KEYS: verify a certificate is signed by a 'trusted' key

Only public keys, with certificates signed by an existing 'trusted' key on the system trusted keyring, should be added to a trusted keyring. This patch adds support for verifying a certificate's signature. This is derived from David Howells pkcs7_request_asymmetric_key() patch. Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com> Signed-off-by: David Howells <dhowells@redhat.com>

KEYS: verify a certificate is signed by a 'trusted' key
Only public keys, with certificates signed by an existing 'trusted' key on the system trusted keyring, should be added to a trusted keyring. This patch adds support for verifying a certificate's signature. This is derived from David Howells pkcs7_request_asymmetric_key() patch. Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com> Signed-off-by: David Howells <dhowells@redhat.com>
Mimi Zohar · David Howells
1 parent af34cb0c3d
Showing 1 changed file with 80 additions and 1 deletions Side-by-side Diff
crypto/asymmetric_keys/x509_public_key.c
@@ -18,12 +18,60 @@
 #include <linux/asn1_decoder.h>
 #include <keys/asymmetric-subtype.h>
 #include <keys/asymmetric-parser.h>
+#include <keys/system_keyring.h>
 #include <crypto/hash.h>
 #include "asymmetric_keys.h"
 #include "public_key.h"
 #include "x509_parser.h"
  
 /*
+ * Find a key in the given keyring by issuer and authority.
+ */
+static struct key *x509_request_asymmetric_key(
+	struct key *keyring,
+	const char *signer, size_t signer_len,
+	const char *authority, size_t auth_len)
+{
+	key_ref_t key;
+	char *id;
+
+	/* Construct an identifier. */
+	id = kmalloc(signer_len + 2 + auth_len + 1, GFP_KERNEL);
+	if (!id)
+		return ERR_PTR(-ENOMEM);
+
+	memcpy(id, signer, signer_len);
+	id[signer_len + 0] = ':';
+	id[signer_len + 1] = ' ';
+	memcpy(id + signer_len + 2, authority, auth_len);
+	id[signer_len + 2 + auth_len] = 0;
+
+	pr_debug("Look up: \"%s\"\n", id);
+
+	key = keyring_search(make_key_ref(keyring, 1),
+			     &key_type_asymmetric, id);
+	if (IS_ERR(key))
+		pr_debug("Request for module key '%s' err %ld\n",
+			 id, PTR_ERR(key));
+	kfree(id);
+
+	if (IS_ERR(key)) {
+		switch (PTR_ERR(key)) {
+			/* Hide some search errors */
+		case -EACCES:
+		case -ENOTDIR:
+		case -EAGAIN:
+			return ERR_PTR(-ENOKEY);
+		default:
+			return ERR_CAST(key);
+		}
+	}
+
+	pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key_ref_to_ptr(key)));
+	return key_ref_to_ptr(key);
+}
+
+/*
  * Set up the signature parameters in an X.509 certificate.  This involves
  * digesting the signed data and extracting the signature.
  */
@@ -103,6 +151,33 @@
 EXPORT_SYMBOL_GPL(x509_check_signature);
  
 /*
+ * Check the new certificate against the ones in the trust keyring.  If one of
+ * those is the signing key and validates the new certificate, then mark the
+ * new certificate as being trusted.
+ *
+ * Return 0 if the new certificate was successfully validated, 1 if we couldn't
+ * find a matching parent certificate in the trusted list and an error if there
+ * is a matching certificate but the signature check fails.
+ */
+static int x509_validate_trust(struct x509_certificate *cert,
+			       struct key *trust_keyring)
+{
+	const struct public_key *pk;
+	struct key *key;
+	int ret = 1;
+
+	key = x509_request_asymmetric_key(trust_keyring,
+					  cert->issuer, strlen(cert->issuer),
+					  cert->authority,
+					  strlen(cert->authority));
+	if (!IS_ERR(key))  {
+		pk = key->payload.data;
+		ret = x509_check_signature(pk, cert);
+	}
+	return ret;
+}
+
+/*
  * Attempt to parse a data blob for a key as an X509 certificate.
  */
 static int x509_key_preparse(struct key_preparsed_payload *prep)
  
@@ -155,9 +230,13 @@
 	/* Check the signature on the key if it appears to be self-signed */
 	if (!cert->authority ||
 	    strcmp(cert->fingerprint, cert->authority) == 0) {
-		ret = x509_check_signature(cert->pub, cert);
+		ret = x509_check_signature(cert->pub, cert); /* self-signed */
 		if (ret < 0)
 			goto error_free_cert;
+	} else {
+		ret = x509_validate_trust(cert, system_trusted_keyring);
+		if (!ret)
+			prep->trusted = 1;
 	}
  
 	/* Propose a description */
...	...	@@ -18,12 +18,60 @@
18	18	#include <linux/asn1_decoder.h>
19	19	#include <keys/asymmetric-subtype.h>
20	20	#include <keys/asymmetric-parser.h>
	21	+#include <keys/system_keyring.h>
21	22	#include <crypto/hash.h>
22	23	#include "asymmetric_keys.h"
23	24	#include "public_key.h"
24	25	#include "x509_parser.h"
25	26
26	27	/*
	28	+ * Find a key in the given keyring by issuer and authority.
	29	+ */
	30	+static struct key *x509_request_asymmetric_key(
	31	+ struct key *keyring,
	32	+ const char *signer, size_t signer_len,
	33	+ const char *authority, size_t auth_len)
	34	+{
	35	+ key_ref_t key;
	36	+ char *id;
	37	+
	38	+ /* Construct an identifier. */
	39	+ id = kmalloc(signer_len + 2 + auth_len + 1, GFP_KERNEL);
	40	+ if (!id)
	41	+ return ERR_PTR(-ENOMEM);
	42	+
	43	+ memcpy(id, signer, signer_len);
	44	+ id[signer_len + 0] = ':';
	45	+ id[signer_len + 1] = ' ';
	46	+ memcpy(id + signer_len + 2, authority, auth_len);
	47	+ id[signer_len + 2 + auth_len] = 0;
	48	+
	49	+ pr_debug("Look up: \"%s\"\n", id);
	50	+
	51	+ key = keyring_search(make_key_ref(keyring, 1),
	52	+ &key_type_asymmetric, id);
	53	+ if (IS_ERR(key))
	54	+ pr_debug("Request for module key '%s' err %ld\n",
	55	+ id, PTR_ERR(key));
	56	+ kfree(id);
	57	+
	58	+ if (IS_ERR(key)) {
	59	+ switch (PTR_ERR(key)) {
	60	+ /* Hide some search errors */
	61	+ case -EACCES:
	62	+ case -ENOTDIR:
	63	+ case -EAGAIN:
	64	+ return ERR_PTR(-ENOKEY);
	65	+ default:
	66	+ return ERR_CAST(key);
	67	+ }
	68	+ }
	69	+
	70	+ pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key_ref_to_ptr(key)));
	71	+ return key_ref_to_ptr(key);
	72	+}
	73	+
	74	+/*
27	75	* Set up the signature parameters in an X.509 certificate. This involves
28	76	* digesting the signed data and extracting the signature.
29	77	*/
...	...	@@ -103,6 +151,33 @@
103	151	EXPORT_SYMBOL_GPL(x509_check_signature);
104	152
105	153	/*
	154	+ * Check the new certificate against the ones in the trust keyring. If one of
	155	+ * those is the signing key and validates the new certificate, then mark the
	156	+ * new certificate as being trusted.
	157	+ *
	158	+ * Return 0 if the new certificate was successfully validated, 1 if we couldn't
	159	+ * find a matching parent certificate in the trusted list and an error if there
	160	+ * is a matching certificate but the signature check fails.
	161	+ */
	162	+static int x509_validate_trust(struct x509_certificate *cert,
	163	+ struct key *trust_keyring)
	164	+{
	165	+ const struct public_key *pk;
	166	+ struct key *key;
	167	+ int ret = 1;
	168	+
	169	+ key = x509_request_asymmetric_key(trust_keyring,
	170	+ cert->issuer, strlen(cert->issuer),
	171	+ cert->authority,
	172	+ strlen(cert->authority));
	173	+ if (!IS_ERR(key)) {
	174	+ pk = key->payload.data;
	175	+ ret = x509_check_signature(pk, cert);
	176	+ }
	177	+ return ret;
	178	+}
	179	+
	180	+/*
106	181	* Attempt to parse a data blob for a key as an X509 certificate.
107	182	*/
108	183	static int x509_key_preparse(struct key_preparsed_payload *prep)
109	184
...	...	@@ -155,9 +230,13 @@
155	230	/* Check the signature on the key if it appears to be self-signed */
156	231	if (!cert->authority \|\|
157	232	strcmp(cert->fingerprint, cert->authority) == 0) {
158		- ret = x509_check_signature(cert->pub, cert);
	233	+ ret = x509_check_signature(cert->pub, cert); /* self-signed */
159	234	if (ret < 0)
160	235	goto error_free_cert;
	236	+ } else {
	237	+ ret = x509_validate_trust(cert, system_trusted_keyring);
	238	+ if (!ret)
	239	+ prep->trusted = 1;
161	240	}
162	241
163	242	/* Propose a description */