Better handle false positives. The MBR differs from the boot sector
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.
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6291ef2d80
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=176650
@ -252,22 +252,42 @@ static int
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g_part_mbr_probe(struct g_part_table *table, struct g_consumer *cp)
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{
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struct g_provider *pp;
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u_char *buf;
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int error, res;
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u_char *buf, *p;
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int error, index, res;
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uint16_t magic;
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pp = cp->provider;
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/* Sanity-check the provider. */
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if (pp->sectorsize < MBRSIZE || pp->mediasize < pp->sectorsize)
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return (ENOSPC);
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if (pp->sectorsize > 4096)
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return (ENXIO);
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/* Check that there's a MBR. */
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buf = g_read_data(cp, 0L, pp->sectorsize, &error);
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if (buf == NULL)
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return (error);
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res = le16dec(buf + DOSMAGICOFFSET);
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/* We goto out on mismatch. */
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res = ENXIO;
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magic = le16dec(buf + DOSMAGICOFFSET);
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if (magic != DOSMAGIC)
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goto out;
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for (index = 0; index < NDOSPART; index++) {
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p = buf + DOSPARTOFF + index * DOSPARTSIZE;
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if (p[0] != 0 && p[0] != 0x80)
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goto out;
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}
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/* Match. */
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res = G_PART_PROBE_PRI_NORM;
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out:
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g_free(buf);
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return ((res == DOSMAGIC) ? G_PART_PROBE_PRI_NORM : ENXIO);
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return (res);
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}
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static int
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@ -305,8 +325,6 @@ g_part_mbr_read(struct g_part_table *basetable, struct g_consumer *cp)
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ent.dp_size = le32dec(p + 12);
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if (ent.dp_typ == 0 || ent.dp_typ == DOSPTYP_PMBR)
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continue;
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if (ent.dp_flag != 0 && ent.dp_flag != 0x80)
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continue;
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if (ent.dp_start == 0 || ent.dp_size == 0)
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continue;
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sectors = ent.dp_esect & 0x3f;
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