[PATCH v24 04/25] IMA: avoid label collisions with stacked LSMs

Casey Schaufler
2021-01-26T18:11:41Z

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.

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=]]
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];
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;
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);
+
static struct ima_rule_opt_list *ima_alloc_rule_opt_list(const substring_t *src)
{
struct ima_rule_opt_list *opt_list;
@@ -346,7 +359,8 @@ static void ima_lsm_free_rule(struct ima_rule_entry *entry)

for (i = 0; i < MAX_LSM_RULES; i++) {
for (r = 0; r < LSMBLOB_ENTRIES; r++)
- ima_filter_rule_free(entry->lsm[i].rules[r]);
+ if (entry->lsm[i].rules[r])
+ ima_filter_rule_free(entry->lsm[i].rules[r]);
kfree(entry->lsm[i].args_p);
}
}
@@ -398,7 +412,7 @@ static struct ima_rule_entry *ima_lsm_copy_rule(struct ima_rule_entry *entry)
ima_filter_rule_init(nentry->lsm[i].type, Audit_equal,
nentry->lsm[i].args_p,
&nentry->lsm[i].rules[0]);
- if (!ima_lsm_isset(nentry->lsm[i].rules))
+ if (!ima_lsm_isset(nentry, i))
pr_warn("rule for LSM \'%s\' is undefined\n",
nentry->lsm[i].args_p);
}
@@ -563,7 +577,7 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
int rc = 0;
u32 osid;

- if (!ima_lsm_isset(rule->lsm[i].rules)) {
+ if (!ima_lsm_isset(rule, i)) {
if (!rule->lsm[i].args_p)
continue;
else
@@ -925,6 +939,7 @@ enum {
Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt,
Opt_appraise_type, Opt_appraise_flag,
Opt_permit_directio, Opt_pcr, Opt_template, Opt_keyrings,
+ Opt_lsm,
Opt_err
};

@@ -962,6 +977,7 @@ static const match_table_t policy_tokens = {
{Opt_pcr, "pcr=%s"},
{Opt_template, "template=%s"},
{Opt_keyrings, "keyrings=%s"},
+ {Opt_lsm, "lsm=%s"},
{Opt_err, NULL}
};

@@ -970,7 +986,7 @@ static int ima_lsm_rule_init(struct ima_rule_entry *entry,
{
int result;

- if (ima_lsm_isset(entry->lsm[lsm_rule].rules))
+ if (ima_lsm_isset(entry, lsm_rule))
return -EINVAL;

entry->lsm[lsm_rule].args_p = match_strdup(args);
@@ -981,7 +997,7 @@ static int ima_lsm_rule_init(struct ima_rule_entry *entry,
result = ima_filter_rule_init(entry->lsm[lsm_rule].type, Audit_equal,
entry->lsm[lsm_rule].args_p,
&entry->lsm[lsm_rule].rules[0]);
- if (!ima_lsm_isset(entry->lsm[lsm_rule].rules)) {
+ if (!ima_lsm_isset(entry, lsm_rule)) {
pr_warn("rule for LSM \'%s\' is undefined\n",
entry->lsm[lsm_rule].args_p);

@@ -1488,6 +1504,19 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
&(template_desc->num_fields));
entry->template = template_desc;
break;
+ case Opt_lsm:
+ result = lsm_name_to_slot(args[0].from);
+ if (result == LSMBLOB_INVALID) {
+ int i;
+
+ for (i = 0; i < MAX_LSM_RULES; i++)
+ entry->lsm[i].args_p = NULL;
+ result = -EINVAL;
+ break;
+ }
+ entry->lsm->which_lsm = result;
+ result = 0;
+ break;
case Opt_err:
ima_log_string(ab, "UNKNOWN", p);
result = -EINVAL;
@@ -1524,6 +1553,7 @@ ssize_t ima_parse_add_rule(char *rule)
struct ima_rule_entry *entry;
ssize_t result, len;
int audit_info = 0;
+ int i;

p = strsep(&rule, "\n");
len = strlen(p) + 1;
@@ -1541,6 +1571,9 @@ ssize_t ima_parse_add_rule(char *rule)

INIT_LIST_HEAD(&entry->list);

+ for (i = 0; i < MAX_LSM_RULES; i++)
+ entry->lsm[i].which_lsm = ima_rule_lsm;
+
result = ima_parse_rule(p, entry);
if (result) {
ima_free_rule(entry);
@@ -1751,7 +1784,7 @@ int ima_policy_show(struct seq_file *m, void *v)
}

for (i = 0; i < MAX_LSM_RULES; i++) {
- if (ima_lsm_isset(entry->lsm[i].rules)) {
+ if (ima_lsm_isset(entry, i)) {
switch (i) {
case LSM_OBJ_USER:
seq_printf(m, pt(Opt_obj_user),
@@ -1793,6 +1826,9 @@ int ima_policy_show(struct seq_file *m, void *v)
seq_puts(m, "appraise_flag=check_blacklist ");
if (entry->flags & IMA_PERMIT_DIRECTIO)
seq_puts(m, "permit_directio ");
+ if (entry->lsm->which_lsm >= 0)
+ seq_printf(m, pt(Opt_lsm),
+ lsm_slot_to_name(entry->lsm->which_lsm));
rcu_read_unlock();
seq_puts(m, "\n");
return 0;
--
2.25.4