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certs: Make blacklist_vet_description() more strict

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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: Mickaël Salaün <mic@linux.microsoft.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lore.kernel.org/r/20210712170313.884724-4-mic@digikod.net
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
This commit is contained in:
Mickaël Salaün 2021-07-12 19:03:11 +02:00 committed by Jarkko Sakkinen
parent 141e523914
commit bf21dc591b
1 changed files with 35 additions and 9 deletions
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44
certs/blacklist.c
View File

@ -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;
int i, prefix_len, tbs_step = 0, bin_step = 0;
if (*desc == ':')
return -EINVAL;
for (; *desc; desc++)
if (*desc == ':')
goto found_colon;
/* 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;
}