[PATCH v2 ima-evm-utils 1/3] initialize errno in cmd_sign_hash()

[PATCH v2 ima-evm-utils 1/3] initialize errno in cmd_sign_hash()

[Mimi Zohar]

Prevent "errno: No such file or directory (2)" message.

Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
---
 src/evmctl.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/evmctl.c b/src/evmctl.c
index 8bdd34817408..ca9449498321 100644
--- a/src/evmctl.c
+++ b/src/evmctl.c
@@ -737,6 +737,7 @@ static int cmd_sign_hash(struct command *cmd)
 	unsigned char sig[MAX_SIGNATURE_SIZE] = "\x03";
 	int siglen;
 
+	errno = 0;
 	key = imaevm_params.keyfile ? : "/etc/keys/privkey_evm.pem";
 
 	/* support reading hash (eg. output of shasum) */
-- 
2.27.0

[PATCH v2 ima-evm-utils 2/3] Sign an fs-verity file digest

[Mimi Zohar]

Sign fs-verity file digests provided in the format as produced by
"fsverity measure".  The output is of the same format as the input,
but with the file signature appended.  Use setfattr to write the
signature as security.ima xattr.

fsverity measure format: <algo>:<hash> <pathname>
output format: <algo>:<hash> <pathname> <signature>

Instead of directly signing the fsverity hash, to disambiguate the
original IMA signatures from the fs-verity signatures stored in the
security.ima xattr a new signature format version 3 (sigv3) was
defined as the hash of the xattr type (enum evm_ima_xattr_type),
the hash algorithm (enum hash_algo), and the hash.

Example:
fsverity measure <pathname> | evmctl sign_hash --veritysig \
 --key <pem encoded private key>

Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
---
 README          |   3 +-
 src/evmctl.c    | 103 +++++++++++++++++++++++++++++++++++++++++-------
 src/imaevm.h    |   5 ++-
 src/libimaevm.c |  85 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 179 insertions(+), 17 deletions(-)

diff --git a/README b/README
index 5b5ecb52a74b..ffe46ad75728 100644
--- a/README
+++ b/README
@@ -34,7 +34,7 @@ COMMANDS
  ima_hash file
  ima_measurement [--ignore-violations] [--verify-sig [--key "key1, key2, ..."]]  [--pcrs [hash-algorithm,]file [--pcrs hash-algorithm,file] ...] file
  ima_fix [-t fdsxm] path
- sign_hash [--key key] [--pass password]
+ sign_hash [--veritysig] [--key key] [--pass password]
  hmac [--imahash | --imasig ] file
 
 
@@ -43,6 +43,7 @@ OPTIONS
 
   -a, --hashalgo     sha1, sha224, sha256, sha384, sha512
   -s, --imasig       make IMA signature
+      --veritysig    sign an fs-verity file digest hash
   -d, --imahash      make IMA hash
   -f, --sigfile      store IMA signature in .sig file instead of xattr
       --xattr-user   store xattrs in user namespace (for testing purposes)
diff --git a/src/evmctl.c b/src/evmctl.c
index ca9449498321..9152b0a5c7c2 100644
--- a/src/evmctl.c
+++ b/src/evmctl.c
@@ -135,6 +135,7 @@ static int msize;
 static dev_t fs_dev;
 static bool evm_immutable;
 static bool evm_portable;
+static bool veritysig;
 
 #define HMAC_FLAG_NO_UUID	0x0001
 #define HMAC_FLAG_CAPS_SET	0x0002
@@ -726,34 +727,102 @@ static int cmd_sign_ima(struct command *cmd)
 	return do_cmd(cmd, sign_ima_file);
 }
 
+/*
+ * Sign file hash(es) provided in the format as produced by either
+ * sha*sum or "fsverity measure".
+ *
+ * sha*sum format: <hash> <pathname>
+ * fsverity measure format: <algo>:<hash> <pathname>
+ *
+ * To disambiguate the resulting file signatures, a new signature format
+ * version 3 (sigv3) was defined as the hash of the xattr type (enum
+ * evm_ima_xattr_type), the hash algorithm (enum hash_algo), and the hash.
+ *
+ * Either directly sign the sha*sum hash or indirectly sign the fsverity
+ * hash (sigv3).
+ *
+ * The output is the same format as the input with the resulting file
+ * signature appended.
+ */
 static int cmd_sign_hash(struct command *cmd)
 {
+	unsigned char sigv3_hash[MAX_DIGEST_SIZE];
+	unsigned char sig[MAX_SIGNATURE_SIZE];
+	unsigned char hash[MAX_DIGEST_SIZE];
+	int siglen, algolen, hashlen = 0;
+	char *line = NULL, *token, *hashp;
+	size_t line_len = 0;
 	const char *key;
-	char *token, *line = NULL;
-	int hashlen = 0;
-	size_t line_len;
+	char algo[12];
 	ssize_t len;
-	unsigned char hash[MAX_DIGEST_SIZE];
-	unsigned char sig[MAX_SIGNATURE_SIZE] = "\x03";
-	int siglen;
+	int ret;
 
 	errno = 0;
 	key = imaevm_params.keyfile ? : "/etc/keys/privkey_evm.pem";
 
-	/* support reading hash (eg. output of shasum) */
 	while ((len = getline(&line, &line_len, stdin)) > 0) {
 		/* remove end of line */
 		if (line[len - 1] == '\n')
 			line[--len] = '\0';
 
-		/* find the end of the hash */
-		token = strpbrk(line, ", \t");
-		hashlen = token ? token - line : strlen(line);
+		/*
+		 * Before either directly or indirectly signing the hash,
+		 * convert the hex-ascii hash representation to binary.
+		 */
+		if (veritysig) {
+
+			/* split the algorithm from the hash */
+			hashp = strpbrk(line, ":");
+			if (!hashp) {	/* pointer to the delimiter */
+				log_err("Missing fsverity hash algorithm\n");
+				continue;
+			}
+
+			algolen = hashp - line;
+			if (algolen > sizeof(algo))
+				algolen = sizeof(algo);
+			if (algolen <= 0) {
+				log_err("Missing fsverity hash algorithm\n");
+				continue;
+			}
+
+			strncpy(algo, line, algolen);
+			algo[algolen] = 0;	/* Nul terminate algorithm */
+
+			hashp++;
+			token = strpbrk(line, ", \t");
+			hashlen = token - hashp;
+			if (hashlen <= 0) {
+				log_err("Missing fsverity hash\n");
+				continue;
+			}
+
+			assert(hashlen / 2 <= sizeof(hash));
+			hex2bin(hash, hashp, hashlen / 2);
+
+			ret = calc_hash_sigv3(IMA_VERITY_DIGSIG, algo, hash,
+					      sigv3_hash);
+			if (ret < 0 || ret == 1) {
+				log_info("Failure to calculate fs-verity hash\n");
+				continue;
+			}
+
+			siglen = sign_hash(algo, sigv3_hash, hashlen / 2,
+					   key, NULL, sig + 1);
+
+			sig[0] = IMA_VERITY_DIGSIG;
+			sig[1] = DIGSIG_VERSION_3;	/* sigv3 */
+		} else {
+			token = strpbrk(line, ", \t");
+			hashlen = token ? token - line : strlen(line);
+			assert(hashlen / 2 <= sizeof(hash));
+			hex2bin(hash, line, hashlen / 2);
+
+			siglen = sign_hash(imaevm_params.hash_algo, hash,
+					   hashlen / 2, key, NULL, sig + 1);
+			sig[0] = EVM_IMA_XATTR_DIGSIG;
+		}
 
-		assert(hashlen / 2 <= sizeof(hash));
-		hex2bin(hash, line, hashlen / 2);
-		siglen = sign_hash(imaevm_params.hash_algo, hash, hashlen / 2,
-				 key, NULL, sig + 1);
 		if (siglen <= 1)
 			return siglen;
 		assert(siglen < sizeof(sig));
@@ -2557,7 +2626,7 @@ struct command cmds[] = {
 	{"ima_boot_aggregate", cmd_ima_bootaggr, 0, "[--pcrs hash-algorithm,file] [TPM 1.2 BIOS event log]", "Calculate per TPM bank boot_aggregate digests\n"},
 	{"ima_fix", cmd_ima_fix, 0, "[-t fdsxm] path", "Recursively fix IMA/EVM xattrs in fix mode.\n"},
 	{"ima_clear", cmd_ima_clear, 0, "[-t fdsxm] path", "Recursively remove IMA/EVM xattrs.\n"},
-	{"sign_hash", cmd_sign_hash, 0, "[--key key] [--pass [password]", "Sign hashes from shaXsum output.\n"},
+	{"sign_hash", cmd_sign_hash, 0, "[--veritysig] [--key key] [--pass [password]", "Sign hashes from either shaXsum or \"fsverity measure\" output.\n"},
 #ifdef DEBUG
 	{"hmac", cmd_hmac_evm, 0, "[--imahash | --imasig ] file", "Sign file metadata with HMAC using symmetric key (for testing purpose).\n"},
 #endif
@@ -2597,6 +2666,7 @@ static struct option opts[] = {
 	{"verify-bank", 2, 0, 143},
 	{"keyid", 1, 0, 144},
 	{"keyid-from-cert", 1, 0, 145},
+	{"veritysig", 0, 0, 146},
 	{}
 
 };
@@ -2827,6 +2897,9 @@ int main(int argc, char *argv[])
 			}
 			imaevm_params.keyid = keyid;
 			break;
+		case 146:
+			veritysig = 1;
+			break;
 		case '?':
 			exit(1);
 			break;
diff --git a/src/imaevm.h b/src/imaevm.h
index 0d53a0232ae4..afcf1e042014 100644
--- a/src/imaevm.h
+++ b/src/imaevm.h
@@ -93,6 +93,7 @@ enum evm_ima_xattr_type {
 	EVM_IMA_XATTR_DIGSIG,
 	IMA_XATTR_DIGEST_NG,
 	EVM_XATTR_PORTABLE_DIGSIG,
+	IMA_VERITY_DIGSIG,
 };
 
 struct h_misc {
@@ -138,7 +139,8 @@ enum digest_algo {
 
 enum digsig_version {
 	DIGSIG_VERSION_1 = 1,
-	DIGSIG_VERSION_2
+	DIGSIG_VERSION_2,
+	DIGSIG_VERSION_3	/* hash of ima_file_id struct (portion used) */
 };
 
 struct pubkey_hdr {
@@ -233,5 +235,6 @@ int ima_verify_signature(const char *file, unsigned char *sig, int siglen, unsig
 void init_public_keys(const char *keyfiles);
 int imaevm_hash_algo_from_sig(unsigned char *sig);
 const char *imaevm_hash_algo_by_id(int algo);
+int calc_hash_sigv3(enum evm_ima_xattr_type type, const char *algo, const unsigned char *in_hash, unsigned char *out_hash);
 
 #endif
diff --git a/src/libimaevm.c b/src/libimaevm.c
index 388b726f1e3a..7c2ed5fb0556 100644
--- a/src/libimaevm.c
+++ b/src/libimaevm.c
@@ -495,6 +495,91 @@ err:
 	return ret;
 }
 
+#define HASH_MAX_DIGESTSIZE 512
+
+struct ima_file_id {
+	__u8 hash_type;		/* xattr type [enum evm_ima_xattr_type] */
+	__u8 hash_algorithm;	/* Digest algorithm [enum hash_algo] */
+	__u8 hash[HASH_MAX_DIGESTSIZE];
+} __packed;
+
+/*
+ * Calculate the signature format version 3 hash based on the portion
+ * of the ima_file_id structure used, not the entire structure.
+ *
+ * For openssl errors return 1, other errors return -EINVAL.
+ */
+int calc_hash_sigv3(enum evm_ima_xattr_type type, const char *algo,
+		    const unsigned char *in_hash, unsigned char *out_hash)
+{
+	struct ima_file_id file_id = { .hash_type = IMA_VERITY_DIGSIG };
+	uint8_t *data = (uint8_t *) &file_id;
+
+	const EVP_MD *md;
+	EVP_MD_CTX *pctx;
+	unsigned int mdlen;
+	int err;
+#if OPENSSL_VERSION_NUMBER < 0x10100000
+	EVP_MD_CTX ctx;
+	pctx = &ctx;
+#else
+	pctx = EVP_MD_CTX_new();
+#endif
+	int hash_algo;
+	int hash_size;
+	unsigned int unused;
+
+	if (type != IMA_VERITY_DIGSIG) {
+		log_err("Only fsverity supports signature format v3 (sigv3)\n");
+		return -EINVAL;
+	}
+
+	if ((hash_algo = imaevm_get_hash_algo(algo)) < 0) {
+		log_err("Hash algorithm %s not supported\n", algo);
+		return -EINVAL;
+	}
+	file_id.hash_algorithm = hash_algo;
+
+	md = EVP_get_digestbyname(algo);
+	if (!md) {
+		log_err("EVP_get_digestbyname(%s) failed\n", algo);
+		err = 1;
+		goto err;
+	}
+
+	hash_size = EVP_MD_size(md);
+	memcpy(file_id.hash, in_hash, hash_size);
+
+	err = EVP_DigestInit(pctx, md);
+	if (!err) {
+		log_err("EVP_DigestInit() failed\n");
+		err = 1;
+		goto err;
+	}
+
+	unused = HASH_MAX_DIGESTSIZE - hash_size;
+	if (!EVP_DigestUpdate(pctx, data, sizeof(file_id) - unused)) {
+		log_err("EVP_DigestUpdate() failed\n");
+		err = 1;
+		goto err;
+	}
+
+	err = EVP_DigestFinal(pctx, out_hash, &mdlen);
+	if (!err) {
+		log_err("EVP_DigestFinal() failed\n");
+		err = 1;
+		goto err;
+	}
+	err = mdlen;
+err:
+	if (err == 1)
+		output_openssl_errors();
+#if OPENSSL_VERSION_NUMBER >= 0x10100000
+	EVP_MD_CTX_free(pctx);
+#endif
+	return err;
+}
+
 int imaevm_get_hash_algo(const char *algo)
 {
 	int i;
-- 
2.27.0

[PATCH v2 ima-evm-utils 3/3] Verify an fs-verity file digest based signature

[Mimi Zohar]

ima-evm-utils does not attempt to calculate or even read the fs-verity
file hash, but can verify the fs-verity signature based on the fsverity
file hash, both contained in the measurement list record.

For the time being only fs-verity supports signature format v3 (sigv3).
To differentiate between the existing IMA and fs-verity file signatures,
modify the verify_hash() 'sig' argument to be a pointer to the entire
xattr, including the xattr type.

Example:
evmctl ima_measurement --key <DER encoded public key> \
 --verify-sig /sys/kernel/security/ima/binary_runtime_measurements

Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
---
 src/evmctl.c    | 11 +++++++++--
 src/libimaevm.c | 50 +++++++++++++++++++++++++++++++++++++------------
 2 files changed, 47 insertions(+), 14 deletions(-)

diff --git a/src/evmctl.c b/src/evmctl.c
index 9152b0a5c7c2..593eed80f96a 100644
--- a/src/evmctl.c
+++ b/src/evmctl.c
@@ -909,7 +909,7 @@ static int verify_evm(const char *file)
 		return mdlen;
 	assert(mdlen <= sizeof(hash));
 
-	return verify_hash(file, hash, mdlen, sig + 1, len - 1);
+	return verify_hash(file, hash, mdlen, sig, len);
 }
 
 static int cmd_verify_evm(struct command *cmd)
@@ -1572,7 +1572,8 @@ void ima_ng_show(struct template_entry *entry)
 	fieldp += field_len;
 	total_len -= field_len;
 
-	if (!strcmp(entry->name, "ima-sig")) {
+	if (!strcmp(entry->name, "ima-sig") ||
+	    !strcmp(entry->name, "ima-sigv2")) {
 		/* get signature */
 		field_len = *(uint32_t *)fieldp;
 		fieldp += sizeof(field_len);
@@ -1618,11 +1619,17 @@ void ima_ng_show(struct template_entry *entry)
 			log_info(" ");
 			log_dump(sig, sig_len);
 		}
+
+		/*
+		 * Either verify the signature against the hash contained in
+		 * the measurement list or calculate the hash.
+		 */
 		if (verify_list_sig)
 			err = ima_verify_signature(path, sig, sig_len,
 						   digest, digest_len);
 		else
 			err = ima_verify_signature(path, sig, sig_len, NULL, 0);
+
 		if (!err && imaevm_params.verbose > LOG_INFO)
 			log_info("%s: verification is OK\n", path);
 	} else {
diff --git a/src/libimaevm.c b/src/libimaevm.c
index 7c2ed5fb0556..8a37551132d6 100644
--- a/src/libimaevm.c
+++ b/src/libimaevm.c
@@ -534,11 +534,21 @@ int calc_hash_sigv3(enum evm_ima_xattr_type type, const char *algo,
 		return -EINVAL;
 	}
 
-	if ((hash_algo = imaevm_get_hash_algo(algo)) < 0) {
-		log_err("Hash algorithm %s not supported\n", algo);
-		return -EINVAL;
+	/*
+	 * Calculating the hash is based on the fsverity hash algorithm,
+	 * while verifying the signature is based on the hash algorithm
+	 * contained in the signature header.
+	 */
+	if (algo) {
+		if ((hash_algo = imaevm_get_hash_algo(algo)) < 0) {
+			log_err("Hash algorithm %s not supported\n", algo);
+			return -EINVAL;
+		}
+		file_id.hash_algorithm = hash_algo;
+	} else {
+		algo = imaevm_params.hash_algo;
+		file_id.hash_algorithm = imaevm_get_hash_algo(algo);
 	}
-	file_id.hash_algorithm = hash_algo;
 
 	md = EVP_get_digestbyname(algo);
 	if (!md) {
@@ -622,7 +632,7 @@ int imaevm_hash_algo_from_sig(unsigned char *sig)
 		default:
 			return -1;
 		}
-	} else if (sig[0] == DIGSIG_VERSION_2) {
+	} else if (sig[0] == DIGSIG_VERSION_2 || sig[0] == DIGSIG_VERSION_3) {
 		hashalgo = ((struct signature_v2_hdr *)sig)->hash_algo;
 		if (hashalgo >= PKEY_HASH__LAST)
 			return -1;
@@ -634,8 +644,11 @@ int imaevm_hash_algo_from_sig(unsigned char *sig)
 int verify_hash(const char *file, const unsigned char *hash, int size, unsigned char *sig,
 		int siglen)
 {
+	unsigned char sigv3_hash[MAX_DIGEST_SIZE];
+	int ret;
+
 	/* Get signature type from sig header */
-	if (sig[0] == DIGSIG_VERSION_1) {
+	if (sig[1] == DIGSIG_VERSION_1) {
 		const char *key = NULL;
 
 		/* Read pubkey from RSA key */
@@ -643,9 +656,17 @@ int verify_hash(const char *file, const unsigned char *hash, int size, unsigned
 			key = "/etc/keys/pubkey_evm.pem";
 		else
 			key = imaevm_params.keyfile;
-		return verify_hash_v1(file, hash, size, sig, siglen, key);
-	} else if (sig[0] == DIGSIG_VERSION_2) {
-		return verify_hash_v2(file, hash, size, sig, siglen);
+		return verify_hash_v1(file, hash, size, sig + 1, siglen - 1,
+				      key);
+	} else if (sig[1] == DIGSIG_VERSION_2) {
+		return verify_hash_v2(file, hash, size, sig + 1, siglen - 1);
+	} else if (sig[1] == DIGSIG_VERSION_3) {
+		ret = calc_hash_sigv3(sig[0], NULL, hash, sigv3_hash);
+		if (ret < 0)
+			return ret;
+
+		return verify_hash_v2(file, sigv3_hash, size, sig + 1,
+				      siglen - 1);
 	} else
 		return -1;
 }
@@ -656,11 +677,16 @@ int ima_verify_signature(const char *file, unsigned char *sig, int siglen,
 	unsigned char hash[MAX_DIGEST_SIZE];
 	int hashlen, sig_hash_algo;
 
-	if (sig[0] != EVM_IMA_XATTR_DIGSIG) {
+	if ((sig[0] != EVM_IMA_XATTR_DIGSIG) && (sig[0] != IMA_VERITY_DIGSIG)) {
 		log_err("%s: xattr ima has no signature\n", file);
 		return -1;
 	}
 
+	if (!digest && sig[0] == IMA_VERITY_DIGSIG) {
+		log_err("%s: calculating the fs-verity digest is not supported\n", file);
+		return -1;
+	}
+
 	sig_hash_algo = imaevm_hash_algo_from_sig(sig + 1);
 	if (sig_hash_algo < 0) {
 		log_err("%s: Invalid signature\n", file);
@@ -674,14 +700,14 @@ int ima_verify_signature(const char *file, unsigned char *sig, int siglen,
 	 * measurement list, not by calculating the local file digest.
 	 */
 	if (digestlen > 0)
-	    return verify_hash(file, digest, digestlen, sig + 1, siglen - 1);
+		return verify_hash(file, digest, digestlen, sig, siglen);
 
 	hashlen = ima_calc_hash(file, hash);
 	if (hashlen <= 1)
 		return hashlen;
 	assert(hashlen <= sizeof(hash));
 
-	return verify_hash(file, hash, hashlen, sig + 1, siglen - 1);
+	return verify_hash(file, hash, hashlen, sig, siglen);
 }
 
 /*
-- 
2.27.0

Re: [PATCH v2 ima-evm-utils 1/3] initialize errno in cmd_sign_hash()

[Stefan Berger]

On 5/12/22 14:30, Mimi Zohar wrote:
> Prevent "errno: No such file or directory (2)" message.

I guess there's an error being returned from call_command() but this 
errno is unrelated or confusing. Maybe errno should be initialized at 
the beginning of main() or beginning of call_command() to clear it 
before any command is run that can return an error and where the errno 
may be confusing the user otherwise.

> 
> Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
> ---
>   src/evmctl.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/src/evmctl.c b/src/evmctl.c
> index 8bdd34817408..ca9449498321 100644
> --- a/src/evmctl.c
> +++ b/src/evmctl.c
> @@ -737,6 +737,7 @@ static int cmd_sign_hash(struct command *cmd)
>   	unsigned char sig[MAX_SIGNATURE_SIZE] = "\x03";
>   	int siglen;
>   
> +	errno = 0;
>   	key = imaevm_params.keyfile ? : "/etc/keys/privkey_evm.pem";
>   
>   	/* support reading hash (eg. output of shasum) */

Re: [PATCH v2 ima-evm-utils 2/3] Sign an fs-verity file digest

[Stefan Berger]

On 5/12/22 14:30, Mimi Zohar wrote:
> Sign fs-verity file digests provided in the format as produced by
> "fsverity measure".  The output is of the same format as the input,
> but with the file signature appended.  Use setfattr to write the
> signature as security.ima xattr.
> 
> fsverity measure format: <algo>:<hash> <pathname>
> output format: <algo>:<hash> <pathname> <signature>
> 
> Instead of directly signing the fsverity hash, to disambiguate the
> original IMA signatures from the fs-verity signatures stored in the
> security.ima xattr a new signature format version 3 (sigv3) was
> defined as the hash of the xattr type (enum evm_ima_xattr_type),
> the hash algorithm (enum hash_algo), and the hash.
> 
> Example:
> fsverity measure <pathname> | evmctl sign_hash --veritysig \
>   --key <pem encoded private key>
> 
> Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
> ---
>   README          |   3 +-
>   src/evmctl.c    | 103 +++++++++++++++++++++++++++++++++++++++++-------
>   src/imaevm.h    |   5 ++-
>   src/libimaevm.c |  85 +++++++++++++++++++++++++++++++++++++++
>   4 files changed, 179 insertions(+), 17 deletions(-)
> 
> diff --git a/README b/README
> index 5b5ecb52a74b..ffe46ad75728 100644
> --- a/README
> +++ b/README
> @@ -34,7 +34,7 @@ COMMANDS
>    ima_hash file
>    ima_measurement [--ignore-violations] [--verify-sig [--key "key1, key2, ..."]]  [--pcrs [hash-algorithm,]file [--pcrs hash-algorithm,file] ...] file
>    ima_fix [-t fdsxm] path
> - sign_hash [--key key] [--pass password]
> + sign_hash [--veritysig] [--key key] [--pass password]
>    hmac [--imahash | --imasig ] file
>   
>   
> @@ -43,6 +43,7 @@ OPTIONS
>   
>     -a, --hashalgo     sha1, sha224, sha256, sha384, sha512
>     -s, --imasig       make IMA signature
> +      --veritysig    sign an fs-verity file digest hash
>     -d, --imahash      make IMA hash
>     -f, --sigfile      store IMA signature in .sig file instead of xattr
>         --xattr-user   store xattrs in user namespace (for testing purposes)
> diff --git a/src/evmctl.c b/src/evmctl.c
> index ca9449498321..9152b0a5c7c2 100644
> --- a/src/evmctl.c
> +++ b/src/evmctl.c
> @@ -135,6 +135,7 @@ static int msize;
>   static dev_t fs_dev;
>   static bool evm_immutable;
>   static bool evm_portable;
> +static bool veritysig;
>   
>   #define HMAC_FLAG_NO_UUID	0x0001
>   #define HMAC_FLAG_CAPS_SET	0x0002
> @@ -726,34 +727,102 @@ static int cmd_sign_ima(struct command *cmd)
>   	return do_cmd(cmd, sign_ima_file);
>   }
>   
> +/*
> + * Sign file hash(es) provided in the format as produced by either
> + * sha*sum or "fsverity measure".
> + *
> + * sha*sum format: <hash> <pathname>
> + * fsverity measure format: <algo>:<hash> <pathname>
> + *
> + * To disambiguate the resulting file signatures, a new signature format
> + * version 3 (sigv3) was defined as the hash of the xattr type (enum
> + * evm_ima_xattr_type), the hash algorithm (enum hash_algo), and the hash.
> + *
> + * Either directly sign the sha*sum hash or indirectly sign the fsverity
> + * hash (sigv3).
> + *
> + * The output is the same format as the input with the resulting file
> + * signature appended.
> + */
>   static int cmd_sign_hash(struct command *cmd)
>   {
> +	unsigned char sigv3_hash[MAX_DIGEST_SIZE];
> +	unsigned char sig[MAX_SIGNATURE_SIZE];
> +	unsigned char hash[MAX_DIGEST_SIZE];
> +	int siglen, algolen, hashlen = 0;
> +	char *line = NULL, *token, *hashp;
> +	size_t line_len = 0;
>   	const char *key;
> -	char *token, *line = NULL;
> -	int hashlen = 0;
> -	size_t line_len;
> +	char algo[12];
>   	ssize_t len;
> -	unsigned char hash[MAX_DIGEST_SIZE];
> -	unsigned char sig[MAX_SIGNATURE_SIZE] = "\x03";
> -	int siglen;
> +	int ret;
>   
>   	errno = 0;
>   	key = imaevm_params.keyfile ? : "/etc/keys/privkey_evm.pem";
>   
> -	/* support reading hash (eg. output of shasum) */
>   	while ((len = getline(&line, &line_len, stdin)) > 0) {
>   		/* remove end of line */
>   		if (line[len - 1] == '\n')
>   			line[--len] = '\0';
>   
> -		/* find the end of the hash */
> -		token = strpbrk(line, ", \t");
> -		hashlen = token ? token - line : strlen(line);
> +		/*
> +		 * Before either directly or indirectly signing the hash,
> +		 * convert the hex-ascii hash representation to binary.
> +		 */
> +		if (veritysig) {
> +
> +			/* split the algorithm from the hash */
> +			hashp = strpbrk(line, ":");
> +			if (!hashp) {	/* pointer to the delimiter */
> +				log_err("Missing fsverity hash algorithm\n");
> +				continue;
> +			}
> +
> +			algolen = hashp - line;
> +			if (algolen > sizeof(algo))
> +				algolen = sizeof(algo);

I think a hash name exceeding the max buffer size and needing to be 
truncating it should be an error since the name to index conversion will 
fail  later on.


> +			if (algolen <= 0) {
> +				log_err("Missing fsverity hash algorithm\n");
> +				continue;
> +			}
> +
> +			strncpy(algo, line, algolen);
> +			algo[algolen] = 0;	/* Nul terminate algorithm */

per above: if algolen == sizeof(algo) then you have an out-of-bounds 
access here...

Re: [PATCH v2 ima-evm-utils 1/3] initialize errno in cmd_sign_hash()

[Mimi Zohar]

On Thu, 2022-05-12 at 15:14 -0400, Stefan Berger wrote:
> 
> On 5/12/22 14:30, Mimi Zohar wrote:
> > Prevent "errno: No such file or directory (2)" message.
> 
> I guess there's an error being returned from call_command() but this 
> errno is unrelated or confusing. Maybe errno should be initialized at 
> the beginning of main() or beginning of call_command() to clear it 
> before any command is run that can return an error and where the errno 
> may be confusing the user otherwise.

'errno' is being set on failure to open/fopen and access() in
file_exist(). 

thanks,

Mimi

Re: [PATCH v2 ima-evm-utils 2/3] Sign an fs-verity file digest

[Mimi Zohar]

On Thu, 2022-05-12 at 17:48 -0400, Stefan Berger wrote:
> > -             /* find the end of the hash */
> > -             token = strpbrk(line, ", \t");
> > -             hashlen = token ? token - line : strlen(line);
> > +             /*
> > +              * Before either directly or indirectly signing the hash,
> > +              * convert the hex-ascii hash representation to binary.
> > +              */
> > +             if (veritysig) {
> > +
> > +                     /* split the algorithm from the hash */
> > +                     hashp = strpbrk(line, ":");
> > +                     if (!hashp) {   /* pointer to the delimiter */
> > +                             log_err("Missing fsverity hash algorithm\n");
> > +                             continue;
> > +                     }
> > +
> > +                     algolen = hashp - line;
> > +                     if (algolen > sizeof(algo))
> > +                             algolen = sizeof(algo);
> 
> I think a hash name exceeding the max buffer size and needing to be 
> truncating it should be an error since the name to index conversion will 
> fail  later on.

Sure.  In fact, the hash algorithm name size should be limited to the
maximum size of those algorithms that fs-verity actually supports.

thanks,

Mimi

Re: [PATCH v2 ima-evm-utils 3/3] Verify an fs-verity file digest based signature

[Stefan Berger]

On 5/12/22 14:30, Mimi Zohar wrote:
> ima-evm-utils does not attempt to calculate or even read the fs-verity
> file hash, but can verify the fs-verity signature based on the fsverity
> file hash, both contained in the measurement list record.
> 
> For the time being only fs-verity supports signature format v3 (sigv3).
> To differentiate between the existing IMA and fs-verity file signatures,
> modify the verify_hash() 'sig' argument to be a pointer to the entire
> xattr, including the xattr type.
> 
> Example:
> evmctl ima_measurement --key <DER encoded public key> \
>   --verify-sig /sys/kernel/security/ima/binary_runtime_measurements
> 
> Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
> ---
>   src/evmctl.c    | 11 +++++++++--
>   src/libimaevm.c | 50 +++++++++++++++++++++++++++++++++++++------------
>   2 files changed, 47 insertions(+), 14 deletions(-)
> 
> diff --git a/src/evmctl.c b/src/evmctl.c
> index 9152b0a5c7c2..593eed80f96a 100644
> --- a/src/evmctl.c
> +++ b/src/evmctl.c
> @@ -909,7 +909,7 @@ static int verify_evm(const char *file)
>   		return mdlen;
>   	assert(mdlen <= sizeof(hash));
>   
> -	return verify_hash(file, hash, mdlen, sig + 1, len - 1);
> +	return verify_hash(file, hash, mdlen, sig, len);
>   }
>   
>   static int cmd_verify_evm(struct command *cmd)
> @@ -1572,7 +1572,8 @@ void ima_ng_show(struct template_entry *entry)
>   	fieldp += field_len;
>   	total_len -= field_len;
>   
> -	if (!strcmp(entry->name, "ima-sig")) {
> +	if (!strcmp(entry->name, "ima-sig") ||
> +	    !strcmp(entry->name, "ima-sigv2")) {
>   		/* get signature */
>   		field_len = *(uint32_t *)fieldp;
>   		fieldp += sizeof(field_len);
> @@ -1618,11 +1619,17 @@ void ima_ng_show(struct template_entry *entry)
>   			log_info(" ");
>   			log_dump(sig, sig_len);
>   		}
> +
> +		/*
> +		 * Either verify the signature against the hash contained in
> +		 * the measurement list or calculate the hash.
> +		 */
>   		if (verify_list_sig)
>   			err = ima_verify_signature(path, sig, sig_len,
>   						   digest, digest_len);
>   		else
>   			err = ima_verify_signature(path, sig, sig_len, NULL, 0);
> +
>   		if (!err && imaevm_params.verbose > LOG_INFO)
>   			log_info("%s: verification is OK\n", path);
>   	} else {
> diff --git a/src/libimaevm.c b/src/libimaevm.c
> index 7c2ed5fb0556..8a37551132d6 100644
> --- a/src/libimaevm.c
> +++ b/src/libimaevm.c
> @@ -534,11 +534,21 @@ int calc_hash_sigv3(enum evm_ima_xattr_type type, const char *algo,
>   		return -EINVAL;
>   	}
>   
> -	if ((hash_algo = imaevm_get_hash_algo(algo)) < 0) {
> -		log_err("Hash algorithm %s not supported\n", algo);
> -		return -EINVAL;
> +	/*
> +	 * Calculating the hash is based on the fsverity hash algorithm,
> +	 * while verifying the signature is based on the hash algorithm
> +	 * contained in the signature header.
> +	 */
> +	if (algo) {
> +		if ((hash_algo = imaevm_get_hash_algo(algo)) < 0) {
> +			log_err("Hash algorithm %s not supported\n", algo);
> +			return -EINVAL;
> +		}
> +		file_id.hash_algorithm = hash_algo;
> +	} else {
> +		algo = imaevm_params.hash_algo;
> +		file_id.hash_algorithm = imaevm_get_hash_algo(algo);

You should probably compare this also against '< 0' as it was before. If 
you do it outside the if-else the two cases can share this:

	if (!algo)
		algo = imaevm_params.hash_algo;

	if ((hash_algo = imaevm_get_hash_algo(algo)) < 0) {
		log_err("Hash algorithm %s not supported\n", algo);
		return -EINVAL;
	}
	file_id.hash_algorithm = hash_algo;

Re: [PATCH v2 ima-evm-utils 2/3] Sign an fs-verity file digest

[Eric Biggers]

On Thu, May 12, 2022 at 02:30:55PM -0400, Mimi Zohar wrote:
> Sign fs-verity file digests provided in the format as produced by
> "fsverity measure".

This is correct, but it probably would be more useful to give "fsverity digest"
as the example, since "fsverity digest" doesn't depend on the file already
having verity enabled.

- Eric