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Use genhash_pe instead of checkfp_pe for section hash computation

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cli_checkfp_pe is now effectively the function that just checks
the Authenticode hash.  This makes the code less complicated,
and adds some minor improvements:
 - section hashes are no longer computed if there is no stats
   callback function (at least in that part of the code)
 - We now actually set the len field in the stats_section_t
   structure
 - If an error occurs when computing a section hash, we skip
   that section instead of not computing any hashes
This commit is contained in:
Andrew 2019-02-04 18:48:22 -05:00 • committed by Micah Snyder
parent ef24839531
commit 14d52d0c63
4 changed files with 102 additions and 133 deletions
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31
libclamav/matcher.c
View file

@ -567,7 +567,6 @@ int cli_checkfp_virus(unsigned char *digest, size_t size, cli_ctx *ctx, const ch
uint8_t shash1[SHA1_HASH_SIZE * 2 + 1];
uint8_t shash256[SHA256_HASH_SIZE * 2 + 1];
int have_sha1, have_sha256, do_dsig_check = 1;
stats_section_t sections;
if (cli_hm_scan(digest, size, &virname, ctx->engine->hm_fp, CLI_HASH_MD5) == CL_VIRUS) {
cli_dbgmsg("cli_checkfp(md5): Found false positive detection (fp sig: %s), size: %d\n", virname, (int)size);
@ -585,6 +584,8 @@ int cli_checkfp_virus(unsigned char *digest, size_t size, cli_ctx *ctx, const ch
vname ? vname : "Name");
}
// TODO Replace this with the ability to actually perform detection with
// the blacklisted sig entries
if (vname)
do_dsig_check = strncmp("W32S.", vname, 5);
@ -652,17 +653,10 @@ int cli_checkfp_virus(unsigned char *digest, size_t size, cli_ctx *ctx, const ch
}
#endif
memset(&sections, 0x00, sizeof(stats_section_t));
if (do_dsig_check || ctx->engine->cb_stats_add_sample) {
uint32_t flags = (do_dsig_check ? CL_CHECKFP_PE_FLAG_AUTHENTICODE : 0);
if (!(ctx->engine->engine_options & ENGINE_OPTIONS_DISABLE_PE_STATS) && !(ctx->engine->dconf->stats & (DCONF_STATS_DISABLED | DCONF_STATS_PE_SECTION_DISABLED)))
flags |= CL_CHECKFP_PE_FLAG_STATS;
switch (cli_checkfp_pe(ctx, &sections, flags)) {
if (do_dsig_check) {
switch (cli_checkfp_pe(ctx)) {
case CL_CLEAN:
cli_dbgmsg("cli_checkfp(pe): PE file whitelisted due to valid digital signature\n");
if (sections.sections)
free(sections.sections);
return CL_CLEAN;
default:
break;
@ -672,11 +666,22 @@ int cli_checkfp_virus(unsigned char *digest, size_t size, cli_ctx *ctx, const ch
if (ctx->engine->cb_hash)
ctx->engine->cb_hash(fmap_fd(*ctx->fmap), size, (const unsigned char *)md5, vname ? vname : "noname", ctx->cb_ctx);
if (ctx->engine->cb_stats_add_sample)
if (ctx->engine->cb_stats_add_sample) {
stats_section_t sections;
memset(&sections, 0x00, sizeof(stats_section_t));
if (!(ctx->engine->engine_options & ENGINE_OPTIONS_DISABLE_PE_STATS) &&
!(ctx->engine->dconf->stats & (DCONF_STATS_DISABLED | DCONF_STATS_PE_SECTION_DISABLED)))
cli_genhash_pe(ctx, CL_GENHASH_PE_CLASS_SECTION, 1, &sections);
// TODO We probably only want to call cb_stats_add_sample when
// sections.section != NULL... leaving as is for now
ctx->engine->cb_stats_add_sample(vname ? vname : "noname", digest, size, &sections, ctx->engine->stats_data);
if (sections.sections)
free(sections.sections);
if (sections.sections) {
free(sections.sections);
}
}
return CL_VIRUS;
}

191
libclamav/pe.c
View file

@ -5508,29 +5508,8 @@ static int sort_sects(const void *first, const void *second)
* CL_CLEAN will be returned if the file was whitelisted based on its
* signature. CL_VIRUS will be returned if the file was blacklisted based on
* its signature. Otherwise, an cl_error_t error value will be returned.
*
* Also, this function computes the hashes of each section (sorted based on the
* RVAs of the sections) if the CL_CHECKFP_PE_FLAG_STATS flag exists in flags
*
* TODO The code to compute the section hashes is copied from
* cli_genhash_pe - we should use that function instead where this
* functionality is needed, since we no longer need to compute the section
* hashes as part of the authenticode hash calculation.
*
* If the section hashes are to be computed and returned, this function
* allocates memory for the section hashes, and it's up to the caller to free
* it. hashes->sections will be initialized to NULL at the beginning of the
* function, and if after the call it's value is non-NULL, the memory should be
* freed. Furthermore, if hashes->sections is non-NULL, the hashes can assume
* to be valid regardless of the return code.
*
* Also, a few other notes:
* - If a section has a virtual size of zero, it's corresponding hash value
* will not be computed and the hash contents will be all zeroes.
* - TODO Instead of not providing back any hashes when an invalid section is
* encountered, would it be better to still compute hashes for the valid
* sections? */
cl_error_t cli_checkfp_pe(cli_ctx *ctx, stats_section_t *hashes, uint32_t flags)
*/
cl_error_t cli_checkfp_pe(cli_ctx *ctx)
{
size_t at;
unsigned int i, hlen;
@ -5554,15 +5533,6 @@ cl_error_t cli_checkfp_pe(cli_ctx *ctx, stats_section_t *hashes, uint32_t flags)
if (!(DCONF & PE_CONF_CATALOG))
return CL_EFORMAT;
if (flags == CL_CHECKFP_PE_FLAG_NONE)
return CL_BREAK;
if (flags & CL_CHECKFP_PE_FLAG_STATS) {
if (!(hashes))
return CL_ENULLARG;
hashes->sections = NULL;
}
// TODO see if peinfo can be passed in (or lives in ctx or something) and
// if so, use that to avoid having to re-parse the header
cli_exe_info_init(peinfo, 0);
@ -5579,68 +5549,12 @@ cl_error_t cli_checkfp_pe(cli_ctx *ctx, stats_section_t *hashes, uint32_t flags)
// the section hashes), bail out if we don't have any Authenticode hashes
// loaded from .cat files
if (sec_dir_size < 8 && !cli_hm_have_size(ctx->engine->hm_fp, CLI_HASH_SHA1, 2)) {
if (flags & CL_CHECKFP_PE_FLAG_STATS) {
/* If stats is enabled, continue parsing the sample */
flags ^= CL_CHECKFP_PE_FLAG_AUTHENTICODE;
} else {
cli_exe_info_destroy(peinfo);
return CL_BREAK;
}
cli_exe_info_destroy(peinfo);
return CL_BREAK;
}
fsize = map->len;
if (flags & CL_CHECKFP_PE_FLAG_STATS) {
hashes->nsections = peinfo->nsections;
hashes->sections = cli_calloc(peinfo->nsections, sizeof(struct cli_section_hash));
;
if (!(hashes->sections)) {
cli_exe_info_destroy(peinfo);
return CL_EMEM;
}
}
#define free_section_hashes() \
do { \
if (flags & CL_CHECKFP_PE_FLAG_STATS) { \
free(hashes->sections); \
hashes->sections = NULL; \
} \
} while (0)
// TODO This likely isn't needed anymore, since we no longer compute
// the authenticode hash like the 2008 spec doc says (sort sections
// and use the section info to compute the hash)
cli_qsort(peinfo->sections, peinfo->nsections, sizeof(*peinfo->sections), sort_sects);
/* Hash the sections */
if (flags & CL_CHECKFP_PE_FLAG_STATS) {
for (i = 0; i < peinfo->nsections; i++) {
const uint8_t *hptr;
void *md5ctx;
if (!peinfo->sections[i].rsz)
continue;
if (!(hptr = fmap_need_off_once(map, peinfo->sections[i].raw, peinfo->sections[i].rsz))) {
cli_exe_info_destroy(peinfo);
free_section_hashes();
return CL_EFORMAT;
}
md5ctx = cl_hash_init("md5");
if (md5ctx) {
cl_update_hash(md5ctx, (void *)hptr, peinfo->sections[i].rsz);
cl_finish_hash(md5ctx, hashes->sections[i].md5);
}
}
}
/* After this point it's the caller's responsibility to free
* hashes->sections. Also, in the case where we are just computing the
* stats, we are finished */
while (flags & CL_CHECKFP_PE_FLAG_AUTHENTICODE) {
do {
// We'll build a list of the regions that need to be hashed and pass it to
// asn1_check_mscat to do hash verification there (the hash algorithm is
// specified in the PKCS7 structure). We need to hash up to 4 regions
@ -5651,13 +5565,11 @@ cl_error_t cli_checkfp_pe(cli_ctx *ctx, stats_section_t *hashes, uint32_t flags)
}
nregions = 0;
#define add_chunk_to_hash_list(_offset, _size) \
do { \
if (flags & CL_CHECKFP_PE_FLAG_AUTHENTICODE) { \
regions[nregions].offset = (_offset); \
regions[nregions].size = (_size); \
nregions++; \
} \
#define add_chunk_to_hash_list(_offset, _size) \
do { \
regions[nregions].offset = (_offset); \
regions[nregions].size = (_size); \
nregions++; \
} while (0)
// Pretty much every case below should return CL_EFORMAT
@ -5802,7 +5714,8 @@ cl_error_t cli_checkfp_pe(cli_ctx *ctx, stats_section_t *hashes, uint32_t flags)
ret = CL_EVERIFY;
break;
} /* while(flags & CL_CHECKFP_PE_FLAG_AUTHENTICODE) */
} while (0);
if (NULL != hashctx) {
cl_hash_destroy(hashctx);
@ -5816,7 +5729,26 @@ cl_error_t cli_checkfp_pe(cli_ctx *ctx, stats_section_t *hashes, uint32_t flags)
return ret;
}
int cli_genhash_pe(cli_ctx *ctx, unsigned int class, int type)
/* Print out either the MD5, SHA1, or SHA256 associated with the imphash or
* the individual sections. Also, this function computes the hashes of each
* section (sorted based on the RVAs of the sections) if hashes is non-NULL.
*
* If the section hashes are to be computed and returned, this function
* allocates memory for the section hashes, and it's up to the caller to free
* it. hashes->sections will be initialized to NULL at the beginning of the
* function, and if after the call it's value is non-NULL, the memory should be
* freed. Furthermore, if hashes->sections is non-NULL, the hashes can assume
* to be valid regardless of the return code.
*
* Also, a few other notes:
* - If a section has a virtual size of zero, it's corresponding hash value
* will not be computed and the hash contents will be all zeroes.
* - If a section extends beyond the end of the file, the section data and
* length will be truncated, and the hash generated accordingly
* - If a section exists completely outside of the file, it won't be included
* in the list of sections, and nsections will be adjusted accordingly.
*/
int cli_genhash_pe(cli_ctx *ctx, unsigned int class, int type, stats_section_t *hashes)
{
unsigned int i;
struct cli_exe_info _peinfo;
@ -5826,9 +5758,20 @@ int cli_genhash_pe(cli_ctx *ctx, unsigned int class, int type)
int genhash[CLI_HASH_AVAIL_TYPES];
int hlen = 0;
if (hashes) {
hashes->sections = NULL;
if (class != CL_GENHASH_PE_CLASS_SECTION || type != 1) {
cli_dbgmsg("`hashes` can only be populated with MD5 PE section data\n");
return CL_EARG;
}
}
if (class >= CL_GENHASH_PE_CLASS_LAST)
return CL_EARG;
// TODO see if peinfo can be passed in (or lives in ctx or something) and
// if so, use that to avoid having to re-parse the header
cli_exe_info_init(peinfo, 0);
if (cli_peheader(*ctx->fmap, peinfo, CLI_PEHEADER_OPT_NONE, NULL) != CLI_PEHEADER_RET_SUCCESS) {
@ -5864,35 +5807,54 @@ int cli_genhash_pe(cli_ctx *ctx, unsigned int class, int type)
return CL_EMEM;
}
if (hashes) {
hashes->nsections = peinfo->nsections;
hashes->sections = cli_calloc(peinfo->nsections, sizeof(struct cli_section_hash));
if (!(hashes->sections)) {
cli_exe_info_destroy(peinfo);
free(hash);
return CL_EMEM;
}
}
if (class == CL_GENHASH_PE_CLASS_SECTION) {
char *dstr = NULL;
char *dstr;
for (i = 0; i < peinfo->nsections; i++) {
/* Generate hashes */
if (cli_hashsect(*ctx->fmap, &peinfo->sections[i], hashset, genhash, genhash) == 1) {
dstr = cli_str2hex((char *)hash, hlen);
cli_dbgmsg("Section{%u}: %u:%s\n", i, peinfo->sections[i].rsz, dstr ? (char *)dstr : "(NULL)");
if (dstr != NULL) {
free(dstr);
dstr = NULL;
if (cli_debug_flag) {
dstr = cli_str2hex((char *)hash, hlen);
cli_dbgmsg("Section{%u}: %u:%s\n", i, peinfo->sections[i].rsz, dstr ? (char *)dstr : "(NULL)");
if (dstr != NULL) {
free(dstr);
}
}
} else {
if (hashes) {
memcpy(hashes->sections[i].md5, hash, sizeof(hashes->sections[i].md5));
hashes->sections[i].len = peinfo->sections[i].rsz;
}
} else if (peinfo->sections[i].rsz) {
cli_dbgmsg("Section{%u}: failed to generate hash for section\n", i);
} else {
cli_dbgmsg("Section{%u}: section contains no data\n", i);
}
}
} else if (class == CL_GENHASH_PE_CLASS_IMPTBL) {
char *dstr = NULL;
char *dstr;
uint32_t impsz = 0;
int ret;
/* Generate hash */
ret = hash_imptbl(ctx, hashset, &impsz, genhash, peinfo);
if (ret == CL_SUCCESS) {
dstr = cli_str2hex((char *)hash, hlen);
cli_dbgmsg("Imphash: %s:%u\n", dstr ? (char *)dstr : "(NULL)", impsz);
if (dstr != NULL) {
free(dstr);
dstr = NULL;
if (cli_debug_flag) {
dstr = cli_str2hex((char *)hash, hlen);
cli_dbgmsg("Imphash: %s:%u\n", dstr ? (char *)dstr : "(NULL)", impsz);
if (dstr != NULL) {
free(dstr);
}
}
} else {
cli_dbgmsg("Imphash: failed to generate hash for import table (%d)\n", ret);
@ -5901,8 +5863,7 @@ int cli_genhash_pe(cli_ctx *ctx, unsigned int class, int type)
cli_dbgmsg("cli_genhash_pe: unknown pe genhash class: %u\n", class);
}
if (hash)
free(hash);
free(hash);
cli_exe_info_destroy(peinfo);
return CL_SUCCESS;
}

4
libclamav/pe.h
View file

@ -98,8 +98,8 @@ enum {
int cli_pe_targetinfo(fmap_t *map, struct cli_exe_info *peinfo);
int cli_peheader(fmap_t *map, struct cli_exe_info *peinfo, uint32_t opts, cli_ctx *ctx);
cl_error_t cli_checkfp_pe(cli_ctx *ctx, stats_section_t *hashes, uint32_t flags);
int cli_genhash_pe(cli_ctx *ctx, unsigned int class, int type);
cl_error_t cli_checkfp_pe(cli_ctx *ctx);
int cli_genhash_pe(cli_ctx *ctx, unsigned int class, int type, stats_section_t *hashes);
uint32_t cli_rawaddr(uint32_t, const struct cli_exe_section *, uint16_t, unsigned int *, size_t, uint32_t);
void findres(uint32_t, uint32_t, fmap_t *map, struct cli_exe_info *, int (*)(void *, uint32_t, uint32_t, uint32_t, uint32_t), void *);

9
sigtool/sigtool.c
View file

@ -255,10 +255,10 @@ static int hashpe(const char *filename, unsigned int class, int type)
/* Send to PE-specific hasher */
switch (class) {
case 1:
ret = cli_genhash_pe(&ctx, CL_GENHASH_PE_CLASS_SECTION, type);
ret = cli_genhash_pe(&ctx, CL_GENHASH_PE_CLASS_SECTION, type, NULL);
break;
case 2:
ret = cli_genhash_pe(&ctx, CL_GENHASH_PE_CLASS_IMPTBL, type);
ret = cli_genhash_pe(&ctx, CL_GENHASH_PE_CLASS_IMPTBL, type, NULL);
break;
default:
mprintf("!hashpe: unknown classification(%u) for pe hash!\n", class);
@ -3455,7 +3455,7 @@ static int dumpcerts(const struct optstruct *opts)
return -1;
}
ret = cli_checkfp_pe(&ctx, NULL, CL_CHECKFP_PE_FLAG_AUTHENTICODE);
ret = cli_checkfp_pe(&ctx);
switch (ret) {
case CL_CLEAN:
@ -3467,6 +3467,9 @@ static int dumpcerts(const struct optstruct *opts)
case CL_BREAK:
mprintf("*dumpcerts: CL_BREAK after cli_checkfp_pe()!\n");
break;
case CL_EVERIFY:
mprintf("!dumpcerts: CL_EVERIFY after cli_checkfp_pe()!\n");
break;
case CL_EFORMAT:
mprintf("!dumpcerts: An error occurred when parsing the file\n");
break;