Newer Micro$oft operating systems (NT 3 and later) put a 4-byte
signature in the MBR at offset 440 decimal. Generate a random such
signature when creating a new disk label, and allow it to be changed.
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx>
---
fdisk/fdisk.c | 107 ++++++++++++++++++++++++++++++++++++++++++++++++++++-----
1 files changed, 98 insertions(+), 9 deletions(-)
diff --git a/fdisk/fdisk.c b/fdisk/fdisk.c
index 292b7a8..31449d6 100644
--- a/fdisk/fdisk.c
+++ b/fdisk/fdisk.c
@@ -91,7 +91,7 @@ store4_little_endian(unsigned char *cp, unsigned int val) {
}
static unsigned int
-read4_little_endian(unsigned char *cp) {
+read4_little_endian(const unsigned char *cp) {
return (unsigned int)(cp[0]) + ((unsigned int)(cp[1]) << 8)
+ ((unsigned int)(cp[2]) << 16)
+ ((unsigned int)(cp[3]) << 24);
@@ -117,6 +117,49 @@ get_nr_sects(struct partition *p) {
return read4_little_endian(p->size4);
}
+static ssize_t
+xread(int fd, void *buf, size_t count) {
+ char *p = buf;
+ ssize_t out = 0;
+ ssize_t rv;
+
+ while (count) {
+ rv = read(fd, p, count);
+ if (rv == -1) {
+ if (errno == EINTR || errno == EAGAIN)
+ continue;
+ return out ? out : -1; /* Error */
+ } else if (rv == 0) {
+ return out; /* EOF */
+ }
+
+ p += rv;
+ out += rv;
+ count -= rv;
+ }
+
+ return out;
+}
+
+static unsigned int
+get_random_id(void) {
+ int fd;
+ unsigned int v;
+ ssize_t rv = -1;
+
+ fd = open("/dev/urandom", O_RDONLY);
+ if (fd >= 0) {
+ rv = xread(fd, &v, sizeof v);
+ close(fd);
+ }
+
+ if (rv == sizeof v)
+ return v;
+
+ /* Fallback: sucks, but better than nothing */
+ return (unsigned int)(getpid() + time(NULL));
+}
+
/* normally O_RDWR, -l option gives O_RDONLY */
static int type_open = O_RDWR;
@@ -457,6 +500,7 @@ xmenu(void) {
puts(_(" f fix partition order")); /* !sun, !aix, !sgi */
puts(_(" g create an IRIX (SGI) partition table"));/* sgi */
puts(_(" h change number of heads"));
+ puts(_(" i change the disk identifier")); /* dos only */
puts(_(" m print this menu"));
puts(_(" p print the partition table"));
puts(_(" q quit without saving changes"));
@@ -720,25 +764,66 @@ read_extended(int ext) {
}
static void
+dos_write_mbr_id(unsigned char *b, unsigned int id) {
+ store4_little_endian(&b[440], id);
+}
+
+static unsigned int
+dos_read_mbr_id(const unsigned char *b) {
+ return read4_little_endian(&b[440]);
+}
+
+static void
+dos_print_mbr_id(void) {
+ printf(_("Disk identifier: 0x%08x\n"), dos_read_mbr_id(MBRbuffer));
+}
+
+static void
+dos_set_mbr_id(void) {
+ unsigned long new_id;
+ char *ep;
+ char ps[64];
+
+ snprintf(ps, sizeof ps, _("New disk identifier (current 0x%08x): "),
+ dos_read_mbr_id(MBRbuffer));
+
+ if (read_chars(ps) == '\n')
+ return;
+
+ new_id = strtoul(line_ptr, &ep, 0);
+ if (*ep != '\n')
+ return;
+
+ dos_write_mbr_id(MBRbuffer, new_id);
+ dos_print_mbr_id();
+}
+
+static void
create_doslabel(void) {
int i;
+ unsigned int id = get_random_id();
fprintf(stderr,
- _("Building a new DOS disklabel. Changes will remain in memory only,\n"
- "until you decide to write them. After that, of course, the previous\n"
- "content won't be recoverable.\n\n"));
+ _("Building a new DOS disklabel with disk identifier 0x%08x.\n"
+ "Changes will remain in memory only, until you decide to write them.\n"
+ "After that, of course, the previous content won't be recoverable.\n\n"),
+ id);
sun_nolabel(); /* otherwise always recognised as sun */
sgi_nolabel(); /* otherwise always recognised as sgi */
mac_label = aix_label = osf_label = possibly_osf_label = 0;
partitions = 4;
- for (i = 510-64; i < 510; i++)
- MBRbuffer[i] = 0;
- write_part_table_flag(MBRbuffer);
+ /* Zero out the MBR buffer */
extended_offset = 0;
set_all_unchanged();
set_changed(0);
get_boot(create_empty_dos);
+
+ /* Generate an MBR ID for this disk */
+ dos_write_mbr_id(MBRbuffer, id);
+
+ /* Mark it bootable (unfortunately required) */
+ write_part_table_flag(MBRbuffer);
}
#include <sys/utsname.h>
@@ -1528,9 +1613,12 @@ list_disk_geometry(void) {
printf(_(", total %llu sectors"),
total_number_of_sectors / (sector_size/512));
printf("\n");
- printf(_("Units = %s of %d * %d = %d bytes\n\n"),
+ printf(_("Units = %s of %d * %d = %d bytes\n"),
str_units(PLURAL),
units_per_sector, sector_size, units_per_sector * sector_size);
+ if (dos_label)
+ dos_print_mbr_id();
+ printf("\n");
}
/*
@@ -1695,7 +1783,6 @@ list_table(int xtra) {
printf(_("This doesn't look like a partition table\n"
"Probably you selected the wrong device.\n\n"));
}
-
/* Heuristic: we list partition 3 of /dev/foo as /dev/foo3,
but if the device name ends in a digit, say /dev/foo1,
@@ -2310,6 +2397,8 @@ xselect(void) {
case 'i':
if (sun_label)
sun_set_ilfact();
+ if (dos_label)
+ dos_set_mbr_id();
break;
case 'o':
if (sun_label)
--
1.5.2.2
-
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