[PATCH 27/27] PKCS#7: Restrict content type and authenticated attributes by purpose [ver #7]

[David Howells <dhowells@redhat.com>]

Restrict the content type in the and the authenticated attributes permitted
in a PKCS#7 SignedData object according the purpose to which the message is
being put:

 (*) VERIFYING_MODULE_SIGNATURE
 (*) VERIFYING_FIRMWARE_SIGNATURE
 (*) VERIFYING_UNSPECIFIED_SIGNATURE

     These three all require the SignedData content type to be pkcs7-data.
     The first also forbids authattrs, the second requires them and the
     third is okay either way.

 (*) VERIFYING_KEXEC_PE_SIGNATURE

     This only supports the Authenticode SPC_INDIRECT_DATA content type and
     requires at least an SpcSpOpusInfo authattr but also permits an
     SPC_STATEMENT_TYPE authattr (and an S/MIME capabilities authattr
     because the pesign program doesn't remove these).

 (*) VERIFYING_KEY_SIGNATURE
 (*) VERIFYING_KEY_SELF_SIGNATURE

     These are invalid in this context but are included for later use when
     limiting the use of X.509 certs.



The PKCS#7 test key type is given the usage to specify in a module
parameter.  For example:

	echo 1 >/sys/module/pkcs7_test_key/parameters/usage
	keyctl padd pkcs7_test foo @s </tmp/stuff.pkcs7

will attempt to check the signature on stuff.pkcs7 as if it contains a
firmware blob (1 being VERIFYING_FIRMWARE_SIGNATURE).

Signed-off-by: David Howells <dhowells@redhat.com>
---

 arch/x86/kernel/kexec-bzimage64.c        |    4 +++-
 crypto/asymmetric_keys/asymmetric_type.c |   11 ++++++++++
 crypto/asymmetric_keys/pkcs7_key_type.c  |   19 +++++++++++------
 crypto/asymmetric_keys/pkcs7_verify.c    |   34 ++++++++++++++++++++----------
 crypto/asymmetric_keys/verify_pefile.c   |    7 ++++--
 include/crypto/pkcs7.h                   |    9 +++-----
 include/crypto/public_key.h              |   14 ++++++++++++
 include/keys/system_keyring.h            |    4 +++-
 include/linux/verify_pefile.h            |    6 ++++-
 kernel/module_signing.c                  |    3 ++-
 kernel/system_keyring.c                  |    6 ++++-
 11 files changed, 85 insertions(+), 32 deletions(-)

diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
index ca83f7ac388b..fab22e72808c 100644
--- a/arch/x86/kernel/kexec-bzimage64.c
+++ b/arch/x86/kernel/kexec-bzimage64.c
@@ -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,
+				      VERIFYING_KEXEC_PE_SIGNATURE,
+				      &trusted);
 	if (ret < 0)
 		return ret;
 	if (!trusted)
diff --git a/crypto/asymmetric_keys/asymmetric_type.c b/crypto/asymmetric_keys/asymmetric_type.c
index b0e4ed23d668..1916680ad81b 100644
--- a/crypto/asymmetric_keys/asymmetric_type.c
+++ b/crypto/asymmetric_keys/asymmetric_type.c
@@ -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] = {
+	[VERIFYING_MODULE_SIGNATURE]		= "mod sig",
+	[VERIFYING_FIRMWARE_SIGNATURE]		= "firmware sig",
+	[VERIFYING_KEXEC_PE_SIGNATURE]		= "kexec PE sig",
+	[VERIFYING_KEY_SIGNATURE]		= "key sig",
+	[VERIFYING_KEY_SELF_SIGNATURE]		= "key self sig",
+	[VERIFYING_UNSPECIFIED_SIGNATURE]	= "unspec sig",
+};
+EXPORT_SYMBOL_GPL(key_being_used_for);
+
 static LIST_HEAD(asymmetric_key_parsers);
 static DECLARE_RWSEM(asymmetric_key_parsers_sem);
 
diff --git a/crypto/asymmetric_keys/pkcs7_key_type.c b/crypto/asymmetric_keys/pkcs7_key_type.c
index 6eae1a30b143..10d34dbd00b9 100644
--- a/crypto/asymmetric_keys/pkcs7_key_type.c
+++ b/crypto/asymmetric_keys/pkcs7_key_type.c
@@ -14,21 +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_want_authattrs;
-module_param_named(authattrs, pkcs7_want_authattrs, uint, S_IWUSR | S_IRUGO);
-MODULE_PARM_DESC(pkcs7_want_authattrs,
-		 "Whether or not a PKCS#7 message should contain authattrs (0-2)");
+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;
@@ -37,6 +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);
@@ -45,9 +52,7 @@ static int pkcs7_preparse(struct key_preparsed_payload *prep)
 		goto error;
 	}
 
-	if (pkcs7_want_authattrs > 2)
-		pkcs7_want_authattrs = 0;
-	ret = pkcs7_verify(pkcs7, pkcs7_want_authattrs);
+	ret = pkcs7_verify(pkcs7, usage);
 	if (ret < 0)
 		goto error_free;
 
diff --git a/crypto/asymmetric_keys/pkcs7_verify.c b/crypto/asymmetric_keys/pkcs7_verify.c
index 320f9a0b0ae9..d20c0b4b880e 100644
--- a/crypto/asymmetric_keys/pkcs7_verify.c
+++ b/crypto/asymmetric_keys/pkcs7_verify.c
@@ -346,7 +346,7 @@ static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
 /**
  * pkcs7_verify - Verify a PKCS#7 message
  * @pkcs7: The PKCS#7 message to be verified
- * @attr_style: Whether we want authenticatedAttributes or not.
+ * @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
@@ -358,6 +358,9 @@ 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:
  *
@@ -369,7 +372,8 @@ 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, enum pkcs7_attr_style attr_style)
+int pkcs7_verify(struct pkcs7_message *pkcs7,
+		 enum key_being_used_for usage)
 {
 	struct pkcs7_signed_info *sinfo;
 	struct x509_certificate *x509;
@@ -378,34 +382,42 @@ int pkcs7_verify(struct pkcs7_message *pkcs7, enum pkcs7_attr_style attr_style)
 
 	kenter("");
 
-	switch (attr_style) {
-	case PKCS7_REJECT_AUTHATTRS:
+	switch (usage) {
+	case VERIFYING_MODULE_SIGNATURE:
 		if (pkcs7->data_type != OID_data) {
-			pr_warn("Signed message is not ordinary data\n");
+			pr_warn("Invalid module sig (not pkcs7-data)\n");
 			return -EKEYREJECTED;
 		}
 		if (pkcs7->have_authattrs) {
-			pr_warn("Message contains unwanted authAttrs\n");
+			pr_warn("Invalid module sig (has authattrs)\n");
 			return -EKEYREJECTED;
 		}
 		break;
-	case PKCS7_REQUIRE_AUTHATTRS:
+	case VERIFYING_FIRMWARE_SIGNATURE:
 		if (pkcs7->data_type != OID_data) {
-			pr_warn("Signed message is not ordinary data\n");
+			pr_warn("Invalid firmware sig (not pkcs7-data)\n");
 			return -EKEYREJECTED;
 		}
 		if (!pkcs7->have_authattrs) {
-			pr_warn("Message does not contain authAttrs\n");
+			pr_warn("Invalid firmware sig (missing authattrs)\n");
 			return -EKEYREJECTED;
 		}
 		break;
-	case PKCS7_AUTHENTICODE_AUTHATTRS:
+	case VERIFYING_KEXEC_PE_SIGNATURE:
 		if (pkcs7->data_type != OID_msIndirectData) {
-			pr_warn("Signed message is not Authenticode\n");
+			pr_warn("Invalid kexec sig (not Authenticode)\n");
 			return -EKEYREJECTED;
 		}
 		/* Authattr presence checked in parser */
 		break;
+	case VERIFYING_UNSPECIFIED_SIGNATURE:
+		if (pkcs7->data_type != OID_data) {
+			pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
+			return -EKEYREJECTED;
+		}
+		break;
+	default:
+		return -EINVAL;
 	}
 
 	for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
diff --git a/crypto/asymmetric_keys/verify_pefile.c b/crypto/asymmetric_keys/verify_pefile.c
index d2044eeb72f4..897b734dabf9 100644
--- a/crypto/asymmetric_keys/verify_pefile.c
+++ b/crypto/asymmetric_keys/verify_pefile.c
@@ -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;
@@ -462,7 +465,7 @@ int verify_pefile_signature(const void *pebuf, unsigned pelen,
 	if (ret < 0)
 		goto error;
 
-	ret = pkcs7_verify(pkcs7, PKCS7_AUTHENTICODE_AUTHATTRS);
+	ret = pkcs7_verify(pkcs7, usage);
 	if (ret < 0)
 		goto error;
 
diff --git a/include/crypto/pkcs7.h b/include/crypto/pkcs7.h
index 15214059f408..441aff9b5aa7 100644
--- a/include/crypto/pkcs7.h
+++ b/include/crypto/pkcs7.h
@@ -12,6 +12,8 @@
 #ifndef _CRYPTO_PKCS7_H
 #define _CRYPTO_PKCS7_H
 
+#include <crypto/public_key.h>
+
 struct key;
 struct pkcs7_message;
 
@@ -36,13 +38,8 @@ extern int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
 /*
  * pkcs7_verify.c
  */
-enum pkcs7_attr_style {
-	PKCS7_REJECT_AUTHATTRS,
-	PKCS7_REQUIRE_AUTHATTRS,
-	PKCS7_AUTHENTICODE_AUTHATTRS,
-};
 extern int pkcs7_verify(struct pkcs7_message *pkcs7,
-			enum pkcs7_attr_style attr_style);
+			enum key_being_used_for usage);
 
 extern int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
 				      const void *data, size_t datalen);
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index fda097e079a4..067c242b1e15 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -40,6 +40,20 @@ enum pkey_id_type {
 extern const char *const pkey_id_type_name[PKEY_ID_TYPE__LAST];
 
 /*
+ * The use to which an asymmetric key is being put.
+ */
+enum key_being_used_for {
+	VERIFYING_MODULE_SIGNATURE,
+	VERIFYING_FIRMWARE_SIGNATURE,
+	VERIFYING_KEXEC_PE_SIGNATURE,
+	VERIFYING_KEY_SIGNATURE,
+	VERIFYING_KEY_SELF_SIGNATURE,
+	VERIFYING_UNSPECIFIED_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.
  *
  * Note that this may include private part of the key as well as the public
diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
index 9791c907cdb7..b20cd885c1fd 100644
--- a/include/keys/system_keyring.h
+++ b/include/keys/system_keyring.h
@@ -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)
@@ -30,7 +31,8 @@ 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);
+			      const void *raw_pkcs7, size_t pkcs7_len,
+			      enum key_being_used_for usage);
 #endif
 
 #endif /* _KEYS_SYSTEM_KEYRING_H */
diff --git a/include/linux/verify_pefile.h b/include/linux/verify_pefile.h
index ac34819214f9..da2049b5161c 100644
--- a/include/linux/verify_pefile.h
+++ b/include/linux/verify_pefile.h
@@ -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 */
diff --git a/kernel/module_signing.c b/kernel/module_signing.c
index 70ad463f6df0..bd62f5cda746 100644
--- a/kernel/module_signing.c
+++ b/kernel/module_signing.c
@@ -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);
+	return system_verify_data(mod, modlen, mod + modlen, sig_len,
+				  VERIFYING_MODULE_SIGNATURE);
 }
diff --git a/kernel/system_keyring.c b/kernel/system_keyring.c
index f9e1a75db59b..2570598b784d 100644
--- a/kernel/system_keyring.c
+++ b/kernel/system_keyring.c
@@ -113,9 +113,11 @@ 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.
  */
 int system_verify_data(const void *data, unsigned long len,
-		       const void *raw_pkcs7, size_t pkcs7_len)
+		       const void *raw_pkcs7, size_t pkcs7_len,
+		       enum key_being_used_for usage)
 {
 	struct pkcs7_message *pkcs7;
 	bool trusted;
@@ -132,7 +134,7 @@ int system_verify_data(const void *data, unsigned long len,
 		goto error;
 	}
 
-	ret = pkcs7_verify(pkcs7, PKCS7_REJECT_AUTHATTRS);
+	ret = pkcs7_verify(pkcs7, usage);
 	if (ret < 0)
 		goto error;