linux-kernel - [RFC PATCH 2/2] PKCS#7: Check codeSigning EKU for kernel module and kexec pe verification

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Message-Id: <20201020065001.13836-3-jlee@suse.com>
Date:   Tue, 20 Oct 2020 14:50:01 +0800
From:   "Lee, Chun-Yi" <joeyli.kernel@...il.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>, keyrings@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Lee, Chun-Yi" <jlee@...e.com>
Subject: [RFC PATCH 2/2] PKCS#7: Check codeSigning EKU for kernel module and kexec pe verification

This patch adds the logic for checking the CodeSigning extended
key usage extenstion when verifying signature of kernel module or
kexec PE binary in PKCS#7.

Signed-off-by: "Lee, Chun-Yi" <jlee@...e.com>
---
 certs/system_keyring.c               |  2 +-
 crypto/asymmetric_keys/Kconfig       | 10 ++++++++++
 crypto/asymmetric_keys/pkcs7_trust.c | 37 +++++++++++++++++++++++++++++++++---
 include/crypto/pkcs7.h               |  3 ++-
 4 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/certs/system_keyring.c b/certs/system_keyring.c
index 798291177186..4104f5465d8a 100644
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -242,7 +242,7 @@ int verify_pkcs7_message_sig(const void *data, size_t len,
 			goto error;
 		}
 	}
-	ret = pkcs7_validate_trust(pkcs7, trusted_keys);
+	ret = pkcs7_validate_trust(pkcs7, trusted_keys, usage);
 	if (ret < 0) {
 		if (ret == -ENOKEY)
 			pr_devel("PKCS#7 signature not signed with a trusted key\n");
diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
index 1f1f004dc757..6e3de0c3b5f0 100644
--- a/crypto/asymmetric_keys/Kconfig
+++ b/crypto/asymmetric_keys/Kconfig
@@ -96,4 +96,14 @@ config SIGNED_PE_FILE_VERIFICATION
 	  This option provides support for verifying the signature(s) on a
 	  signed PE binary.
 
+config CHECK_CODESIGN_EKU
+	bool "Check codeSigning extended key usage"
+	depends on PKCS7_MESSAGE_PARSER=y
+	depends on SYSTEM_DATA_VERIFICATION
+	help
+	  This option provides support for checking the codeSigning extended
+	  key usage extension when verifying the signature in PKCS#7. It
+	  affects kernel module verification and kexec PE binary verification
+	  now.
+
 endif # ASYMMETRIC_KEY_TYPE
diff --git a/crypto/asymmetric_keys/pkcs7_trust.c b/crypto/asymmetric_keys/pkcs7_trust.c
index 61af3c4d82cc..1d2318ff63db 100644
--- a/crypto/asymmetric_keys/pkcs7_trust.c
+++ b/crypto/asymmetric_keys/pkcs7_trust.c
@@ -16,12 +16,36 @@
 #include <crypto/public_key.h>
 #include "pkcs7_parser.h"
 
+#ifdef CONFIG_CHECK_CODESIGN_EKU
+static bool check_codesign_eku(struct key *key,
+			     enum key_being_used_for usage)
+{
+	struct public_key *public_key = key->payload.data[asym_crypto];
+
+	switch (usage) {
+	case VERIFYING_MODULE_SIGNATURE:
+	case VERIFYING_KEXEC_PE_SIGNATURE:
+		return !!(public_key->eku & EKU_codeSigning);
+	default:
+		break;
+	}
+	return true;
+}
+#else
+static bool check_codesign_eku(struct key *key,
+			     enum key_being_used_for usage)
+{
+	return true;
+}
+#endif
+
 /**
  * Check the trust on one PKCS#7 SignedInfo block.
  */
 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;
@@ -112,6 +136,12 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
 	return -ENOKEY;
 
 matched:
+	if (!check_codesign_eku(key, usage)) {
+		pr_warn("sinfo %u: The signer %x key is not CodeSigning\n",
+			sinfo->index, key_serial(key));
+		key_put(key);
+		return -ENOKEY;
+	}
 	ret = verify_signature(key, sig);
 	key_put(key);
 	if (ret < 0) {
@@ -156,7 +186,8 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
  * May also return -ENOMEM.
  */
 int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
-			 struct key *trust_keyring)
+			 struct key *trust_keyring,
+			 enum key_being_used_for usage)
 {
 	struct pkcs7_signed_info *sinfo;
 	struct x509_certificate *p;
@@ -167,7 +198,7 @@ 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;
diff --git a/include/crypto/pkcs7.h b/include/crypto/pkcs7.h
index 38ec7f5f9041..b3b48240ba73 100644
--- a/include/crypto/pkcs7.h
+++ b/include/crypto/pkcs7.h
@@ -30,7 +30,8 @@ extern int pkcs7_get_content_data(const struct pkcs7_message *pkcs7,
  * pkcs7_trust.c
  */
 extern int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
-				struct key *trust_keyring);
+				struct key *trust_keyring,
+				enum key_being_used_for usage);
 
 /*
  * pkcs7_verify.c
-- 
2.16.4