From: "Mickaël Salaün" <mic@digikod.net>
To: David Howells <dhowells@redhat.com>,
David Woodhouse <dwmw2@infradead.org>,
Jarkko Sakkinen <jarkko@kernel.org>
Cc: "Mickaël Salaün" <mic@digikod.net>,
"David S . Miller" <davem@davemloft.net>,
"Herbert Xu" <herbert@gondor.apana.org.au>,
"James Morris" <jmorris@namei.org>,
"Mickaël Salaün" <mic@linux.microsoft.com>,
"Mimi Zohar" <zohar@linux.ibm.com>,
"Serge E . Hallyn" <serge@hallyn.com>,
"Tyler Hicks" <tyhicks@linux.microsoft.com>,
keyrings@vger.kernel.org, linux-crypto@vger.kernel.org,
linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-security-module@vger.kernel.org
Subject: [PATCH v4 06/10] certs: Make blacklist_vet_description() more strict
Date: Thu, 21 Jan 2021 16:55:09 +0100 [thread overview]
Message-ID: <20210121155513.539519-7-mic@digikod.net> (raw)
In-Reply-To: <20210121155513.539519-1-mic@digikod.net>
From: Mickaël Salaün <mic@linux.microsoft.com>
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>
Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
---
Changes since v2:
* Fix typo in blacklist_vet_description() comment, spotted by Tyler
Hicks.
* Add Jarkko's Acked-by.
Changes since v1:
* Return ENOPKG (instead of EINVAL) when a hash is greater than the
maximum currently known hash (suggested by David Howells).
---
certs/blacklist.c | 46 ++++++++++++++++++++++++++++++++++++----------
1 file changed, 36 insertions(+), 10 deletions(-)
diff --git a/certs/blacklist.c b/certs/blacklist.c
index 8a64b9e89cae..069050884bd2 100644
--- a/certs/blacklist.c
+++ b/certs/blacklist.c
@@ -18,6 +18,16 @@
#include <keys/system_keyring.h>
#include "blacklist.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;
/*
@@ -26,24 +36,40 @@ static struct key *blacklist_keyring;
*/
static int blacklist_vet_description(const char *desc)
{
- int n = 0;
-
- if (*desc == ':')
- return -EINVAL;
- for (; *desc; desc++)
- if (*desc == ':')
- goto found_colon;
+ 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;
}
--
2.30.0
next prev parent reply other threads:[~2021-01-21 16:51 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-21 15:55 [PATCH v4 00/10] Enable root to update the blacklist keyring Mickaël Salaün
2021-01-21 15:55 ` [PATCH v4 01/10] tools/certs: Add print-cert-tbs-hash.sh Mickaël Salaün
2021-01-21 15:55 ` [PATCH v4 02/10] certs: Check that builtin blacklist hashes are valid Mickaël Salaün
2021-01-21 15:55 ` [PATCH v4 03/10] certs: Fix blacklisted hexadecimal hash string check Mickaël Salaün
2021-01-21 15:55 ` [PATCH v4 04/10] certs: Fix blacklist flag type confusion Mickaël Salaün
2021-01-21 15:55 ` [PATCH v4 05/10] certs: Replace K{U,G}IDT_INIT() with GLOBAL_ROOT_{U,G}ID Mickaël Salaün
2021-01-21 15:55 ` Mickaël Salaün [this message]
2021-01-21 15:55 ` [PATCH v4 07/10] certs/blacklist: fix kernel doc interface issue Mickaël Salaün
2021-01-21 15:55 ` [PATCH v4 08/10] certs: Factor out the blacklist hash creation Mickaël Salaün
2021-01-21 15:55 ` [PATCH v4 09/10] PKCS#7: Fix missing include Mickaël Salaün
2021-01-21 15:55 ` [PATCH v4 10/10] certs: Allow root user to append signed hashes to the blacklist keyring Mickaël Salaün
2021-01-28 16:52 ` [PATCH v4 00/10] Enable root to update " David Howells
2021-01-28 17:38 ` Mickaël Salaün
2021-01-28 18:00 ` Mickaël Salaün
2021-01-30 19:39 ` Jarkko Sakkinen
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