ima: permit fsverity's file digests in the IMA measurement list

Permit fsverity's file digest (a hash of struct fsverity_descriptor) to
be included in the IMA measurement list, based on the new measurement
policy rule 'digest_type=verity' option.

To differentiate between a regular IMA file hash from an fsverity's
file digest, use the new d-ngv2 format field included in the ima-ngv2
template.

The following policy rule requires fsverity file digests and specifies
the new 'ima-ngv2' template, which contains the new 'd-ngv2' field. The
policy rule may be constrained, for example based on a fsuuid or LSM
label.

measure func=FILE_CHECK digest_type=verity template=ima-ngv2

Acked-by: Stefan Berger <[e-mail]>
Signed-off-by: Mimi Zohar <[e-mail]>

Documentation/ABI/testing/ima_policy

···
 				[fowner=] [fgroup=]]
 			lsm:	[[subj_user=] [subj_role=] [subj_type=]
 				 [obj_user=] [obj_role=] [obj_type=]]
-			option:	[[appraise_type=]] [template=] [permit_directio]
-				[appraise_flag=] [appraise_algos=] [keyrings=]
+			option:	[digest_type=] [template=] [permit_directio]
+				[appraise_type=] [appraise_flag=]
+				[appraise_algos=] [keyrings=]
 		  base:
 			func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK]
 				[FIRMWARE_CHECK]
···
 			appraise_flag:= [check_blacklist]
 			Currently, blacklist check is only for files signed with appended
 			signature.
+			digest_type:= verity
+			    Require fs-verity's file digest instead of the
+			    regular IMA file hash.
 			keyrings:= list of keyrings
 			(eg, .builtin_trusted_keys|.ima). Only valid
 			when action is "measure" and func is KEY_CHECK.
···
 		security.ima xattr of a file:
 
 			appraise func=SETXATTR_CHECK appraise_algos=sha256,sha384,sha512
+
+		Example of a 'measure' rule requiring fs-verity's digests
+		with indication of type of digest in the measurement list.
+
+			measure func=FILE_CHECK digest_type=verity \
+				template=ima-ngv2

Documentation/security/IMA-templates.rst

···
  - 'n': the name of the event (i.e. the file name), with size up to 255 bytes;
  - 'd-ng': the digest of the event, calculated with an arbitrary hash
    algorithm (field format: <hash algo>:digest);
- - 'd-ngv2': same as d-ng, but prefixed with the "ima" digest type
+ - 'd-ngv2': same as d-ng, but prefixed with the "ima" or "verity" digest type
    (field format: <digest type>:<hash algo>:digest);
  - 'd-modsig': the digest of the event without the appended modsig;
  - 'n-ng': the name of the event, without size limitations;

security/integrity/ima/ima_api.c

···
 #include <linux/xattr.h>
 #include <linux/evm.h>
 #include <linux/iversion.h>
+#include <linux/fsverity.h>
 
 #include "ima.h"
 
···
 				allowed_algos);
 }
 
+static int ima_get_verity_digest(struct integrity_iint_cache *iint,
+				 struct ima_max_digest_data *hash)
+{
+	enum hash_algo verity_alg;
+	int ret;
+
+	/*
+	 * On failure, 'measure' policy rules will result in a file data
+	 * hash containing 0's.
+	 */
+	ret = fsverity_get_digest(iint->inode, hash->digest, &verity_alg);
+	if (ret)
+		return ret;
+
+	/*
+	 * Unlike in the case of actually calculating the file hash, in
+	 * the fsverity case regardless of the hash algorithm, return
+	 * the verity digest to be included in the measurement list. A
+	 * mismatch between the verity algorithm and the xattr signature
+	 * algorithm, if one exists, will be detected later.
+	 */
+	hash->hdr.algo = verity_alg;
+	hash->hdr.length = hash_digest_size[verity_alg];
+	return 0;
+}
+
 /*
  * ima_collect_measurement - collect file measurement
  *
···
 	 */
 	i_version = inode_query_iversion(inode);
 	hash.hdr.algo = algo;
+	hash.hdr.length = hash_digest_size[algo];
 
 	/* Initialize hash digest to 0's in case of failure */
 	memset(&hash.digest, 0, sizeof(hash.digest));
 
-	if (buf)
+	if (iint->flags & IMA_VERITY_REQUIRED) {
+		result = ima_get_verity_digest(iint, &hash);
+		switch (result) {
+		case 0:
+			break;
+		case -ENODATA:
+			audit_cause = "no-verity-digest";
+			break;
+		default:
+			audit_cause = "invalid-verity-digest";
+			break;
+		}
+	} else if (buf) {
 		result = ima_calc_buffer_hash(buf, size, &hash.hdr);
-	else
+	} else {
 		result = ima_calc_file_hash(file, &hash.hdr);
+	}
 
-	if (result && result != -EBADF && result != -EINVAL)
+	if (result == -ENOMEM)
 		goto out;
 
 	length = sizeof(hash.hdr) + hash.hdr.length;

security/integrity/ima/ima_main.c

···
 	hash_algo = ima_get_hash_algo(xattr_value, xattr_len);
 
 	rc = ima_collect_measurement(iint, file, buf, size, hash_algo, modsig);
-	if (rc != 0 && rc != -EBADF && rc != -EINVAL)
+	if (rc == -ENOMEM)
 		goto out_locked;
 
 	if (!pathbuf)	/* ima_rdwr_violation possibly pre-fetched */

security/integrity/ima/ima_policy.c

···
 	Opt_fowner_gt, Opt_fgroup_gt,
 	Opt_uid_lt, Opt_euid_lt, Opt_gid_lt, Opt_egid_lt,
 	Opt_fowner_lt, Opt_fgroup_lt,
+	Opt_digest_type,
 	Opt_appraise_type, Opt_appraise_flag, Opt_appraise_algos,
 	Opt_permit_directio, Opt_pcr, Opt_template, Opt_keyrings,
 	Opt_label, Opt_err
···
 	{Opt_egid_lt, "egid<%s"},
 	{Opt_fowner_lt, "fowner<%s"},
 	{Opt_fgroup_lt, "fgroup<%s"},
+	{Opt_digest_type, "digest_type=%s"},
 	{Opt_appraise_type, "appraise_type=%s"},
 	{Opt_appraise_flag, "appraise_flag=%s"},
 	{Opt_appraise_algos, "appraise_algos=%s"},
···
 #undef MSG
 }
 
+/*
+ * Warn if the template does not contain the given field.
+ */
+static void check_template_field(const struct ima_template_desc *template,
+				 const char *field, const char *msg)
+{
+	int i;
+
+	for (i = 0; i < template->num_fields; i++)
+		if (!strcmp(template->fields[i]->field_id, field))
+			return;
+
+	pr_notice_once("%s", msg);
+}
+
 static bool ima_validate_rule(struct ima_rule_entry *entry)
 {
 	/* Ensure that the action is set and is compatible with the flags */
···
 				     IMA_INMASK | IMA_EUID | IMA_PCR |
 				     IMA_FSNAME | IMA_GID | IMA_EGID |
 				     IMA_FGROUP | IMA_DIGSIG_REQUIRED |
-				     IMA_PERMIT_DIRECTIO | IMA_VALIDATE_ALGOS))
+				     IMA_PERMIT_DIRECTIO | IMA_VALIDATE_ALGOS |
+				     IMA_VERITY_REQUIRED))
 			return false;
 
 		break;
···
 						   LSM_SUBJ_TYPE,
 						   AUDIT_SUBJ_TYPE);
 			break;
+		case Opt_digest_type:
+			ima_log_string(ab, "digest_type", args[0].from);
+			if ((strcmp(args[0].from, "verity")) == 0)
+				entry->flags |= IMA_VERITY_REQUIRED;
+			else
+				result = -EINVAL;
+			break;
 		case Opt_appraise_type:
 			ima_log_string(ab, "appraise_type", args[0].from);
 			if ((strcmp(args[0].from, "imasig")) == 0)
···
 		template_desc = entry->template ? entry->template :
 						  ima_template_desc_current();
 		check_template_modsig(template_desc);
+	}
+
+	/* d-ngv2 template field recommended for unsigned fs-verity digests */
+	if (!result && entry->action == MEASURE &&
+	    entry->flags & IMA_VERITY_REQUIRED) {
+		template_desc = entry->template ? entry->template :
+						  ima_template_desc_current();
+		check_template_field(template_desc, "d-ngv2",
+				     "verity rules should include d-ngv2");
 	}
 
 	audit_log_format(ab, "res=%d", !result);
···
 		else
 			seq_puts(m, "appraise_type=imasig ");
 	}
+	if (entry->flags & IMA_VERITY_REQUIRED)
+		seq_puts(m, "digest_type=verity ");
 	if (entry->flags & IMA_CHECK_BLACKLIST)
 		seq_puts(m, "appraise_flag=check_blacklist ");
 	if (entry->flags & IMA_PERMIT_DIRECTIO)

security/integrity/ima/ima_template_lib.c

···
 
 enum digest_type {
 	DIGEST_TYPE_IMA,
+	DIGEST_TYPE_VERITY,
 	DIGEST_TYPE__LAST
 };
 
-#define DIGEST_TYPE_NAME_LEN_MAX 4	/* including NUL */
+#define DIGEST_TYPE_NAME_LEN_MAX 7	/* including NUL */
 static const char * const digest_type_name[DIGEST_TYPE__LAST] = {
-	[DIGEST_TYPE_IMA] = "ima"
+	[DIGEST_TYPE_IMA] = "ima",
+	[DIGEST_TYPE_VERITY] = "verity"
 };
 
 static int ima_write_template_field_data(const void *data, const u32 datalen,
···
 	 *
 	 *    where 'DATA_FMT_DIGEST' is the original digest format ('d')
 	 *      with a hash size limitation of 20 bytes,
-	 *    where <digest type> is "ima",
+	 *    where <digest type> is either "ima" or "verity",
 	 *    where <hash algo> is the hash_algo_name[] string.
 	 */
 	u8 buffer[DIGEST_TYPE_NAME_LEN_MAX + CRYPTO_MAX_ALG_NAME + 2 +
···
 	cur_digestsize = event_data->iint->ima_hash->length;
 
 	hash_algo = event_data->iint->ima_hash->algo;
+	if (event_data->iint->flags & IMA_VERITY_REQUIRED)
+		digest_type = DIGEST_TYPE_VERITY;
 out:
 	return ima_eventdigest_init_common(cur_digest, cur_digestsize,
 					   digest_type, hash_algo,

security/integrity/integrity.h

···
 #define IMA_FAIL_UNVERIFIABLE_SIGS	0x10000000
 #define IMA_MODSIG_ALLOWED	0x20000000
 #define IMA_CHECK_BLACKLIST	0x40000000
+#define IMA_VERITY_REQUIRED	0x80000000
 
 #define IMA_DO_MASK		(IMA_MEASURE | IMA_APPRAISE | IMA_AUDIT | \
 				 IMA_HASH | IMA_APPRAISE_SUBMASK)