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denyhosts/clamav/libclamav/mbr.c

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/*
* Copyright (C) 2014-2022 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
*
* Authors: Kevin Lin <klin@sourcefire.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
* MA 02110-1301, USA.
*/
#if HAVE_CONFIG_H
#include "clamav-config.h"
#endif
#include <stdio.h>
#include <errno.h>
#if HAVE_STRING_H
#include <string.h>
#endif
#include <ctype.h>
#include <fcntl.h>
#include <zlib.h>
#include "clamav.h"
#include "others.h"
#include "mbr.h"
#include "partition_intersection.h"
#include "scanners.h"
#include "dconf.h"
//#define DEBUG_MBR_PARSE
//#define DEBUG_EBR_PARSE
#ifdef DEBUG_MBR_PARSE
#define mbr_parsemsg(...) cli_dbgmsg(__VA_ARGS__)
#else
#define mbr_parsemsg(...) ;
#endif
#ifdef DEBUG_EBR_PARSE
#define ebr_parsemsg(...) cli_dbgmsg(__VA_ARGS__)
#else
#define ebr_parsemsg(...) ;
#endif
enum MBR_STATE {
SEEN_NOTHING,
SEEN_PARTITION,
SEEN_EXTENDED,
SEEN_EMPTY
};
static cl_error_t mbr_scanextprtn(cli_ctx *ctx, unsigned *prtncount, size_t extlba,
size_t extlbasize, size_t sectorsize);
static cl_error_t mbr_check_mbr(struct mbr_boot_record *record, size_t maplen, size_t sectorsize);
static cl_error_t mbr_check_ebr(struct mbr_boot_record *record);
static cl_error_t mbr_primary_partition_intersection(cli_ctx *ctx, struct mbr_boot_record mbr, size_t sectorsize);
static cl_error_t mbr_extended_partition_intersection(cli_ctx *ctx, unsigned *prtncount, size_t extlba, size_t sectorsize);
cl_error_t cli_mbr_check(const unsigned char *buff, size_t len, size_t maplen)
{
struct mbr_boot_record mbr;
size_t mbr_base = 0;
size_t sectorsize = 512;
if (len < sectorsize) {
return CL_EFORMAT;
}
mbr_base = sectorsize - sizeof(struct mbr_boot_record);
memcpy(&mbr, buff + mbr_base, sizeof(mbr));
mbr_convert_to_host(&mbr);
if ((mbr.entries[0].type == MBR_PROTECTIVE) || (mbr.entries[0].type == MBR_HYBRID))
return CL_TYPE_GPT;
return mbr_check_mbr(&mbr, maplen, sectorsize);
}
cl_error_t cli_mbr_check2(cli_ctx *ctx, size_t sectorsize)
{
struct mbr_boot_record mbr;
size_t pos = 0, mbr_base = 0;
size_t maplen;
if (!ctx || !ctx->fmap) {
cli_errmsg("cli_scanmbr: Invalid context\n");
return CL_ENULLARG;
}
/* sector size calculation, actual value is OS dependent */
if (sectorsize == 0)
sectorsize = MBR_SECTOR_SIZE;
mbr_base = sectorsize - sizeof(struct mbr_boot_record);
/* size of total file must be a multiple of the sector size */
maplen = ctx->fmap->len;
if ((maplen % sectorsize) != 0) {
cli_dbgmsg("cli_scanmbr: File sized %lu is not a multiple of sector size %lu\n",
(unsigned long)maplen, (unsigned long)sectorsize);
return CL_EFORMAT;
}
/* sector 0 (first sector) is the master boot record */
pos = (MBR_SECTOR * sectorsize) + mbr_base;
/* read the master boot record */
if (fmap_readn(ctx->fmap, &mbr, pos, sizeof(mbr)) != sizeof(mbr)) {
cli_dbgmsg("cli_scanmbr: Invalid master boot record\n");
return CL_EFORMAT;
}
/* convert the little endian to host, include the internal */
mbr_convert_to_host(&mbr);
if ((mbr.entries[0].type == MBR_PROTECTIVE) || (mbr.entries[0].type == MBR_HYBRID))
return CL_TYPE_GPT;
return mbr_check_mbr(&mbr, maplen, sectorsize);
}
/* sets sectorsize to default value if specified to be 0 */
cl_error_t cli_scanmbr(cli_ctx *ctx, size_t sectorsize)
{
cl_error_t status = CL_SUCCESS;
struct mbr_boot_record mbr;
enum MBR_STATE state = SEEN_NOTHING;
size_t pos = 0, mbr_base = 0, partoff = 0;
unsigned i = 0, prtncount = 0;
size_t maplen, partsize;
mbr_parsemsg("The start of something magnificant: MBR parsing\n");
if (!ctx || !ctx->fmap) {
cli_errmsg("cli_scanmbr: Invalid context\n");
status = CL_ENULLARG;
goto done;
}
/* sector size calculation, actual value is OS dependent */
if (sectorsize == 0)
sectorsize = MBR_SECTOR_SIZE;
mbr_base = sectorsize - sizeof(struct mbr_boot_record);
/* size of total file must be a multiple of the sector size */
maplen = ctx->fmap->len;
if ((maplen % sectorsize) != 0) {
cli_dbgmsg("cli_scanmbr: File sized %lu is not a multiple of sector size %lu\n",
(unsigned long)maplen, (unsigned long)sectorsize);
status = CL_EFORMAT;
goto done;
}
/* sector 0 (first sector) is the master boot record */
pos = (MBR_SECTOR * sectorsize) + mbr_base;
/* read the master boot record */
if (fmap_readn(ctx->fmap, &mbr, pos, sizeof(mbr)) != sizeof(mbr)) {
cli_dbgmsg("cli_scanmbr: Invalid master boot record\n");
status = CL_EFORMAT;
goto done;
}
/* convert the little endian to host, include the internal */
mbr_convert_to_host(&mbr);
/* MBR checks */
status = mbr_check_mbr(&mbr, maplen, sectorsize);
if (status != CL_SUCCESS) {
status = status;
goto done;
}
/* MBR is valid, examine bootstrap code */
status = cli_magic_scan_nested_fmap_type(ctx->fmap, 0, sectorsize, ctx, CL_TYPE_ANY, NULL, LAYER_ATTRIBUTES_NONE);
if (status != CL_SUCCESS) {
status = status;
goto done;
}
/* check that the partition table has no intersections - HEURISTICS */
if (SCAN_HEURISTIC_PARTITION_INTXN && (ctx->dconf->other & OTHER_CONF_PRTNINTXN)) {
status = mbr_primary_partition_intersection(ctx, mbr, sectorsize);
if (status != CL_SUCCESS) {
status = status;
goto done;
}
}
/* MBR is valid, examine partitions */
prtncount = 0;
cli_dbgmsg("MBR Signature: %x\n", mbr.signature);
for (i = 0; i < MBR_MAX_PARTITION_ENTRIES && prtncount < ctx->engine->maxpartitions; ++i) {
cli_dbgmsg("MBR Partition Entry %u:\n", i);
cli_dbgmsg("Status: %u\n", mbr.entries[i].status);
cli_dbgmsg("Type: %x\n", mbr.entries[i].type);
cli_dbgmsg("Blocks: [%u, +%u), ([%zu, +%zu))\n",
mbr.entries[i].firstLBA, mbr.entries[i].numLBA,
mbr.entries[i].firstLBA * sectorsize,
mbr.entries[i].numLBA * sectorsize);
/* Handle MBR entry based on type */
if (mbr.entries[i].type == MBR_EMPTY) {
/* empty partition entry */
prtncount++;
} else if (mbr.entries[i].type == MBR_EXTENDED) {
if (state == SEEN_EXTENDED) {
cli_dbgmsg("cli_scanmbr: detected a master boot record "
"with multiple extended partitions\n");
}
state = SEEN_EXTENDED; /* used only to detect multiple extended partitions */
status = mbr_scanextprtn(ctx, &prtncount, mbr.entries[i].firstLBA,
mbr.entries[i].numLBA, sectorsize);
if (status != CL_SUCCESS) {
status = status;
goto done;
}
} else {
prtncount++;
partoff = mbr.entries[i].firstLBA * sectorsize;
partsize = mbr.entries[i].numLBA * sectorsize;
mbr_parsemsg("cli_magic_scan_nested_fmap_type: [%u, +%u)\n", partoff, partsize);
status = cli_magic_scan_nested_fmap_type(ctx->fmap, partoff, partsize, ctx, CL_TYPE_PART_ANY, NULL, LAYER_ATTRIBUTES_NONE);
if (status != CL_SUCCESS) {
status = status;
goto done;
}
}
}
if (prtncount >= ctx->engine->maxpartitions) {
cli_dbgmsg("cli_scanmbr: maximum partitions reached\n");
}
done:
return status;
}
static cl_error_t mbr_scanextprtn(cli_ctx *ctx, unsigned *prtncount, size_t extlba, size_t extlbasize, size_t sectorsize)
{
cl_error_t status = CL_CLEAN;
struct mbr_boot_record ebr;
enum MBR_STATE state = SEEN_NOTHING;
size_t pos = 0, mbr_base = 0, logiclba = 0, extoff = 0, partoff = 0;
size_t partsize, extsize;
unsigned i = 0, j = 0;
ebr_parsemsg("The start of something exhausting: EBR parsing\n");
mbr_base = sectorsize - sizeof(struct mbr_boot_record);
logiclba = 0;
extoff = extlba * sectorsize;
extsize = extlbasize * sectorsize;
do {
pos = extlba * sectorsize; /* start of extended partition */
/* read the extended boot record */
pos += (logiclba * sectorsize) + mbr_base;
if (fmap_readn(ctx->fmap, &ebr, pos, sizeof(ebr)) != sizeof(ebr)) {
cli_dbgmsg("cli_scanebr: Invalid extended boot record\n");
status = CL_EFORMAT;
goto done;
}
/* convert the little endian to host */
mbr_convert_to_host(&ebr);
/* EBR checks */
status = mbr_check_ebr(&ebr);
if (status != CL_SUCCESS) {
status = status;
goto done;
}
/* update state */
state = SEEN_NOTHING;
(*prtncount)++;
/* EBR is valid, examine partitions */
cli_dbgmsg("EBR Partition Entry %u:\n", i++);
cli_dbgmsg("EBR Signature: %x\n", ebr.signature);
for (j = 0; j < MBR_MAX_PARTITION_ENTRIES; ++j) {
if (j < 2) {
cli_dbgmsg("Logical Partition Entry %u:\n", j);
cli_dbgmsg("Status: %u\n", ebr.entries[j].status);
cli_dbgmsg("Type: %x\n", ebr.entries[j].type);
cli_dbgmsg("Blocks: [%u, +%u), ([%lu, +%lu))\n",
ebr.entries[j].firstLBA, ebr.entries[j].numLBA,
(unsigned long)(ebr.entries[j].firstLBA * sectorsize),
(unsigned long)(ebr.entries[j].numLBA * sectorsize));
if (ebr.entries[j].type == MBR_EMPTY) {
/* empty partition entry */
switch (state) {
case SEEN_NOTHING:
state = SEEN_EMPTY;
break;
case SEEN_PARTITION:
logiclba = 0;
break;
case SEEN_EMPTY:
logiclba = 0;
/* fall-through */
case SEEN_EXTENDED:
cli_warnmsg("cli_scanebr: detected a logical boot record "
"without a partition record\n");
break;
default:
cli_warnmsg("cli_scanebr: undefined state for EBR parsing\n");
status = CL_EPARSE;
goto done;
}
} else if (ebr.entries[j].type == MBR_EXTENDED) {
switch (state) {
case SEEN_NOTHING:
state = SEEN_EXTENDED;
break;
case SEEN_PARTITION:
break;
case SEEN_EMPTY:
cli_warnmsg("cli_scanebr: detected a logical boot record "
"without a partition record\n");
break;
case SEEN_EXTENDED:
cli_warnmsg("cli_scanebr: detected a logical boot record "
"with multiple extended partition records\n");
status = CL_EFORMAT;
goto done;
default:
cli_dbgmsg("cli_scanebr: undefined state for EBR parsing\n");
status = CL_EPARSE;
goto done;
}
logiclba = ebr.entries[j].firstLBA;
} else {
switch (state) {
case SEEN_NOTHING:
state = SEEN_PARTITION;
break;
case SEEN_PARTITION:
cli_warnmsg("cli_scanebr: detected a logical boot record "
"with multiple partition records\n");
logiclba = 0; /* no extended partitions are possible */
break;
case SEEN_EXTENDED:
cli_warnmsg("cli_scanebr: detected a logical boot record "
"with extended partition record first\n");
break;
case SEEN_EMPTY:
cli_warnmsg("cli_scanebr: detected a logical boot record "
"with empty partition record first\n");
logiclba = 0; /* no extended partitions are possible */
break;
default:
cli_dbgmsg("cli_scanebr: undefined state for EBR parsing\n");
status = CL_EPARSE;
goto done;
}
partoff = (extlba + logiclba + ebr.entries[j].firstLBA) * sectorsize;
partsize = ebr.entries[j].numLBA * sectorsize;
if (partoff + partsize > extoff + extsize) {
cli_dbgmsg("cli_scanebr: Invalid extended partition entry\n");
status = CL_EFORMAT;
goto done;
}
status = cli_magic_scan_nested_fmap_type(ctx->fmap, partoff, partsize, ctx, CL_TYPE_PART_ANY, NULL, LAYER_ATTRIBUTES_NONE);
if (status != CL_SUCCESS) {
status = status;
goto done;
}
}
} else {
/* check the last two entries to be empty */
if (ebr.entries[j].type != MBR_EMPTY) {
cli_dbgmsg("cli_scanebr: detected a non-empty partition "
"entry at index %u\n",
j);
/* should we attempt to use these entries? */
status = CL_EFORMAT;
goto done;
}
}
}
} while (logiclba != 0 && (*prtncount) < ctx->engine->maxpartitions);
cli_dbgmsg("cli_scanmbr: examined %u logical partitions\n", i);
done:
return status;
}
void mbr_convert_to_host(struct mbr_boot_record *record)
{
struct mbr_partition_entry *entry;
unsigned i;
for (i = 0; i < MBR_MAX_PARTITION_ENTRIES; ++i) {
entry = &record->entries[i];
entry->firstLBA = le32_to_host(entry->firstLBA);
entry->numLBA = le32_to_host(entry->numLBA);
}
record->signature = be16_to_host(record->signature);
}
static cl_error_t mbr_check_mbr(struct mbr_boot_record *record, size_t maplen, size_t sectorsize)
{
cl_error_t status = CL_SUCCESS;
unsigned i = 0;
size_t partoff = 0;
size_t partsize = 0;
for (i = 0; i < MBR_MAX_PARTITION_ENTRIES; ++i) {
/* check status */
if ((record->entries[i].status != MBR_STATUS_INACTIVE) &&
(record->entries[i].status != MBR_STATUS_ACTIVE)) {
cli_dbgmsg("cli_scanmbr: Invalid boot record status\n");
status = CL_EFORMAT;
goto done;
}
partoff = record->entries[i].firstLBA * sectorsize;
partsize = record->entries[i].numLBA * sectorsize;
if (partoff + partsize > maplen) {
cli_dbgmsg("cli_scanmbr: Invalid partition entry\n");
status = CL_EFORMAT;
goto done;
}
}
/* check the signature */
if (record->signature != MBR_SIGNATURE) {
cli_dbgmsg("cli_scanmbr: Invalid boot record signature\n");
status = CL_EFORMAT;
goto done;
}
/* check the maplen */
if ((maplen / sectorsize) < 2) {
cli_dbgmsg("cli_scanmbr: bootstrap code or file is too small to hold disk image\n");
status = CL_EFORMAT;
goto done;
}
done:
return status;
}
static cl_error_t mbr_check_ebr(struct mbr_boot_record *record)
{
cl_error_t status = CL_SUCCESS;
unsigned i = 0;
for (i = 0; i < MBR_MAX_PARTITION_ENTRIES - 2; ++i) {
/* check status */
if ((record->entries[i].status != MBR_STATUS_INACTIVE) &&
(record->entries[i].status != MBR_STATUS_ACTIVE)) {
cli_dbgmsg("cli_scanmbr: Invalid boot record status\n");
status = CL_EFORMAT;
goto done;
}
}
/* check the signature */
if (record->signature != MBR_SIGNATURE) {
cli_dbgmsg("cli_scanmbr: Invalid boot record signature\n");
status = CL_EFORMAT;
goto done;
}
done:
return status;
}
/* this includes the overall bounds of extended partitions */
static cl_error_t mbr_primary_partition_intersection(cli_ctx *ctx, struct mbr_boot_record mbr, size_t sectorsize)
{
cl_error_t status = CL_CLEAN;
cl_error_t ret;
partition_intersection_list_t prtncheck;
unsigned i = 0, pitxn = 0, prtncount = 0;
partition_intersection_list_init(&prtncheck);
for (i = 0; i < MBR_MAX_PARTITION_ENTRIES && prtncount < ctx->engine->maxpartitions; ++i) {
if (mbr.entries[i].type == MBR_EMPTY) {
/* empty partition entry */
prtncount++;
} else {
ret = partition_intersection_list_check(&prtncheck, &pitxn, mbr.entries[i].firstLBA,
mbr.entries[i].numLBA);
if (ret != CL_CLEAN) {
if (ret == CL_VIRUS) {
cli_dbgmsg("cli_scanmbr: detected intersection with partitions "
"[%u, %u]\n",
pitxn, i);
status = cli_append_potentially_unwanted(ctx, "Heuristics.MBRPartitionnIntersect");
if (status != CL_SUCCESS) {
goto done;
}
} else {
status = ret;
goto done;
}
}
if (mbr.entries[i].type == MBR_EXTENDED) {
/* check the logical partitions */
ret = mbr_extended_partition_intersection(ctx, &prtncount,
mbr.entries[i].firstLBA, sectorsize);
if (ret != CL_SUCCESS) {
status = ret;
goto done;
}
} else {
prtncount++;
}
}
}
done:
partition_intersection_list_free(&prtncheck);
return status;
}
/* checks internal logical partitions */
static cl_error_t mbr_extended_partition_intersection(cli_ctx *ctx, unsigned *prtncount, size_t extlba, size_t sectorsize)
{
cl_error_t status = CL_CLEAN;
cl_error_t ret;
struct mbr_boot_record ebr;
partition_intersection_list_t prtncheck;
unsigned i, pitxn;
int mbr_base = 0;
size_t pos = 0, logiclba = 0;
mbr_base = sectorsize - sizeof(struct mbr_boot_record);
partition_intersection_list_init(&prtncheck);
logiclba = 0;
i = 0;
do {
pos = extlba * sectorsize; /* start of extended partition */
/* read the extended boot record */
pos += (logiclba * sectorsize) + mbr_base;
if (fmap_readn(ctx->fmap, &ebr, pos, sizeof(ebr)) != sizeof(ebr)) {
cli_dbgmsg("cli_scanebr: Invalid extended boot record\n");
partition_intersection_list_free(&prtncheck);
status = CL_EFORMAT;
goto done;
}
/* convert the little endian to host */
mbr_convert_to_host(&ebr);
/* update state */
(*prtncount)++;
/* assume that logical record is first and extended is second */
ret = partition_intersection_list_check(&prtncheck, &pitxn, logiclba, ebr.entries[0].numLBA);
if (ret != CL_CLEAN) {
if (ret == CL_VIRUS) {
cli_dbgmsg("cli_scanebr: detected intersection with partitions "
"[%u, %u]\n",
pitxn, i);
status = cli_append_potentially_unwanted(ctx, "Heuristics.MBRPartitionnIntersect");
if (status == CL_VIRUS) {
goto done;
}
} else {
status = ret;
goto done;
}
}
/* assume extended is second entry */
if (ebr.entries[1].type != MBR_EXTENDED) {
cli_dbgmsg("cli_scanebr: second entry for EBR is not an extended partition\n");
break;
}
logiclba = ebr.entries[1].firstLBA;
++i;
} while (logiclba != 0 && (*prtncount) < ctx->engine->maxpartitions);
done:
partition_intersection_list_free(&prtncheck);
return status;
}
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