[RFC][PATCH 5/6] ima: added ima_template and ima_template_fmt new policy options

[Roberto Sassu]

This patch adds the support for 'ima_template' and 'ima_template_fmt'
policy options. They allow to define which template and, thus, which
information should be included in measurements entries generated from
events that match other rules' criteria.

With this feature, it is possible to include for each measurement entry
only relevant information. For example, while measurements that report
the execution of the execve() system call may contain the credentials
being installed on the current process (stored in the 'cred' field of the
'linux_binprm' structure), others should not include it (also because
the pointer to the above structure is not available from other IMA hooks).

A sample policy to produce measurements the way is described above may be:

---
measure func=BPRM_CHECK mask=MAY_EXEC ima_template_fmt=d-ng|n-ng|bprm-type
measure func=FILE_MMAP mask=MAY_EXEC
---

where 'bprm-type' is the identifier of a field (whose code is not yet
upstreamed) which displays the type part of a LSM label from credentials
stored in the 'linux_binprm' structure.

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxx>
---
 Documentation/ABI/testing/ima_policy     |  6 ++++-
 Documentation/security/IMA-templates.txt | 19 ++++++++------
 security/integrity/ima/ima_policy.c      | 45 +++++++++++++++++++++++++++++++-
 3 files changed, 60 insertions(+), 10 deletions(-)

diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index f1c5cc9..7fbe47d 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -23,7 +23,7 @@ Description:
 				 [fowner]]
 			lsm:	[[subj_user=] [subj_role=] [subj_type=]
 				 [obj_user=] [obj_role=] [obj_type=]]
-			option:	[[appraise_type=]]
+			option:	[[appraise_type=] [ima_template=] [ima_template_fmt=]]
 
 		base: 	func:= [BPRM_CHECK][MMAP_CHECK][FILE_CHECK][MODULE_CHECK]
 			mask:= [MAY_READ] [MAY_WRITE] [MAY_APPEND] [MAY_EXEC]
@@ -33,6 +33,10 @@ Description:
 			fowner:=decimal value
 		lsm:  	are LSM specific
 		option:	appraise_type:= [imasig]
+			ima_template:= an already defined template
+			ima_template_fmt:= a custom template format
+					   (see Documentation/security/IMA-templates.txt
+					   for more details)
 
 		default policy:
 			# PROC_SUPER_MAGIC
diff --git a/Documentation/security/IMA-templates.txt b/Documentation/security/IMA-templates.txt
index 08ea2da..61d9f0d 100644
--- a/Documentation/security/IMA-templates.txt
+++ b/Documentation/security/IMA-templates.txt
@@ -36,13 +36,14 @@ from the set of the supported ones.
 After the initialization step, IMA will call ima_alloc_init_template()
 (new function defined within the patches for the new template management
 mechanism) to generate a new measurement entry by using the template
-descriptor chosen through the kernel configuration or through the newly
-introduced 'ima_template' and 'ima_template_fmt' kernel command line parameters.
-It is during this phase that the advantages of the new architecture are
-clearly shown: the latter function will not contain specific code to handle
-a given template but, instead, it simply calls the init() method of the template
-fields associated to the chosen template descriptor and store the result
-(pointer to allocated data and data length) in the measurement entry structure.
+descriptor chosen through the kernel configuration, the newly introduced
+'ima_template' and 'ima_template_fmt' kernel command line parameters and
+new policy options with the same names. It is during this phase that the
+advantages of the new architecture are clearly shown: the latter function
+will not contain specific code to handle a given template but, instead, it
+simply calls the init() method of the template fields associated to the
+chosen template descriptor and store the result (pointer to allocated data
+and data length) in the measurement entry structure.
 
 The same mechanism is employed to display measurements entries.
 The functions ima[_ascii]_measurements_show() retrieve, for each entry,
@@ -83,4 +84,6 @@ currently the following methods are supported:
  - specify a template descriptor name from the kernel command line through
    the 'ima_template=' parameter;
  - register a new template descriptor with custom format through the kernel
-   command line parameter 'ima_template_fmt='.
+   command line parameter 'ima_template_fmt=';
+ - provide desired template name or custom format for specific events through
+   the new policy options 'ima_template=' and 'ima_template_fmt='.
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index a9c3d3c..df852ec 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -50,6 +50,8 @@ struct ima_rule_entry {
 	u8 fsuuid[16];
 	kuid_t uid;
 	kuid_t fowner;
+	char *template_name;
+	char *template_fmt;
 	struct {
 		void *rule;	/* LSM file metadata specific */
 		void *args_p;	/* audit value */
@@ -351,7 +353,8 @@ enum {
 	Opt_obj_user, Opt_obj_role, Opt_obj_type,
 	Opt_subj_user, Opt_subj_role, Opt_subj_type,
 	Opt_func, Opt_mask, Opt_fsmagic, Opt_uid, Opt_fowner,
-	Opt_appraise_type, Opt_fsuuid
+	Opt_appraise_type, Opt_fsuuid,
+	Opt_ima_template, Opt_ima_template_fmt
 };
 
 static match_table_t policy_tokens = {
@@ -373,6 +376,8 @@ static match_table_t policy_tokens = {
 	{Opt_uid, "uid=%s"},
 	{Opt_fowner, "fowner=%s"},
 	{Opt_appraise_type, "appraise_type=%s"},
+	{Opt_ima_template, "ima_template=%s"},
+	{Opt_ima_template_fmt, "ima_template_fmt=%s"},
 	{Opt_err, NULL}
 };
 
@@ -421,6 +426,7 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 	entry->action = UNKNOWN;
 	while ((p = strsep(&rule, " \t")) != NULL) {
 		substring_t args[MAX_OPT_ARGS];
+		struct ima_template_desc *desc;
 		int token;
 		unsigned long lnum;
 
@@ -621,6 +627,43 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 			else
 				result = -EINVAL;
 			break;
+		case Opt_ima_template:
+			ima_log_string(ab, "ima_template", args[0].from);
+
+			if (entry->template_name || entry->template_fmt) {
+				result = -EINVAL;
+				break;
+			}
+
+			desc = ima_get_template_desc(args[0].from, NULL);
+			if (strcmp(desc->name, args[0].from) != 0) {
+				result = -EINVAL;
+				break;
+			}
+
+			entry->template_name = kstrdup(args[0].from,
+						       GFP_KERNEL);
+			if (!entry->template_name)
+				result = -EINVAL;
+			break;
+		case Opt_ima_template_fmt:
+			ima_log_string(ab, "ima_template_fmt", args[0].from);
+
+			if (entry->template_fmt || entry->template_name) {
+				result = -EINVAL;
+				break;
+			}
+
+			desc = ima_get_template_desc(NULL, args[0].from);
+			if (strcmp(desc->fmt, args[0].from) != 0) {
+				result = -EINVAL;
+				break;
+			}
+
+			entry->template_fmt = kstrdup(args[0].from, GFP_KERNEL);
+			if (!entry->template_fmt)
+				result = -EINVAL;
+			break;
 		case Opt_err:
 			ima_log_string(ab, "UNKNOWN", p);
 			result = -EINVAL;
-- 
1.8.1.4

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