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Diffstat (limited to 'security/integrity/ima/ima_policy.c')
-rw-r--r--security/integrity/ima/ima_policy.c174
1 files changed, 158 insertions, 16 deletions
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index fd5d46e511f1..87b9b71cb820 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -35,6 +35,7 @@
#define IMA_FSNAME 0x0200
#define IMA_KEYRINGS 0x0400
#define IMA_LABEL 0x0800
+#define IMA_VALIDATE_ALGOS 0x1000
#define UNKNOWN 0
#define MEASURE 0x0001 /* same as IMA_MEASURE */
@@ -52,6 +53,8 @@ int ima_policy_flag;
static int temp_ima_appraise;
static int build_ima_appraise __ro_after_init;
+atomic_t ima_setxattr_allowed_hash_algorithms;
+
#define MAX_LSM_RULES 6
enum lsm_rule_types { LSM_OBJ_USER, LSM_OBJ_ROLE, LSM_OBJ_TYPE,
LSM_SUBJ_USER, LSM_SUBJ_ROLE, LSM_SUBJ_TYPE
@@ -79,6 +82,7 @@ struct ima_rule_entry {
bool (*uid_op)(kuid_t, kuid_t); /* Handlers for operators */
bool (*fowner_op)(kuid_t, kuid_t); /* uid_eq(), uid_gt(), uid_lt() */
int pcr;
+ unsigned int allowed_algos; /* bitfield of allowed hash algorithms */
struct {
void *rule; /* LSM file metadata specific */
char *args_p; /* audit value */
@@ -91,6 +95,14 @@ struct ima_rule_entry {
};
/*
+ * sanity check in case the kernels gains more hash algorithms that can
+ * fit in an unsigned int
+ */
+static_assert(
+ 8 * sizeof(unsigned int) >= HASH_ALGO__LAST,
+ "The bitfield allowed_algos in ima_rule_entry is too small to contain all the supported hash algorithms, consider using a bigger type");
+
+/*
* Without LSM specific knowledge, the default policy can only be
* written in terms of .action, .func, .mask, .fsmagic, .uid, and .fowner
*/
@@ -646,6 +658,7 @@ static int get_subaction(struct ima_rule_entry *rule, enum ima_hooks func)
* @pcr: set the pcr to extend
* @template_desc: the template that should be used for this rule
* @func_data: func specific data, may be NULL
+ * @allowed_algos: allowlist of hash algorithms for the IMA xattr
*
* Measure decision based on func/mask/fsmagic and LSM(subj/obj/type)
* conditions.
@@ -658,7 +671,7 @@ int ima_match_policy(struct user_namespace *mnt_userns, struct inode *inode,
const struct cred *cred, u32 secid, enum ima_hooks func,
int mask, int flags, int *pcr,
struct ima_template_desc **template_desc,
- const char *func_data)
+ const char *func_data, unsigned int *allowed_algos)
{
struct ima_rule_entry *entry;
int action = 0, actmask = flags | (flags << 1);
@@ -684,8 +697,11 @@ int ima_match_policy(struct user_namespace *mnt_userns, struct inode *inode,
action &= ~IMA_HASH;
if (ima_fail_unverifiable_sigs)
action |= IMA_FAIL_UNVERIFIABLE_SIGS;
- }
+ if (allowed_algos &&
+ entry->flags & IMA_VALIDATE_ALGOS)
+ *allowed_algos = entry->allowed_algos;
+ }
if (entry->action & IMA_DO_MASK)
actmask &= ~(entry->action | entry->action << 1);
@@ -706,24 +722,57 @@ int ima_match_policy(struct user_namespace *mnt_userns, struct inode *inode,
return action;
}
-/*
- * Initialize the ima_policy_flag variable based on the currently
- * loaded policy. Based on this flag, the decision to short circuit
- * out of a function or not call the function in the first place
- * can be made earlier.
+/**
+ * ima_update_policy_flags() - Update global IMA variables
+ *
+ * Update ima_policy_flag and ima_setxattr_allowed_hash_algorithms
+ * based on the currently loaded policy.
+ *
+ * With ima_policy_flag, the decision to short circuit out of a function
+ * or not call the function in the first place can be made earlier.
+ *
+ * With ima_setxattr_allowed_hash_algorithms, the policy can restrict the
+ * set of hash algorithms accepted when updating the security.ima xattr of
+ * a file.
+ *
+ * Context: called after a policy update and at system initialization.
*/
-void ima_update_policy_flag(void)
+void ima_update_policy_flags(void)
{
struct ima_rule_entry *entry;
+ int new_policy_flag = 0;
+ rcu_read_lock();
list_for_each_entry(entry, ima_rules, list) {
+ /*
+ * SETXATTR_CHECK rules do not implement a full policy check
+ * because rule checking would probably have an important
+ * performance impact on setxattr(). As a consequence, only one
+ * SETXATTR_CHECK can be active at a given time.
+ * Because we want to preserve that property, we set out to use
+ * atomic_cmpxchg. Either:
+ * - the atomic was non-zero: a setxattr hash policy is
+ * already enforced, we do nothing
+ * - the atomic was zero: no setxattr policy was set, enable
+ * the setxattr hash policy
+ */
+ if (entry->func == SETXATTR_CHECK) {
+ atomic_cmpxchg(&ima_setxattr_allowed_hash_algorithms,
+ 0, entry->allowed_algos);
+ /* SETXATTR_CHECK doesn't impact ima_policy_flag */
+ continue;
+ }
+
if (entry->action & IMA_DO_MASK)
- ima_policy_flag |= entry->action;
+ new_policy_flag |= entry->action;
}
+ rcu_read_unlock();
ima_appraise |= (build_ima_appraise | temp_ima_appraise);
if (!ima_appraise)
- ima_policy_flag &= ~IMA_APPRAISE;
+ new_policy_flag &= ~IMA_APPRAISE;
+
+ ima_policy_flag = new_policy_flag;
}
static int ima_appraise_flag(enum ima_hooks func)
@@ -889,7 +938,9 @@ void __init ima_init_policy(void)
ARRAY_SIZE(critical_data_rules),
IMA_DEFAULT_POLICY);
- ima_update_policy_flag();
+ atomic_set(&ima_setxattr_allowed_hash_algorithms, 0);
+
+ ima_update_policy_flags();
}
/* Make sure we have a valid policy, at least containing some rules. */
@@ -929,7 +980,7 @@ void ima_update_policy(void)
*/
kfree(arch_policy_entry);
}
- ima_update_policy_flag();
+ ima_update_policy_flags();
/* Custom IMA policy has been loaded */
ima_process_queued_keys();
@@ -946,7 +997,7 @@ enum {
Opt_fsuuid, Opt_uid_eq, Opt_euid_eq, Opt_fowner_eq,
Opt_uid_gt, Opt_euid_gt, Opt_fowner_gt,
Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt,
- Opt_appraise_type, Opt_appraise_flag,
+ Opt_appraise_type, Opt_appraise_flag, Opt_appraise_algos,
Opt_permit_directio, Opt_pcr, Opt_template, Opt_keyrings,
Opt_label, Opt_err
};
@@ -981,6 +1032,7 @@ static const match_table_t policy_tokens = {
{Opt_fowner_lt, "fowner<%s"},
{Opt_appraise_type, "appraise_type=%s"},
{Opt_appraise_flag, "appraise_flag=%s"},
+ {Opt_appraise_algos, "appraise_algos=%s"},
{Opt_permit_directio, "permit_directio"},
{Opt_pcr, "pcr=%s"},
{Opt_template, "template=%s"},
@@ -1081,7 +1133,8 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
return false;
if (entry->action != APPRAISE &&
- entry->flags & (IMA_DIGSIG_REQUIRED | IMA_MODSIG_ALLOWED | IMA_CHECK_BLACKLIST))
+ entry->flags & (IMA_DIGSIG_REQUIRED | IMA_MODSIG_ALLOWED |
+ IMA_CHECK_BLACKLIST | IMA_VALIDATE_ALGOS))
return false;
/*
@@ -1111,7 +1164,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
IMA_UID | IMA_FOWNER | IMA_FSUUID |
IMA_INMASK | IMA_EUID | IMA_PCR |
IMA_FSNAME | IMA_DIGSIG_REQUIRED |
- IMA_PERMIT_DIRECTIO))
+ IMA_PERMIT_DIRECTIO | IMA_VALIDATE_ALGOS))
return false;
break;
@@ -1123,7 +1176,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
IMA_INMASK | IMA_EUID | IMA_PCR |
IMA_FSNAME | IMA_DIGSIG_REQUIRED |
IMA_PERMIT_DIRECTIO | IMA_MODSIG_ALLOWED |
- IMA_CHECK_BLACKLIST))
+ IMA_CHECK_BLACKLIST | IMA_VALIDATE_ALGOS))
return false;
break;
@@ -1161,6 +1214,23 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
return false;
break;
+ case SETXATTR_CHECK:
+ /* any action other than APPRAISE is unsupported */
+ if (entry->action != APPRAISE)
+ return false;
+
+ /* SETXATTR_CHECK requires an appraise_algos parameter */
+ if (!(entry->flags & IMA_VALIDATE_ALGOS))
+ return false;
+
+ /*
+ * full policies are not supported, they would have too
+ * much of a performance impact
+ */
+ if (entry->flags & ~(IMA_FUNC | IMA_VALIDATE_ALGOS))
+ return false;
+
+ break;
default:
return false;
}
@@ -1173,6 +1243,34 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
return true;
}
+static unsigned int ima_parse_appraise_algos(char *arg)
+{
+ unsigned int res = 0;
+ int idx;
+ char *token;
+
+ while ((token = strsep(&arg, ",")) != NULL) {
+ idx = match_string(hash_algo_name, HASH_ALGO__LAST, token);
+
+ if (idx < 0) {
+ pr_err("unknown hash algorithm \"%s\"",
+ token);
+ return 0;
+ }
+
+ if (!crypto_has_alg(hash_algo_name[idx], 0, 0)) {
+ pr_err("unavailable hash algorithm \"%s\", check your kernel configuration",
+ token);
+ return 0;
+ }
+
+ /* Add the hash algorithm to the 'allowed' bitfield */
+ res |= (1U << idx);
+ }
+
+ return res;
+}
+
static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
{
struct audit_buffer *ab;
@@ -1294,6 +1392,8 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
entry->func = KEY_CHECK;
else if (strcmp(args[0].from, "CRITICAL_DATA") == 0)
entry->func = CRITICAL_DATA;
+ else if (strcmp(args[0].from, "SETXATTR_CHECK") == 0)
+ entry->func = SETXATTR_CHECK;
else
result = -EINVAL;
if (!result)
@@ -1508,6 +1608,25 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
else
result = -EINVAL;
break;
+ case Opt_appraise_algos:
+ ima_log_string(ab, "appraise_algos", args[0].from);
+
+ if (entry->allowed_algos) {
+ result = -EINVAL;
+ break;
+ }
+
+ entry->allowed_algos =
+ ima_parse_appraise_algos(args[0].from);
+ /* invalid or empty list of algorithms */
+ if (!entry->allowed_algos) {
+ result = -EINVAL;
+ break;
+ }
+
+ entry->flags |= IMA_VALIDATE_ALGOS;
+
+ break;
case Opt_permit_directio:
entry->flags |= IMA_PERMIT_DIRECTIO;
break;
@@ -1700,6 +1819,23 @@ static void ima_show_rule_opt_list(struct seq_file *m,
seq_printf(m, "%s%s", i ? "|" : "", opt_list->items[i]);
}
+static void ima_policy_show_appraise_algos(struct seq_file *m,
+ unsigned int allowed_hashes)
+{
+ int idx, list_size = 0;
+
+ for (idx = 0; idx < HASH_ALGO__LAST; idx++) {
+ if (!(allowed_hashes & (1U << idx)))
+ continue;
+
+ /* only add commas if the list contains multiple entries */
+ if (list_size++)
+ seq_puts(m, ",");
+
+ seq_puts(m, hash_algo_name[idx]);
+ }
+}
+
int ima_policy_show(struct seq_file *m, void *v)
{
struct ima_rule_entry *entry = v;
@@ -1811,6 +1947,12 @@ int ima_policy_show(struct seq_file *m, void *v)
seq_puts(m, " ");
}
+ if (entry->flags & IMA_VALIDATE_ALGOS) {
+ seq_puts(m, "appraise_algos=");
+ ima_policy_show_appraise_algos(m, entry->allowed_algos);
+ seq_puts(m, " ");
+ }
+
for (i = 0; i < MAX_LSM_RULES; i++) {
if (entry->lsm[i].rule) {
switch (i) {

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