12:21 p.m.
Hi Casey,
On Tue, 2021-01-26 at 08:40 -0800, Casey Schaufler wrote:
Integrity measurement may filter on security module information
and needs to be clear in the case of multiple active security
modules which applies. Provide a boot option ima_rules_lsm= to
allow the user to specify an active securty module to apply
filters to. If not specified, use the first registered module
that supports the audit_rule_match() LSM hook. Allow the user
to specify in the IMA policy an lsm= option to specify the
security module to use for a particular rule.
Thanks, Casey.
(This patch description line length seems short.)
Signed-off-by: Casey Schaufler <casey(a)schaufler-ca.com>
To: Mimi Zohar <zohar(a)linux.ibm.com>
To: linux-integrity(a)vger.kernel.org
---
Documentation/ABI/testing/ima_policy | 8 +++-
security/integrity/ima/ima_policy.c | 64 ++++++++++++++++++++++------
2 files changed, 57 insertions(+), 15 deletions(-)
diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index e35263f97fc1..a7943d40466f 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -25,7 +25,7 @@ Description:
base: [[func=] [mask=] [fsmagic=] [fsuuid=] [uid=]
[euid=] [fowner=] [fsname=]]
lsm: [[subj_user=] [subj_role=] [subj_type=]
- [obj_user=] [obj_role=] [obj_type=]]
+ [obj_user=] [obj_role=] [obj_type=] [lsm=]]
"[lsm=]" either requires all LSM rules types (e.g. {subj/obj}_user,
role, type) to be exactly the same for multiple LSMs or all of the LSM
rule types are applicable to only a single LSM. Supporting multiple
LSMs with exactly the same LSM labels doesn't seem worth the effort.
Keep it simple - a single rule, containing any LSM rule types, is
applicable to a single LSM.
option: [[appraise_type=]] [template=] [permit_directio]
[appraise_flag=] [keyrings=]
base:
@@ -114,6 +114,12 @@ Description:
measure subj_user=_ func=FILE_CHECK mask=MAY_READ
+ It is possible to explicitly specify which security
+ module a rule applies to using lsm=. If the security
+ modules specified is not active on the system the rule
+ will be rejected. If lsm= is not specified the first
+ security module registered on the system will be assumed.
+
Example of measure rules using alternate PCRs::
measure func=KEXEC_KERNEL_CHECK pcr=4
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 8002683003e6..de72b719c90c 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -82,6 +82,7 @@ struct ima_rule_entry {
void *rules[LSMBLOB_ENTRIES]; /* LSM file metadata specific */
char *args_p; /* audit value */
int type; /* audit type */
+ int which_lsm; /* which of the rules to use */
} lsm[MAX_LSM_RULES];
Even if we wanted to support multiple LSMs within the same rule having
both "rules[LSMBLOB_ENTRIES]" and "which_lsm" shouldn't be
necessary.
The LSMBLOB_ENTRIES should already identify the LSM.
To support a single LSM per policy rule, "which_lsm" should be defined
outside of lsm[MAX_LSM_RULES]. This will simplify the rest of the code
(e.g. matching/freeing rules).
int which_lsm; /* which of the rules to use */
struct {
void *rule; /* LSM file metadata specific */
char *args_p; /* audit value */
int type; /* audit type */
} lsm[MAX_LSM_RULES];
char *fsname;
struct ima_rule_opt_list *keyrings; /* Measure keys added to these keyrings */
@@ -90,17 +91,15 @@ struct ima_rule_entry {
/**
* ima_lsm_isset - Is a rule set for any of the active security modules
- * @rules: The set of IMA rules to check
+ * @entry: the rule entry to examine
+ * @lsm_rule: the specific rule type in question
*
- * If a rule is set for any LSM return true, otherwise return false.
+ * If a rule is set return true, otherwise return false.
*/
-static inline bool ima_lsm_isset(void *rules[])
+static inline bool ima_lsm_isset(struct ima_rule_entry *entry, int lsm_rule)
{
- int i;
-
- for (i = 0; i < LSMBLOB_ENTRIES; i++)
- if (rules[i])
- return true;
+ if (entry->lsm[lsm_rule].rules[entry->lsm[lsm_rule].which_lsm])
+ return true;
If each IMA policy rule is limited to a specific LSM, then the test
would be "entry->which_lsm".
return false;
}
@@ -273,6 +272,20 @@ static int __init default_appraise_policy_setup(char *str)
}
__setup("ima_appraise_tcb", default_appraise_policy_setup);
+static int ima_rule_lsm __ro_after_init;
+
+static int __init ima_rule_lsm_init(char *str)
+{
+ ima_rule_lsm = lsm_name_to_slot(str);
+ if (ima_rule_lsm < 0) {
+ ima_rule_lsm = 0;
+ pr_err("rule lsm \"%s\" not registered", str);
+ }
+
+ return 1;
+}
+__setup("ima_rule_lsm=", ima_rule_lsm_init);
The patch description refers to "ima_rules_lsm=". Please update one or
the other.
thanks,
Mimi