On 8/27/21 11:10 AM, liqiong wrote: > Hi Simon, > > Thanks for your patient, i learn a lot. If the commit message > does work, i would resubmit the patch. Here is the whole patch: > > > 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@xxxxxxxxxxxx> > --- > security/integrity/ima/ima_policy.c | 17 ++++++++++++----- > 1 file changed, 12 insertions(+), 5 deletions(-) > > diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c > index fd5d46e511f1..e92b197bfd3c 100644 > --- a/security/integrity/ima/ima_policy.c > +++ b/security/integrity/ima/ima_policy.c > @@ -662,12 +662,14 @@ 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; > @@ -919,8 +921,8 @@ void ima_update_policy(void) > > if (ima_rules != 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 > @@ -1649,9 +1651,11 @@ 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; > @@ -1670,7 +1674,8 @@ 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) > @@ -1872,6 +1877,7 @@ 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; > @@ -1879,7 +1885,8 @@ 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; > > Reviewed-By: THOBY Simon <Simon.THOBY@xxxxxxxxxx>