Commit eb0782bb authored by liqiong's avatar liqiong Committed by Mimi Zohar
Browse files

ima: fix deadlock when traversing "ima_default_rules". 



The current IMA ruleset is identified by the variable "ima_rules"
that default to "&ima_default_rules". When loading a custom policy
for the first time, the variable is updated to "&ima_policy_rules"
instead. That update isn't RCU-safe, and deadlocks are possible.
Indeed, some functions like ima_match_policy() may loop indefinitely
when traversing "ima_default_rules" with list_for_each_entry_rcu().

When iterating over the default ruleset back to head, if the list
head is "ima_default_rules", and "ima_rules" have been updated to
"&ima_policy_rules", the loop condition (&entry->list != ima_rules)
stays always true, traversing won't terminate, causing a soft lockup
and RCU stalls.

Introduce a temporary value for "ima_rules" when iterating over
the ruleset to avoid the deadlocks.

Signed-off-by: default avatarliqiong <liqiong@nfschina.com>
Reviewed-by: default avatarTHOBY Simon <Simon.THOBY@viveris.fr>
Fixes: 38d859f9 ("IMA: policy can now be updated multiple times")
Reported-by: kernel test robot <lkp@intel.com> (Fix sparse: incompatible types in comparison expression.)
Signed-off-by: default avatarMimi Zohar <zohar@linux.ibm.com>
parent 6880fa6c

security/integrity/ima/ima_policy.c

+18 −9
Original line number Diff line number Diff line
@@ -228,7 +228,7 @@ static struct ima_rule_entry *arch_policy_entry __ro_after_init; 
static LIST_HEAD(ima_default_rules);

static LIST_HEAD(ima_policy_rules);

static LIST_HEAD(ima_temp_rules);

static struct list_head *ima_rules = &ima_default_rules;

static struct list_head __rcu *ima_rules = (struct list_head __rcu *)(&ima_default_rules);



static int ima_policy __initdata;
@@ -675,12 +675,14 @@ int ima_match_policy(struct user_namespace *mnt_userns, struct inode *inode, 
{

	struct ima_rule_entry *entry;

	int action = 0, actmask = flags | (flags << 1);

	struct list_head *ima_rules_tmp;



	if (template_desc && !*template_desc)

		*template_desc = ima_template_desc_current();



	rcu_read_lock();

	list_for_each_entry_rcu(entry, ima_rules, list) {

	ima_rules_tmp = rcu_dereference(ima_rules);

	list_for_each_entry_rcu(entry, ima_rules_tmp, list) {



		if (!(entry->action & actmask))

			continue;
@@ -741,9 +743,11 @@ void ima_update_policy_flags(void) 
{

	struct ima_rule_entry *entry;

	int new_policy_flag = 0;

	struct list_head *ima_rules_tmp;



	rcu_read_lock();

	list_for_each_entry(entry, ima_rules, list) {

	ima_rules_tmp = rcu_dereference(ima_rules);

	list_for_each_entry_rcu(entry, ima_rules_tmp, list) {

		/*

		 * SETXATTR_CHECK rules do not implement a full policy check

		 * because rule checking would probably have an important
@@ -968,10 +972,10 @@ void ima_update_policy(void) 


	list_splice_tail_init_rcu(&ima_temp_rules, policy, synchronize_rcu);



	if (ima_rules != policy) {

	if (ima_rules != (struct list_head __rcu *)policy) {

		ima_policy_flag = 0;

		ima_rules = policy;



		rcu_assign_pointer(ima_rules, policy);

		/*

		 * IMA architecture specific policy rules are specified

		 * as strings and converted to an array of ima_entry_rules
@@ -1061,7 +1065,7 @@ static int ima_lsm_rule_init(struct ima_rule_entry *entry, 
		pr_warn("rule for LSM \'%s\' is undefined\n",

			entry->lsm[lsm_rule].args_p);



		if (ima_rules == &ima_default_rules) {

		if (ima_rules == (struct list_head __rcu *)(&ima_default_rules)) {

			kfree(entry->lsm[lsm_rule].args_p);

			entry->lsm[lsm_rule].args_p = NULL;

			result = -EINVAL;
@@ -1768,9 +1772,11 @@ void *ima_policy_start(struct seq_file *m, loff_t *pos) 
{

	loff_t l = *pos;

	struct ima_rule_entry *entry;

	struct list_head *ima_rules_tmp;



	rcu_read_lock();

	list_for_each_entry_rcu(entry, ima_rules, list) {

	ima_rules_tmp = rcu_dereference(ima_rules);

	list_for_each_entry_rcu(entry, ima_rules_tmp, list) {

		if (!l--) {

			rcu_read_unlock();

			return entry;
@@ -1789,7 +1795,8 @@ void *ima_policy_next(struct seq_file *m, void *v, loff_t *pos) 
	rcu_read_unlock();

	(*pos)++;



	return (&entry->list == ima_rules) ? NULL : entry;

	return (&entry->list == &ima_default_rules ||

		&entry->list == &ima_policy_rules) ? NULL : entry;

}



void ima_policy_stop(struct seq_file *m, void *v)
@@ -2014,6 +2021,7 @@ bool ima_appraise_signature(enum kernel_read_file_id id) 
	struct ima_rule_entry *entry;

	bool found = false;

	enum ima_hooks func;

	struct list_head *ima_rules_tmp;



	if (id >= READING_MAX_ID)

		return false;
@@ -2021,7 +2029,8 @@ bool ima_appraise_signature(enum kernel_read_file_id id) 
	func = read_idmap[id] ?: FILE_CHECK;



	rcu_read_lock();

	list_for_each_entry_rcu(entry, ima_rules, list) {

	ima_rules_tmp = rcu_dereference(ima_rules);

	list_for_each_entry_rcu(entry, ima_rules_tmp, list) {

		if (entry->action != APPRAISE)

			continue;