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Better handle false positives. The MBR differs from the boot sector

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only because there's a partition table where the boot sector has
boot code. Boot sectors without boot code look like a MBR for all
practical purposes. This change adds a check for the partition table
and fails the probe when it's obvously invalid. The assumption being
that the sector contains a boot sector and not a MBR.
More checks are needed to distinguish a boot secto without boot code
from a (empty) MBR.
This commit is contained in:
Marcel Moolenaar 2008-02-28 22:30:41 +00:00
parent 2487d8f877
commit 6291ef2d80
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=176650
1 changed files with 24 additions and 6 deletions
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30
sys/geom/part/g_part_mbr.c
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@ -252,22 +252,42 @@ static int
g_part_mbr_probe(struct g_part_table *table, struct g_consumer *cp)
{
struct g_provider *pp;
u_char *buf;
int error, res;
u_char *buf, *p;
int error, index, res;
uint16_t magic;
pp = cp->provider;
/* Sanity-check the provider. */
if (pp->sectorsize < MBRSIZE || pp->mediasize < pp->sectorsize)
return (ENOSPC);
if (pp->sectorsize > 4096)
return (ENXIO);
/* Check that there's a MBR. */
buf = g_read_data(cp, 0L, pp->sectorsize, &error);
if (buf == NULL)
return (error);
res = le16dec(buf + DOSMAGICOFFSET);
/* We goto out on mismatch. */
res = ENXIO;
magic = le16dec(buf + DOSMAGICOFFSET);
if (magic != DOSMAGIC)
goto out;
for (index = 0; index < NDOSPART; index++) {
p = buf + DOSPARTOFF + index * DOSPARTSIZE;
if (p[0] != 0 && p[0] != 0x80)
goto out;
}
/* Match. */
res = G_PART_PROBE_PRI_NORM;
out:
g_free(buf);
return ((res == DOSMAGIC) ? G_PART_PROBE_PRI_NORM : ENXIO);
return (res);
}
static int
@ -305,8 +325,6 @@ g_part_mbr_read(struct g_part_table *basetable, struct g_consumer *cp)
ent.dp_size = le32dec(p + 12);
if (ent.dp_typ == 0 || ent.dp_typ == DOSPTYP_PMBR)
continue;
if (ent.dp_flag != 0 && ent.dp_flag != 0x80)
continue;
if (ent.dp_start == 0 || ent.dp_size == 0)
continue;
sectors = ent.dp_esect & 0x3f;