From: liqiong liqiong@nfschina.com

mainline inclusion from mainline-v5.16-rc1 commit eb0782bbdfd0d7c4786216659277c3fd585afc0e category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I9AAM6 CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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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: 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 Conflicts: security/integrity/ima/ima_policy.c [Context conflicts. Besides an additional pair of rcu_read_lock and unlock has been added to ima_update_policy_flag to mitigate a 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: GUO Zihua guozihua@huawei.com --- security/integrity/ima/ima_policy.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c index 08eae4df759e..3098894ea026 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -196,7 +196,7 @@ static struct ima_rule_entry secure_boot_rules[] __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;

@@ -515,9 +515,11 @@ 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;

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; @@ -560,11 +562,15 @@ 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) @@ -683,9 +689,9 @@ 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_update_policy_flag(); } @@ -760,7 +766,7 @@ static int ima_lsm_rule_init(struct ima_rule_entry *entry, pr_warn("rule for LSM '%s' is undefined\n", (char *)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; @@ -1188,9 +1194,11 @@ 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; @@ -1209,7 +1217,8 @@ 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)