From: liqiong liqiong@nfschina.com

[ Upstream commit eb0782bbdfd0d7c4786216659277c3fd585afc0e ]

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.

Addition:

A rcu_read_lock pair is added within ima_update_policy_flag to avoid suspicious RCU usage warning. This pair of RCU lock was added with commit 4f2946aa0c45 ("IMA: introduce a new policy option func=SETXATTR_CHECK") on mainstream.

Signed-off-by: liqiong liqiong@nfschina.com Reviewed-by: THOBY Simon Simon.THOBY@viveris.fr Fixes: 38d859f991f3 ("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 Signed-off-by: GUO Zihua guozihua@huawei.com --- security/integrity/ima/ima_policy.c | 29 ++++++++++++++++++++--------- 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c index 1c403e8a8044..4f5d44037081 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -210,7 +210,7 @@ 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;

@@ -648,12 +648,14 @@ int ima_match_policy(struct inode *inode, const struct cred *cred, u32 secid, { struct ima_rule_entry *entry; int action = 0, actmask = flags | (flags << 1); + struct list_head *ima_rules_tmp;

if (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; @@ -701,11 +703,15 @@ int ima_match_policy(struct inode *inode, const struct cred *cred, u32 secid, void ima_update_policy_flag(void) { struct ima_rule_entry *entry; + struct list_head *ima_rules_tmp;

- list_for_each_entry(entry, ima_rules, list) { + rcu_read_lock(); + ima_rules_tmp = rcu_dereference(ima_rules); + list_for_each_entry_rcu(entry, ima_rules_tmp, list) { if (entry->action & IMA_DO_MASK) ima_policy_flag |= entry->action; } + rcu_read_unlock();

ima_appraise |= (build_ima_appraise | temp_ima_appraise); if (!ima_appraise) @@ -898,10 +904,10 @@ 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 @@ -989,7 +995,7 @@ 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; @@ -1598,9 +1604,11 @@ 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; @@ -1619,7 +1627,8 @@ 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) @@ -1823,6 +1832,7 @@ 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; @@ -1834,7 +1844,8 @@ 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;