.start);
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}
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-static inline uint32_t generate_random_id (void)
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-{
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- struct timeval tv;
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- int rc;
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- rc = gettimeofday(&tv, NULL);
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- if (rc == -1)
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- return 0;
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- return (uint32_t)(tv.tv_usec & 0xFFFFFFFFUL);
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-}
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-
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static int
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msdos_write (const PedDisk* disk)
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{
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@@ -1267,7 +1257,7 @@ msdos_write (const PedDisk* disk)
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/* If there is no unique identifier, generate a random one */
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if (!table->mbr_signature)
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- table->mbr_signature = generate_random_id();
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+ table->mbr_signature = generate_random_uint32 ();
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memset (table->partitions, 0, sizeof (table->partitions));
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table->magic = PED_CPU_TO_LE16 (MSDOS_MAGIC);
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diff --git a/libparted/labels/misc.h b/libparted/labels/misc.h
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index c2ccea1..c039c5f 100644
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--- a/libparted/labels/misc.h
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+++ b/libparted/labels/misc.h
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@@ -16,6 +16,27 @@
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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+#include <inttypes.h>
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+#include <uuid/uuid.h>
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+
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+/* hack: use the ext2 uuid library to generate a reasonably random (hopefully
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+ * with /dev/random) number. Unfortunately, we can only use 4 bytes of it.
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+ * We make sure to avoid returning zero which may be interpreted as no FAT
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+ * serial number or no MBR signature.
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+ */
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+static inline uint32_t
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+generate_random_uint32 (void)
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+{
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+ union {
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+ uuid_t uuid;
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+ uint32_t i;
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+ } uu32;
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+
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+ uuid_generate (uu32.uuid);
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+
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+ return uu32.i > 0 ? uu32.i : 0xffffffff;
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+}
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+
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/* Return nonzero if FS_TYPE_NAME starts with "linux-swap".
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This must match the NUL-terminated "linux-swap" as well
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as "linux-swap(v0)" and "linux-swap(v1)". */
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--
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1.8.5.3
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