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ima: fix deadlock when traversing "ima_default_rules".

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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: liqiong <liqiong@nfschina.com>
Reviewed-by: THOBY Simon <Simon.THOBY@viveris.fr>
Fixes: 38d859f991 ("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: Mimi Zohar <zohar@linux.ibm.com>
This commit is contained in:
liqiong 2021-10-09 18:38:21 +08:00 committed by Mimi Zohar
parent 6880fa6c56
commit eb0782bbdf
1 changed files with 18 additions and 9 deletions
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27
security/integrity/ima/ima_policy.c
View file

@ -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;