From 4bef6e617dbc92c665ccbaf7a6ad3f504def3253 Mon Sep 17 00:00:00 2001 From: liqiong Date: Sat, 9 Oct 2021 18:38:21 +0800 Subject: [PATCH] ima: fix deadlock when traversing "ima_default_rules". [ 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. Signed-off-by: liqiong Reviewed-by: THOBY Simon Fixes: 38d859f991f3 ("IMA: policy can now be updated multiple times") Reported-by: kernel test robot (Fix sparse: incompatible types in comparison expression.) Signed-off-by: Mimi Zohar Signed-off-by: Sasha Levin --- security/integrity/ima/ima_policy.c | 27 ++++++++++++++++++--------- 1 file changed, 18 insertions(+), 9 deletions(-) diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c index 87b9b71..12e8adc 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -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; -- 2.7.4