Re: [PATCH v2 1/3] ima-evm-utils: Allow manual setting keyid for signing

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On 5/4/21 12:33 AM, Vitaly Chikunov wrote:
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@xxxxxxxxxxxx>
Reported-by: Elvira Khabirova <lineprinter0@xxxxxxxxx>
---
  README                 |  1 +
  src/evmctl.c           | 14 ++++++++++++++
  src/imaevm.h           |  1 +
  src/libimaevm.c        |  8 +++++---
  tests/sign_verify.test |  1 +
  5 files changed, 22 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..7983299 100644
--- a/src/evmctl.c
+++ b/src/evmctl.c
@@ -2446,6 +2446,7 @@ 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 +2526,7 @@ static struct option opts[] = {
  	{"xattr-user", 0, 0, 140},
  	{"ignore-violations", 0, 0, 141},
  	{"pcrs", 1, 0, 142},
+	{"keyid", 1, 0, 143},
  	{}
};
@@ -2569,6 +2571,8 @@ 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 +2717,16 @@ 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 = 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..481d29d 100644
--- a/src/libimaevm.c
+++ b/src/libimaevm.c
@@ -45,6 +45,7 @@
  #include <sys/param.h>
  #include <sys/stat.h>
  #include <asm/byteorder.h>
+#include <arpa/inet.h>
  #include <unistd.h>
  #include <dirent.h>
  #include <string.h>
@@ -894,7 +895,6 @@ 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 +932,10 @@ 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 = htonl(imaevm_params.keyid);


Nit: Since existing code uses __be32_to_cpup I would use __cpu_to_be32 here.


+	else
+		calc_keyid_v2(&hdr->keyid, name, pkey);
st = "EVP_PKEY_CTX_new";
  	if (!(ctx = EVP_PKEY_CTX_new(pkey, NULL)))
diff --git a/tests/sign_verify.test b/tests/sign_verify.test
index 288e133..2c21812 100755
--- a/tests/sign_verify.test
+++ b/tests/sign_verify.test
@@ -359,6 +359,7 @@ sign_verify  rsa1024  sha256  0x0301 --rsa
  sign_verify  rsa1024  md5     0x030201:K:0080
  sign_verify  rsa1024  sha1    0x030202:K:0080
  sign_verify  rsa1024  sha224  0x030207:K:0080
+expect_pass check_sign TYPE=ima KEY=rsa1024 ALG=sha256 PREFIX=0x030204aabbccdd0080 OPTS=--keyid=aabbccdd
  sign_verify  rsa1024  sha256  0x030204:K:0080
    try_different_keys
    try_different_sigs


Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>




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