Re: [PATCH v24 04/25] IMA: avoid label collisions with stacked LSMs
From: Mimi Zohar <zohar@linux.ibm.com>
Date: 2021-02-14 18:23:05
Also in:
lkml, selinux
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.)
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Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> To: Mimi Zohar <zohar@linux.ibm.com> To: linux-integrity@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.
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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=4diff --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];
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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".
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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