[RFC PATCH] ima-evm-utils: Allow manual setting keyid for signing

[Vitaly Chikunov <vt@altlinux.org>]

Allow user to set signature's keyid using `--keyid' option. Keyid should
correspond to SKID in certificate, when keyid is calculated using SHA-1
in libimaevm it may mismatch keyid extracted by the kernel from SKID of
certificate (the way public key is presented to the kernel), thus making
signatures not verifiable. This may happen when certificate is using non
SHA-1 SKID (see rfc7093) or just 'unique number' (see rfc5280 4.2.1.2).
As a last resort user may specify arbitrary keyid using the new option.

This commit creates backward compatible ABI change for libimaevm,
because of adding additional parameter to imaevm_params - older
libimaevm can work with newer client.

Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
---
 README          |  1 +
 src/evmctl.c    | 15 +++++++++++++++
 src/imaevm.h    |  1 +
 src/libimaevm.c |  7 ++++---
 4 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/README b/README
index 321045d..8cd66e0 100644
--- a/README
+++ b/README
@@ -48,6 +48,7 @@ OPTIONS
       --xattr-user   store xattrs in user namespace (for testing purposes)
       --rsa          use RSA key type and signing scheme v1
   -k, --key          path to signing key (default: /etc/keys/{privkey,pubkey}_evm.pem)
+      --keyid val    overwrite signature keyid with a value (for signing)
   -o, --portable     generate portable EVM signatures
   -p, --pass         password for encrypted signing key
   -r, --recursive    recurse into directories (sign)
diff --git a/src/evmctl.c b/src/evmctl.c
index 1815f55..83b228a 100644
--- a/src/evmctl.c
+++ b/src/evmctl.c
@@ -42,6 +42,7 @@
 #include <sys/param.h>
 #include <sys/stat.h>
 #include <sys/ioctl.h>
+#include <arpa/inet.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <stdlib.h>
@@ -2446,6 +2447,7 @@ static void usage(void)
 		"      --xattr-user   store xattrs in user namespace (for testing purposes)\n"
 		"      --rsa          use RSA key type and signing scheme v1\n"
 		"  -k, --key          path to signing key (default: /etc/keys/{privkey,pubkey}_evm.pem)\n"
+		"      --keyid val    overwrite signature keyid with a value (for signing)\n"
 		"  -o, --portable     generate portable EVM signatures\n"
 		"  -p, --pass         password for encrypted signing key\n"
 		"  -r, --recursive    recurse into directories (sign)\n"
@@ -2525,6 +2527,7 @@ static struct option opts[] = {
 	{"xattr-user", 0, 0, 140},
 	{"ignore-violations", 0, 0, 141},
 	{"pcrs", 1, 0, 142},
+	{"keyid", 1, 0, 143},
 	{}
 
 };
@@ -2569,6 +2572,8 @@ int main(int argc, char *argv[])
 {
 	int err = 0, c, lind;
 	ENGINE *eng = NULL;
+	unsigned long int keyid;
+	char *eptr;
 
 #if !(OPENSSL_VERSION_NUMBER < 0x10100000)
 	OPENSSL_init_crypto(
@@ -2713,6 +2718,16 @@ int main(int argc, char *argv[])
 			}
 			pcrfile[npcrfile++] = optarg;
 			break;
+		case 143:
+			errno = 0;
+			keyid = strtoul(optarg, &eptr, 16);
+			if (errno || eptr - optarg != strlen(optarg) ||
+			    keyid > UINT_MAX || keyid == 0) {
+				log_err("Invalid keyid value.\n");
+				exit(1);
+			}
+			imaevm_params.keyid = htonl(keyid);
+			break;
 		case '?':
 			exit(1);
 			break;
diff --git a/src/imaevm.h b/src/imaevm.h
index 4503919..9f38059 100644
--- a/src/imaevm.h
+++ b/src/imaevm.h
@@ -196,6 +196,7 @@ struct libimaevm_params {
 	const char *hash_algo;
 	const char *keyfile;
 	const char *keypass;
+	uint32_t keyid;		/* keyid overriding value, unless 0. */
 };
 
 struct RSA_ASN1_template {
diff --git a/src/libimaevm.c b/src/libimaevm.c
index fa6c278..070cd97 100644
--- a/src/libimaevm.c
+++ b/src/libimaevm.c
@@ -894,7 +894,6 @@ static int sign_hash_v2(const char *algo, const unsigned char *hash,
 	const EVP_MD *md;
 	size_t sigsize;
 	const char *st;
-	uint32_t keyid;
 
 	if (!hash) {
 		log_err("sign_hash_v2: hash is null\n");
@@ -932,8 +931,10 @@ static int sign_hash_v2(const char *algo, const unsigned char *hash,
 		return -1;
 	}
 
-	calc_keyid_v2(&keyid, name, pkey);
-	hdr->keyid = keyid;
+	if (imaevm_params.keyid)
+		hdr->keyid = imaevm_params.keyid;
+	else
+		calc_keyid_v2(&hdr->keyid, name, pkey);
 
 	st = "EVP_PKEY_CTX_new";
 	if (!(ctx = EVP_PKEY_CTX_new(pkey, NULL)))
-- 
2.11.0