[PATCH v3 1/2] ima_evm_utils: erroneous "verification failed: 0 (invalid padding)" message

[Mimi Zohar <zohar@linux.ibm.com>]

When public keys are specified on the boot command line (--key <public
key file>, [<public key file>, ...]), the appropriate public key is used
to verify EVM or file signatures.  If no keys are specified, the default
x509_evm.der or x509_evm.pem file is used to verify the DIGSIG_VERSION_2
or DIGSIG_VERSION_1 signatures respectively, without first checking the
keyids.  Instead of emitting a "verification failed: 0 (invalid
padding)" message, an "unknown keyid" message would be clearer.

To address this problem, when no public keys are specified, this patch
loads the x509_evm.der default public key onto the "public_keys" list,
while the x509_evm.pem continues to be passed to verify_hash_v1().  As a
result of this change, the verify_hash_v2() "key" parameter is
unnecssary and is removed.

Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
---
 src/evmctl.c    | 14 +++++++++++---
 src/libimaevm.c | 56 ++++++++++++++++++++++----------------------------------
 2 files changed, 33 insertions(+), 37 deletions(-)

diff --git a/src/evmctl.c b/src/evmctl.c
index 61808d276419..9e0926f10404 100644
--- a/src/evmctl.c
+++ b/src/evmctl.c
@@ -838,6 +838,11 @@ static int cmd_verify_evm(struct command *cmd)
 		return -1;
 	}
 
+	if (params.keyfile)	/* Support multiple public keys */
+		init_public_keys(params.keyfile);
+	else			/* assume read pubkey from x509 cert */
+		init_public_keys("/etc/keys/x509_evm.der");
+
 	err = verify_evm(file);
 	if (!err && params.verbose >= LOG_INFO)
 		log_info("%s: verification is OK\n", file);
@@ -879,8 +884,10 @@ static int cmd_verify_ima(struct command *cmd)
 	char *file = g_argv[optind++];
 	int err;
 
-	if (params.keyfile)
+	if (params.keyfile)	/* Support multiple public keys */
 		init_public_keys(params.keyfile);
+	else			/* assume read pubkey from x509 cert */
+		init_public_keys("/etc/keys/x509_evm.der");
 
 	errno = 0;
 	if (!file) {
@@ -1602,9 +1609,10 @@ static int ima_measurement(const char *file)
 		return -1;
 	}
 
-	/* Support multiple public keys */
-	if (params.keyfile)
+	if (params.keyfile)	/* Support multiple public keys */
 		init_public_keys(params.keyfile);
+	else			/* assume read pubkey from x509 cert */
+		init_public_keys("/etc/keys/x509_evm.der");
 
 	while (fread(&entry.header, sizeof(entry.header), 1, fp)) {
 		ima_extend_pcr(pcr[entry.header.pcr], entry.header.digest,
diff --git a/src/libimaevm.c b/src/libimaevm.c
index ae487f9fe36c..43eb4ef2412c 100644
--- a/src/libimaevm.c
+++ b/src/libimaevm.c
@@ -302,6 +302,9 @@ EVP_PKEY *read_pub_pkey(const char *keyfile, int x509)
 	X509 *crt = NULL;
 	EVP_PKEY *pkey = NULL;
 
+	if (!keyfile)
+		return NULL;
+
 	fp = fopen(keyfile, "r");
 	if (!fp) {
 		log_err("Failed to open keyfile: %s\n", keyfile);
@@ -348,8 +351,8 @@ RSA *read_pub_key(const char *keyfile, int x509)
 	return key;
 }
 
-int verify_hash_v1(const char *file, const unsigned char *hash, int size,
-		   unsigned char *sig, int siglen, const char *keyfile)
+static int verify_hash_v1(const char *file, const unsigned char *hash, int size,
+			  unsigned char *sig, int siglen, const char *keyfile)
 {
 	int err, len;
 	SHA_CTX ctx;
@@ -449,12 +452,13 @@ void init_public_keys(const char *keyfiles)
 /*
  * Return: 0 verification good, 1 verification bad, -1 error.
  */
-int verify_hash_v2(const char *file, const unsigned char *hash, int size,
-		   unsigned char *sig, int siglen, const char *keyfile)
+static int verify_hash_v2(const char *file, const unsigned char *hash, int size,
+			  unsigned char *sig, int siglen)
 {
 	int ret = -1;
 	EVP_PKEY *pkey, *pkey_free = NULL;
 	struct signature_v2_hdr *hdr = (struct signature_v2_hdr *)sig;
+	uint32_t keyid = hdr->keyid;
 	EVP_PKEY_CTX *ctx;
 	const EVP_MD *md;
 	const char *st;
@@ -464,20 +468,11 @@ int verify_hash_v2(const char *file, const unsigned char *hash, int size,
 		log_dump(hash, size);
 	}
 
-	if (public_keys) {
-		uint32_t keyid = hdr->keyid;
-
-		pkey = find_keyid(keyid);
-		if (!pkey) {
-			log_err("%s: unknown keyid: %x\n", file,
-				__be32_to_cpup(&keyid));
-			return -1;
-		}
-	} else {
-		pkey = read_pub_pkey(keyfile, 1);
-		if (!pkey)
-			return -1;
-		pkey_free = pkey;
+	pkey = find_keyid(keyid);
+	if (!pkey) {
+		log_err("%s: unknown keyid: %x\n",
+			file, __be32_to_cpup(&keyid));
+		return -1;
 	}
 
 	st = "EVP_PKEY_CTX_new";
@@ -569,28 +564,21 @@ static int get_hash_algo_from_sig(unsigned char *sig)
 int verify_hash(const char *file, const unsigned char *hash, int size, unsigned char *sig,
 		int siglen)
 {
-	const char *key;
-	int x509;
-	verify_hash_fn_t verify_hash;
+	const char *key = NULL;
 
 	/* Get signature type from sig header */
 	if (sig[0] == DIGSIG_VERSION_1) {
-		verify_hash = verify_hash_v1;
+
 		/* Read pubkey from RSA key */
-		x509 = 0;
-	} else if (sig[0] == DIGSIG_VERSION_2) {
-		verify_hash = verify_hash_v2;
-		/* Read pubkey from x509 cert */
-		x509 = 1;
-	} else
-		return -1;
+		if (!params.keyfile)
+			key = "/etc/keys/pubkey_evm.pem";
+		return verify_hash_v1(file, hash, size, sig, siglen, key);
+	}
 
-	/* Determine what key to use for verification*/
-	key = params.keyfile ? : x509 ?
-			"/etc/keys/x509_evm.der" :
-			"/etc/keys/pubkey_evm.pem";
+	if (sig[0] == DIGSIG_VERSION_2)
+		return verify_hash_v2(file, hash, size, sig, siglen);
 
-	return verify_hash(file, hash, size, sig, siglen, key);
+	return -1;
 }
 
 int ima_verify_signature(const char *file, unsigned char *sig, int siglen,
-- 
2.7.5