Commit bf21dc59 authored by Mickaël Salaün's avatar Mickaël Salaün Committed by Jarkko Sakkinen
Browse files

certs: Make blacklist_vet_description() more strict 



Before exposing this new key type to user space, make sure that only
meaningful blacklisted hashes are accepted.  This is also checked for
builtin blacklisted hashes, but a following commit make sure that the
user will notice (at built time) and will fix the configuration if it
already included errors.

Check that a blacklist key description starts with a valid prefix and
then a valid hexadecimal string.

Cc: David Howells <dhowells@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Eric Snowberg <eric.snowberg@oracle.com>
Signed-off-by: default avatarMickaël Salaün <mic@linux.microsoft.com>
Reviewed-by: default avatarJarkko Sakkinen <jarkko@kernel.org>
Link: https://lore.kernel.org/r/20210712170313.884724-4-mic@digikod.net


Signed-off-by: default avatarJarkko Sakkinen <jarkko@kernel.org>
parent 141e5239

certs/blacklist.c

+36 −10
Original line number Diff line number Diff line
@@ -19,6 +19,16 @@ 
#include "blacklist.h"

#include "common.h"



/*

 * According to crypto/asymmetric_keys/x509_cert_parser.c:x509_note_pkey_algo(),

 * the size of the currently longest supported hash algorithm is 512 bits,

 * which translates into 128 hex characters.

 */

#define MAX_HASH_LEN	128



static const char tbs_prefix[] = "tbs";

static const char bin_prefix[] = "bin";



static struct key *blacklist_keyring;



#ifdef CONFIG_SYSTEM_REVOCATION_LIST
@@ -32,24 +42,40 @@ extern __initconst const unsigned long revocation_certificate_list_size; 
 */

static int blacklist_vet_description(const char *desc)

{

	int n = 0;



	if (*desc == ':')

		return -EINVAL;

	for (; *desc; desc++)

		if (*desc == ':')

	int i, prefix_len, tbs_step = 0, bin_step = 0;



	/* The following algorithm only works if prefix lengths match. */

	BUILD_BUG_ON(sizeof(tbs_prefix) != sizeof(bin_prefix));

	prefix_len = sizeof(tbs_prefix) - 1;

	for (i = 0; *desc; desc++, i++) {

		if (*desc == ':') {

			if (tbs_step == prefix_len)

				goto found_colon;

			if (bin_step == prefix_len)

				goto found_colon;

			return -EINVAL;

		}

		if (i >= prefix_len)

			return -EINVAL;

		if (*desc == tbs_prefix[i])

			tbs_step++;

		if (*desc == bin_prefix[i])

			bin_step++;

	}

	return -EINVAL;



found_colon:

	desc++;

	for (; *desc; desc++) {

	for (i = 0; *desc && i < MAX_HASH_LEN; desc++, i++) {

		if (!isxdigit(*desc) || isupper(*desc))

			return -EINVAL;

		n++;

	}

	if (*desc)

		/* The hash is greater than MAX_HASH_LEN. */

		return -ENOPKG;



	if (n == 0 || n & 1)

	/* Checks for an even number of hexadecimal characters. */

	if (i == 0 || i & 1)

		return -EINVAL;

	return 0;

}