diff mbox series

[v1,2/9] certs: Make blacklist_vet_description() more strict

Message ID 20201120180426.922572-3-mic@digikod.net (mailing list archive)
State New
Headers show
Series Enable root to update the blacklist keyring | expand

Commit Message

Mickaël Salaün Nov. 20, 2020, 6:04 p.m. UTC 
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>
---
 certs/blacklist.c | 46 ++++++++++++++++++++++++++++++++++++----------
 1 file changed, 36 insertions(+), 10 deletions(-)

Comments

David Howells Dec. 4, 2020, 2:09 p.m. UTC | #1 
Mickaël Salaün <mic@digikod.net> wrote:

> +	if (*desc)
> +		/* The hash is greater than MAX_HASH_LEN. */
> +		return -EINVAL;

-ENOPKG might be better.  It's not that the string is invalid, it's just that
it's unsupported at the moment.

David
Mickaël Salaün Dec. 4, 2020, 2:59 p.m. UTC | #2 
On 04/12/2020 15:09, David Howells wrote:
> Mickaël Salaün <mic@digikod.net> wrote:
> 
>> +	if (*desc)
>> +		/* The hash is greater than MAX_HASH_LEN. */
>> +		return -EINVAL;
> 
> -ENOPKG might be better.  It's not that the string is invalid, it's just that
> it's unsupported at the moment.

Right, I'll switch to this with the next series.

> 
> David
>
Mickaël Salaün Dec. 11, 2020, 6:35 p.m. UTC | #3 
On 04/12/2020 15:09, David Howells wrote:
> Mickaël Salaün <mic@digikod.net> wrote:
> 
>> +	if (*desc)
>> +		/* The hash is greater than MAX_HASH_LEN. */
>> +		return -EINVAL;
> 
> -ENOPKG might be better.  It's not that the string is invalid, it's just that
> it's unsupported at the moment.

Indeed, I'll use that.

> 
> David
>
diff mbox series

Patch

diff --git a/certs/blacklist.c b/certs/blacklist.c
index 4e1a58170d5c..961359885881 100644
--- a/certs/blacklist.c
+++ b/certs/blacklist.c
@@ -17,6 +17,16 @@ 
 #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;
 
 /*
@@ -25,24 +35,40 @@  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 lenghts 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 -EINVAL;
 
-	if (n == 0 || n & 1)
+	/* Checks for an even number of hexadecimal characters. */
+	if (i == 0 || i & 1)
 		return -EINVAL;
 	return 0;
 }