[PATCH 27/27] KEYS: Restrict signature verification to keys appropriate to the purpose

@@ -536,7 +536,9 @@ static int bzImage64_verify_sig(const char *kernel, unsigned long kernel_len)
 	int ret;
 
 	ret = verify_pefile_signature(kernel, kernel_len,
-				      system_trusted_keyring, &trusted);
+				      system_trusted_keyring,
+				      KEY_VERIFYING_KEXEC_SIGNATURE,
+				      &trusted);
 	if (ret < 0)
 		return ret;
 	if (!trusted)

@@ -12,6 +12,7 @@
  */
 #include <keys/asymmetric-subtype.h>
 #include <keys/asymmetric-parser.h>
+#include <crypto/public_key.h>
 #include <linux/seq_file.h>
 #include <linux/module.h>
 #include <linux/slab.h>

@@ -20,6 +21,16 @@
 
 MODULE_LICENSE("GPL");
 
+const char *const key_being_used_for[NR__KEY_BEING_USED_FOR] = {
+	[KEY_VERIFYING_MODULE_SIGNATURE]	= "mod sig",
+	[KEY_VERIFYING_FIRMWARE_SIGNATURE]	= "firmware sig",
+	[KEY_VERIFYING_KEXEC_SIGNATURE]		= "kexec sig",
+	[KEY_VERIFYING_KEY_SIGNATURE]		= "key sig",
+	[KEY_VERIFYING_KEY_SELF_SIGNATURE]	= "key self sig",
+	[KEY_VERIFYING_INTEGRITY_SIGNATURE]	= "ima sig",
+};
+EXPORT_SYMBOL_GPL(key_being_used_for);
+
 static LIST_HEAD(asymmetric_key_parsers);
 static DECLARE_RWSEM(asymmetric_key_parsers_sem);
 

@@ -14,16 +14,23 @@
 #include <linux/err.h>
 #include <linux/module.h>
 #include <linux/key-type.h>
+#include <keys/asymmetric-type.h>
 #include <crypto/pkcs7.h>
 #include <keys/user-type.h>
 #include <keys/system_keyring.h>
 #include "pkcs7_parser.h"
 
+static unsigned pkcs7_usage;
+module_param_named(usage, pkcs7_usage, uint, S_IWUSR | S_IRUGO);
+MODULE_PARM_DESC(pkcs7_usage,
+		 "Usage to specify when verifying the PKCS#7 message");
+
 /*
  * Preparse a PKCS#7 wrapped and validated data blob.
  */
 static int pkcs7_preparse(struct key_preparsed_payload *prep)
 {
+	enum key_being_used_for usage = pkcs7_usage;
 	struct pkcs7_message *pkcs7;
 	const void *data, *saved_prep_data;
 	size_t datalen, saved_prep_datalen;

@@ -32,6 +39,11 @@ static int pkcs7_preparse(struct key_preparsed_payload *prep)
 
 	kenter("");
 
+	if (usage >= NR__KEY_BEING_USED_FOR) {
+		pr_err("Invalid usage type %d\n", usage);
+		return -EINVAL;
+	}
+
 	saved_prep_data = prep->data;
 	saved_prep_datalen = prep->datalen;
 	pkcs7 = pkcs7_parse_message(saved_prep_data, saved_prep_datalen);

@@ -40,11 +52,12 @@ static int pkcs7_preparse(struct key_preparsed_payload *prep)
 		goto error;
 	}
 
-	ret = pkcs7_verify(pkcs7);
+	ret = pkcs7_verify(pkcs7, usage);
 	if (ret < 0)
 		goto error_free;
 
-	ret = pkcs7_validate_trust(pkcs7, system_trusted_keyring, &trusted);
+	ret = pkcs7_validate_trust(pkcs7, system_trusted_keyring, usage,
+				   &trusted);
 	if (ret < 0)
 		goto error_free;
 	if (!trusted)

@@ -25,7 +25,8 @@
  */
 static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
 				    struct pkcs7_signed_info *sinfo,
-				    struct key *trust_keyring)
+				    struct key *trust_keyring,
+				    enum key_being_used_for usage)
 {
 	struct public_key_signature *sig = &sinfo->sig;
 	struct x509_certificate *x509, *last = NULL, *p;

@@ -65,6 +66,7 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
 			 */
 			pr_devel("sinfo %u: Cert %u as key %x\n",
 				 sinfo->index, x509->index, key_serial(key));
+			usage = KEY_VERIFYING_KEY_SIGNATURE;
 			goto matched;
 		}
 		if (key == ERR_PTR(-ENOMEM))

@@ -95,6 +97,7 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
 			x509 = last;
 			pr_devel("sinfo %u: Root cert %u signer is key %x\n",
 				 sinfo->index, x509->index, key_serial(key));
+			usage = KEY_VERIFYING_KEY_SIGNATURE;
 			goto matched;
 		}
 		if (PTR_ERR(key) != -ENOKEY)

@@ -121,7 +124,7 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
 	return -ENOKEY;
 
 matched:
-	ret = verify_signature(key, sig);
+	ret = verify_signature(key, sig, usage);
 	trusted = test_bit(KEY_FLAG_TRUSTED, &key->flags);
 	key_put(key);
 	if (ret < 0) {

@@ -148,7 +151,8 @@ verified:
  * pkcs7_validate_trust - Validate PKCS#7 trust chain
  * @pkcs7: The PKCS#7 certificate to validate
  * @trust_keyring: Signing certificates to use as starting points
- * @_trusted: Set to true if trustworth, false otherwise
+ * @usage: The use to which the key is being put.
+ * @_trusted: Set to true if trustworthy, false otherwise
  *
  * Validate that the certificate chain inside the PKCS#7 message intersects
  * keys we already know and trust.

@@ -171,6 +175,7 @@ verified:
  */
 int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
 			 struct key *trust_keyring,
+			 enum key_being_used_for usage,
 			 bool *_trusted)
 {
 	struct pkcs7_signed_info *sinfo;

@@ -182,7 +187,8 @@ int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
 		p->seen = false;
 
 	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
-		ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring);
+		ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring,
+					       usage);
 		switch (ret) {
 		case -ENOKEY:
 			continue;

@@ -208,7 +208,8 @@ static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 				   x509->raw_issuer_size) != 0)
 				return 0;
 
-			ret = x509_check_signature(x509->pub, x509);
+			ret = x509_check_signature(x509->pub, x509,
+						   KEY_VERIFYING_KEY_SELF_SIGNATURE);
 			if (ret < 0)
 				goto maybe_missing_crypto_in_x509;
 			x509->signer = x509;

@@ -262,7 +263,8 @@ static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 				sinfo->index);
 			return 0;
 		}
-		ret = x509_check_signature(p->pub, x509);
+		ret = x509_check_signature(p->pub, x509,
+					   KEY_VERIFYING_KEY_SIGNATURE);
 		if (ret < 0)
 			return ret;
 		x509->signer = p;

@@ -290,7 +292,8 @@ maybe_missing_crypto_in_x509:
  * Verify one signed information block from a PKCS#7 message.
  */
 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
-			    struct pkcs7_signed_info *sinfo)
+			    struct pkcs7_signed_info *sinfo,
+			    enum key_being_used_for usage)
 {
 	int ret;
 

@@ -315,7 +318,8 @@ static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
 		 sinfo->signer->index, sinfo->index);
 
 	/* Verify the PKCS#7 binary against the key */
-	ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig);
+	ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig,
+					  usage);
 	if (ret < 0)
 		return ret;
 

@@ -328,6 +332,7 @@ static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
 /**
  * pkcs7_verify - Verify a PKCS#7 message
  * @pkcs7: The PKCS#7 message to be verified
+ * @usage: The use to which the key is being put
  *
  * Verify a PKCS#7 message is internally consistent - that is, the data digest
  * matches the digest in the AuthAttrs and any signature in the message or one

@@ -339,6 +344,9 @@ static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
  *
  * Returns, in order of descending priority:
  *
+ *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
+ *      odds with the specified usage, or:
+ *
  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
  *	appropriate X.509 certificate, or:
  *

@@ -350,7 +358,8 @@ static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
  *  (*) 0 if all the signature chains that don't incur -ENOPKG can be verified
  *	(note that a signature chain may be of zero length), or:
  */
-int pkcs7_verify(struct pkcs7_message *pkcs7)
+int pkcs7_verify(struct pkcs7_message *pkcs7,
+		 enum key_being_used_for usage)
 {
 	struct pkcs7_signed_info *sinfo;
 	struct x509_certificate *x509;

@@ -366,7 +375,7 @@ int pkcs7_verify(struct pkcs7_message *pkcs7)
 	}
 
 	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
-		ret = pkcs7_verify_one(pkcs7, sinfo);
+		ret = pkcs7_verify_one(pkcs7, sinfo, usage);
 		if (ret < 0) {
 			if (ret == -ENOPKG) {
 				sinfo->unsupported_crypto = true;

@@ -39,6 +39,7 @@ EXPORT_SYMBOL_GPL(pkey_algo);
 const char *const pkey_id_type_name[PKEY_ID_TYPE__LAST] = {
 	[PKEY_ID_PGP]		= "PGP",
 	[PKEY_ID_X509]		= "X509",
+	[PKEY_ID_PKCS7]		= "PKCS#7",
 };
 EXPORT_SYMBOL_GPL(pkey_id_type_name);
 

@@ -94,12 +95,56 @@ void public_key_destroy(void *payload)
 EXPORT_SYMBOL_GPL(public_key_destroy);
 
 /*
+ * Apply key usage policy.
+ */
+static int public_key_usage_policy(enum key_being_used_for usage,
+				   enum key_usage_restriction restriction)
+{
+	switch (usage) {
+	case KEY_VERIFYING_MODULE_SIGNATURE:
+		if (restriction != KEY_RESTRICTED_TO_MODULE_SIGNING &&
+		    restriction != KEY_USAGE_NOT_SPECIFIED)
+			goto wrong_purpose;
+		return 0;
+	case KEY_VERIFYING_FIRMWARE_SIGNATURE:
+		if (restriction != KEY_RESTRICTED_TO_FIRMWARE_SIGNING) {
+			pr_warn("Firmware signed with non-firmware key (%s)\n",
+				key_usage_restrictions[restriction]);
+			return -EKEYREJECTED;
+		}
+		return 0;
+	case KEY_VERIFYING_KEXEC_SIGNATURE:
+		if (restriction != KEY_RESTRICTED_TO_KEXEC_SIGNING &&
+		    restriction != KEY_USAGE_NOT_SPECIFIED)
+			goto wrong_purpose;
+		return 0;
+	case KEY_VERIFYING_KEY_SIGNATURE:
+		if (restriction != KEY_RESTRICTED_TO_KEY_SIGNING &&
+		    restriction != KEY_USAGE_NOT_SPECIFIED)
+			goto wrong_purpose;
+		return 0;
+	case KEY_VERIFYING_KEY_SELF_SIGNATURE:
+		return 0;
+	default:
+		BUG();
+	}
+
+wrong_purpose:
+	pr_warn("Restricted usage key (%s) used for wrong purpose (%s)\n",
+		key_usage_restrictions[restriction],
+		key_being_used_for[usage]);
+	return -EKEYREJECTED;
+}
+
+/*
  * Verify a signature using a public key.
  */
 int public_key_verify_signature(const struct public_key *pk,
-				const struct public_key_signature *sig)
+				const struct public_key_signature *sig,
+				enum key_being_used_for usage)
 {
 	const struct public_key_algorithm *algo;
+	int ret;
 
 	BUG_ON(!pk);
 	BUG_ON(!pk->mpi[0]);

@@ -126,15 +171,20 @@ int public_key_verify_signature(const struct public_key *pk,
 		return -EINVAL;
 	}
 
+	ret = public_key_usage_policy(usage, pk->usage_restriction);
+	if (ret < 0)
+		return ret;
+
 	return algo->verify_signature(pk, sig);
 }
 EXPORT_SYMBOL_GPL(public_key_verify_signature);
 
 static int public_key_verify_signature_2(const struct key *key,
-					 const struct public_key_signature *sig)
+					 const struct public_key_signature *sig,
+					 enum key_being_used_for usage)
 {
 	const struct public_key *pk = key->payload.data;
-	return public_key_verify_signature(pk, sig);
+	return public_key_verify_signature(pk, sig, usage);
 }
 
 /*

@@ -33,4 +33,5 @@ extern const struct public_key_algorithm RSA_public_key_algorithm;
  * public_key.c
  */
 extern int public_key_verify_signature(const struct public_key *pk,
-				       const struct public_key_signature *sig);
+				       const struct public_key_signature *sig,
+				       enum key_being_used_for usage);

@@ -22,11 +22,13 @@
  * verify_signature - Initiate the use of an asymmetric key to verify a signature
  * @key: The asymmetric key to verify against
  * @sig: The signature to check
+ * @usage: The use to which the key is being put.
  *
  * Returns 0 if successful or else an error.
  */
 int verify_signature(const struct key *key,
-		     const struct public_key_signature *sig)
+		     const struct public_key_signature *sig,
+		     enum key_being_used_for usage)
 {
 	const struct asymmetric_key_subtype *subtype;
 	int ret;

@@ -42,7 +44,7 @@ int verify_signature(const struct key *key,
 	if (!subtype->verify_signature)
 		return -ENOTSUPP;
 
-	ret = subtype->verify_signature(key, sig);
+	ret = subtype->verify_signature(key, sig, usage);
 
 	pr_devel("<==%s() = %d\n", __func__, ret);
 	return ret;

@@ -393,6 +393,7 @@ error_no_desc:
  * @pebuf: Buffer containing the PE binary image
  * @pelen: Length of the binary image
  * @trust_keyring: Signing certificates to use as starting points
+ * @usage: The use to which the key is being put.
  * @_trusted: Set to true if trustworth, false otherwise
  *
  * Validate that the certificate chain inside the PKCS#7 message inside the PE

@@ -417,7 +418,9 @@ error_no_desc:
  * May also return -ENOMEM.
  */
 int verify_pefile_signature(const void *pebuf, unsigned pelen,
-			    struct key *trusted_keyring, bool *_trusted)
+			    struct key *trusted_keyring,
+			    enum key_being_used_for usage,
+			    bool *_trusted)
 {
 	struct pkcs7_message *pkcs7;
 	struct pefile_context ctx;

@@ -462,11 +465,11 @@ int verify_pefile_signature(const void *pebuf, unsigned pelen,
 	if (ret < 0)
 		goto error;
 
-	ret = pkcs7_verify(pkcs7);
+	ret = pkcs7_verify(pkcs7, usage);
 	if (ret < 0)
 		goto error;
 
-	ret = pkcs7_validate_trust(pkcs7, trusted_keyring, _trusted);
+	ret = pkcs7_validate_trust(pkcs7, trusted_keyring, usage, _trusted);
 
 error:
 	pkcs7_free_message(ctx.pkcs7);

@@ -55,4 +55,5 @@ extern struct x509_certificate *x509_cert_parse(const void *data, size_t datalen
  */
 extern int x509_get_sig_params(struct x509_certificate *cert);
 extern int x509_check_signature(const struct public_key *pub,
-				struct x509_certificate *cert);
+				struct x509_certificate *cert,
+				enum key_being_used_for usage);

@@ -221,7 +221,8 @@ EXPORT_SYMBOL_GPL(x509_get_sig_params);
  * Check the signature on a certificate using the provided public key
  */
 int x509_check_signature(const struct public_key *pub,
-			 struct x509_certificate *cert)
+			 struct x509_certificate *cert,
+			 enum key_being_used_for usage)
 {
 	int ret;
 

@@ -231,7 +232,7 @@ int x509_check_signature(const struct public_key *pub,
 	if (ret < 0)
 		return ret;
 
-	ret = public_key_verify_signature(pub, &cert->sig);
+	ret = public_key_verify_signature(pub, &cert->sig, usage);
 	if (ret == -ENOPKG)
 		cert->unsupported_crypto = true;
 	pr_debug("Cert Verification: %d\n", ret);

@@ -264,9 +265,10 @@ static int x509_validate_trust(struct x509_certificate *cert,
 					  cert->akid_id, cert->akid_skid,
 					  false);
 	if (!IS_ERR(key))  {
-		if (!use_builtin_keys
-		    || test_bit(KEY_FLAG_BUILTIN, &key->flags))
-			ret = x509_check_signature(key->payload.data, cert);
+		if (!use_builtin_keys ||
+		    test_bit(KEY_FLAG_BUILTIN, &key->flags))
+			ret = x509_check_signature(key->payload.data, cert,
+						   KEY_VERIFYING_KEY_SIGNATURE);
 		key_put(key);
 	}
 	return ret;

@@ -321,7 +323,8 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
 	if ((!cert->akid_skid && !cert->akid_id) ||
 	    asymmetric_key_id_same(cert->skid, cert->akid_skid) ||
 	    asymmetric_key_id_same(cert->id, cert->akid_id)) {
-		ret = x509_check_signature(cert->pub, cert); /* self-signed */
+		ret = x509_check_signature(cert->pub, cert,
+					   KEY_VERIFYING_KEY_SELF_SIGNATURE);
 		if (ret < 0)
 			goto error_free_cert;
 	} else if (!prep->trusted) {

@@ -9,6 +9,8 @@
  * 2 of the Licence, or (at your option) any later version.
  */
 
+#include <crypto/public_key.h>
+
 struct key;
 struct pkcs7_message;
 

@@ -29,12 +31,14 @@ extern const char *pkcs7_get_firmware_name(const struct pkcs7_message *pkcs7);
  */
 extern int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
 				struct key *trust_keyring,
+				enum key_being_used_for usage,
 				bool *_trusted);
 
 /*
  * pkcs7_verify.c
  */
-extern int pkcs7_verify(struct pkcs7_message *pkcs7);
+extern int pkcs7_verify(struct pkcs7_message *pkcs7,
+			enum key_being_used_for usage);
 
 extern int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
 				      const void *data, size_t datalen);

@@ -53,6 +53,19 @@ enum key_usage_restriction {
 	NR__KEY_USAGE_RESTRICTIONS
 };
 
+/*
+ * The use to which an asymmetric key is being put when verifying a signature.
+ */
+enum key_being_used_for {
+	KEY_VERIFYING_MODULE_SIGNATURE,
+	KEY_VERIFYING_FIRMWARE_SIGNATURE,
+	KEY_VERIFYING_KEXEC_SIGNATURE,
+	KEY_VERIFYING_KEY_SIGNATURE,
+	KEY_VERIFYING_KEY_SELF_SIGNATURE,
+	KEY_VERIFYING_INTEGRITY_SIGNATURE,
+	NR__KEY_BEING_USED_FOR
+};
+extern const char *const key_being_used_for[NR__KEY_BEING_USED_FOR];
 
 /*
  * Cryptographic data for the public-key subtype of the asymmetric key type.

@@ -114,7 +127,8 @@ struct public_key_signature {
 
 struct key;
 extern int verify_signature(const struct key *key,
-			    const struct public_key_signature *sig);
+			    const struct public_key_signature *sig,
+			    enum key_being_used_for usage);
 
 struct asymmetric_key_id;
 extern struct key *x509_request_asymmetric_key(struct key *keyring,

@@ -18,6 +18,7 @@
 #include <keys/asymmetric-type.h>
 
 struct public_key_signature;
+enum key_being_used_for;
 
 /*
  * Keys of this type declare a subtype that indicates the handlers and

@@ -39,7 +40,8 @@ struct asymmetric_key_subtype {
 
 	/* Verify the signature on a key of this subtype (optional) */
 	int (*verify_signature)(const struct key *key,
-				const struct public_key_signature *sig);
+				const struct public_key_signature *sig,
+				enum key_being_used_for usage);
 };
 
 /**

@@ -15,6 +15,7 @@
 #ifdef CONFIG_SYSTEM_TRUSTED_KEYRING
 
 #include <linux/key.h>
+#include <crypto/public_key.h>
 
 extern struct key *system_trusted_keyring;
 static inline struct key *get_system_trusted_keyring(void)

@@ -31,6 +32,7 @@ static inline struct key *get_system_trusted_keyring(void)
 #ifdef CONFIG_SYSTEM_DATA_VERIFICATION
 extern int system_verify_data(const void *data, unsigned long len,
 			      const void *raw_pkcs7, size_t pkcs7_len,
+			      enum key_being_used_for usage,
 			      const char *firmware_name);
 #endif
 

@@ -12,7 +12,11 @@
 #ifndef _LINUX_VERIFY_PEFILE_H
 #define _LINUX_VERIFY_PEFILE_H
 
+#include <crypto/public_key.h>
+
 extern int verify_pefile_signature(const void *pebuf, unsigned pelen,
-				   struct key *trusted_keyring, bool *_trusted);
+				   struct key *trusted_keyring,
+				   enum key_being_used_for usage,
+				   bool *_trusted);
 
 #endif /* _LINUX_VERIFY_PEFILE_H */

@@ -72,5 +72,6 @@ int mod_verify_sig(const void *mod, unsigned long *_modlen)
 		return -EBADMSG;
 	}
 
-	return system_verify_data(mod, modlen, mod + modlen, sig_len, NULL);
+	return system_verify_data(mod, modlen, mod + modlen, sig_len,
+				  KEY_VERIFYING_MODULE_SIGNATURE, NULL);
 }

@@ -113,10 +113,12 @@ late_initcall(load_system_certificate_list);
  * @len: Size of @data.
  * @raw_pkcs7: The PKCS#7 message that is the signature.
  * @pkcs7_len: The size of @raw_pkcs7.
+ * @usage: The use to which the key is being put.
  * @firmware_name: The required firmware name or NULL.
  */
 int system_verify_data(const void *data, unsigned long len,
 		       const void *raw_pkcs7, size_t pkcs7_len,
+		       enum key_being_used_for usage,
 		       const char *firmware_name)
 {
 	struct pkcs7_message *pkcs7;

@@ -156,11 +158,12 @@ int system_verify_data(const void *data, unsigned long len,
 		goto error;
 	}
 
-	ret = pkcs7_verify(pkcs7);
+	ret = pkcs7_verify(pkcs7, usage);
 	if (ret < 0)
 		goto error;
 
-	ret = pkcs7_validate_trust(pkcs7, system_trusted_keyring, &trusted);
+	ret = pkcs7_validate_trust(pkcs7, system_trusted_keyring, usage,
+				   &trusted);
 	if (ret < 0)
 		goto error;
 

@@ -96,7 +96,8 @@ int asymmetric_verify(struct key *keyring, const char *sig,
 	pks.rsa.s = mpi_read_raw_data(hdr->sig, siglen);
 
 	if (pks.rsa.s)
-		ret = verify_signature(key, &pks);
+		ret = verify_signature(key, &pks,
+				       KEY_VERIFYING_INTEGRITY_SIGNATURE);
 
 	mpi_free(pks.rsa.s);
 	key_put(key);