[PATCH 2/4] PKCS#7: Check codeSigning EKU for kernel module and kexec pe verification

Lee, Chun-Yi
2021-01-20T09:13:09Z

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

Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>
---
certs/system_keyring.c | 2 +-
crypto/asymmetric_keys/Kconfig | 9 +++++++++
crypto/asymmetric_keys/pkcs7_trust.c | 37 +++++++++++++++++++++++++++++++++---
include/crypto/pkcs7.h | 3 ++-
4 files changed, 46 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..1754812df989 100644
--- a/crypto/asymmetric_keys/Kconfig
+++ b/crypto/asymmetric_keys/Kconfig
@@ -96,4 +96,13 @@ 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 when verifying the signature in PKCS#7. It affects kernel
+ module verification and kexec PE binary verification.
+
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