[RFC,v2,1/1] audit: speed up syscall rule match while exiting syscall
From 72f3ecde58edb03d76cb359607fef98c1663d481 Mon Sep 17 00:00:00 2001
From: Yang Yang <yang.yang29(a)zte.com.cn>
Date: Thu, 21 Jan 2021 21:05:04 +0800
Subject: [PATCH] [RFC,v2,1/1] speed up syscall rule match while exiting syscall
audit_filter_syscall() traverses struct list_head audit_filter_list to find
out whether current syscall match one rule. This takes o(n), which is not
necessary, specially for user who add a very few syscall rules. On the other
hand, user may not much care about rule add/delete speed. So do o(n)
calculate at rule changing, and ease the burden of audit_filter_syscall().
Define audit_syscall[NR_syscalls], every element stands for one syscall.
audit_filter_syscall() checks audit_syscall[NR_syscalls].
audit_syscall[n] == 0 indicates no rule audit syscall n, do a quick exit.
audit_syscall[n] > 0 indicates at least one rule audit syscall n.
audit_syscall[n] update when syscall rule changes.
Signed-off-by: Yang Yang <yang.yang29(a)zte.com.cn>
---
include/linux/audit.h | 2 ++
kernel/audit.c | 4 ++++
kernel/auditfilter.c | 30 ++++++++++++++++++++++++++++++
kernel/auditsc.c | 5 ++++-
4 files changed, 40 insertions(+), 1 deletion(-)
diff --git a/include/linux/audit.h b/include/linux/audit.h
index 82b7c11..7885531 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -549,6 +549,8 @@ static inline void audit_log_nfcfg(const char *name, u8 af,
extern int audit_n_rules;
extern int audit_signals;
+extern u32 auditing_syscall[NR_syscalls];
+extern int audit_in_mask(const struct audit_krule *rule, unsigned long val);
#else /* CONFIG_AUDITSYSCALL */
static inline int audit_alloc(struct task_struct *task)
{
diff --git a/kernel/audit.c b/kernel/audit.c
index 1ffc2e0..07f4590 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -208,6 +208,10 @@ struct audit_reply {
struct sk_buff *skb;
};
+#ifdef CONFIG_AUDITSYSCALL
+u32 auditing_syscall[NR_syscalls] = {0};
+#endif
+
/**
* auditd_test_task - Check to see if a given task is an audit daemon
* @task: the task to check
diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
index 333b3bc..9d3e703 100644
--- a/kernel/auditfilter.c
+++ b/kernel/auditfilter.c
@@ -926,6 +926,28 @@ static struct audit_entry *audit_find_rule(struct audit_entry
*entry,
static u64 prio_low = ~0ULL/2;
static u64 prio_high = ~0ULL/2 - 1;
+#ifdef CONFIG_AUDITSYSCALL
+static inline void update_auditing_syscall(struct audit_krule rule, bool add)
+{
+ int i;
+
+ /* syscall rule with type AUDIT_FILTER_EXIT */
+ if (rule.listnr == AUDIT_FILTER_EXIT && !rule.watch && !rule.tree) {
+ for (i = 0; i < NR_syscalls; i++) {
+ /* whether this rule include one syscall */
+ if (unlikely(audit_in_mask(&rule, i))) {
+ if (add == true)
+ auditing_syscall[i]++;
+ else
+ auditing_syscall[i]--;
+ }
+ }
+ }
+
+ return;
+}
+#endif
+
/* Add rule to given filterlist if not a duplicate. */
static inline int audit_add_rule(struct audit_entry *entry)
{
@@ -957,6 +979,10 @@ static inline int audit_add_rule(struct audit_entry *entry)
return err;
}
+#ifdef CONFIG_AUDITSYSCALL
+ update_auditing_syscall(entry->rule, true);
+#endif
+
if (watch) {
/* audit_filter_mutex is dropped and re-taken during this call */
err = audit_add_watch(&entry->rule, &list);
@@ -1035,6 +1061,10 @@ int audit_del_rule(struct audit_entry *entry)
goto out;
}
+#ifdef CONFIG_AUDITSYSCALL
+ update_auditing_syscall(e->rule, false);
+#endif
+
if (e->rule.watch)
audit_remove_watch_rule(&e->rule);
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index ce8c9e2..90490aa 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -783,7 +783,7 @@ static enum audit_state audit_filter_task(struct task_struct *tsk,
char **key)
return AUDIT_BUILD_CONTEXT;
}
-static int audit_in_mask(const struct audit_krule *rule, unsigned long val)
+int audit_in_mask(const struct audit_krule *rule, unsigned long val)
{
int word, bit;
@@ -814,6 +814,9 @@ static enum audit_state audit_filter_syscall(struct task_struct *tsk,
if (auditd_test_task(tsk))
return AUDIT_DISABLED;
+ if (!auditing_syscall[ctx->major])
+ return AUDIT_BUILD_CONTEXT;
+
rcu_read_lock();
list_for_each_entry_rcu(e, list, list) {
if (audit_in_mask(&e->rule, ctx->major) &&
--
2.15.2