[RFC,v1,1/1] audit: speed up syscall rule match while exiting syscall
From 82ebcf43481be21ee3e32ec1749b42f651737880 Mon Sep 17 00:00:00 2001
From: Yang Yang <yang.yang29(a)zte.com.cn>
Date: Wed, 13 Jan 2021 20:18:04 +0800
Subject: [PATCH] [RFC,v1,1/1] speed up syscall rule match while exiting syscall
If user add any syscall rule, in all syscalls, 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 | 2 ++
kernel/auditfilter.c | 16 ++++++++++++++++
kernel/auditsc.c | 9 ++++++++-
4 files changed, 28 insertions(+), 1 deletion(-)
diff --git a/include/linux/audit.h b/include/linux/audit.h
index 82b7c11..56a8c61 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 audit_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..d233a95 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -208,6 +208,8 @@ struct audit_reply {
struct sk_buff *skb;
};
+u32 audit_syscall[NR_syscalls] = {0};
+
/**
* 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..c7e60cd 100644
--- a/kernel/auditfilter.c
+++ b/kernel/auditfilter.c
@@ -936,6 +936,7 @@ static inline int audit_add_rule(struct audit_entry *entry)
int err = 0;
#ifdef CONFIG_AUDITSYSCALL
int dont_count = 0;
+ int i = 0;
/* If any of these, don't count towards total */
switch(entry->rule.listnr) {
@@ -957,6 +958,13 @@ static inline int audit_add_rule(struct audit_entry *entry)
return err;
}
+#ifdef CONFIG_AUDITSYSCALL
+ if (entry->rule.listnr == AUDIT_FILTER_EXIT && !watch && !tree)
{
+ for (i = 0; i < NR_syscalls; i++)
+ audit_syscall[i] += !(!audit_in_mask(&entry->rule, i));
+ }
+#endif
+
if (watch) {
/* audit_filter_mutex is dropped and re-taken during this call */
err = audit_add_watch(&entry->rule, &list);
@@ -1018,6 +1026,7 @@ int audit_del_rule(struct audit_entry *entry)
int ret = 0;
#ifdef CONFIG_AUDITSYSCALL
int dont_count = 0;
+ int i = 0;
/* If any of these, don't count towards total */
switch(entry->rule.listnr) {
@@ -1035,6 +1044,13 @@ int audit_del_rule(struct audit_entry *entry)
goto out;
}
+#ifdef CONFIG_AUDITSYSCALL
+ if (entry->rule.listnr == AUDIT_FILTER_EXIT && !e->rule.watch
&& !e->rule.tree) {
+ for (i = 0; i < NR_syscalls; i++)
+ audit_syscall[i] -= !(!audit_in_mask(&entry->rule, i));
+ }
+#endif
+
if (e->rule.watch)
audit_remove_watch_rule(&e->rule);
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index ce8c9e2..2a74436 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 +814,13 @@ static enum audit_state audit_filter_syscall(struct task_struct
*tsk,
if (auditd_test_task(tsk))
return AUDIT_DISABLED;
+ mutex_lock(&audit_filter_mutex);
+ if (!audit_syscall[ctx->major]) {
+ mutex_unlock(&audit_filter_mutex);
+ return AUDIT_BUILD_CONTEXT;
+ }
+ mutex_unlock(&audit_filter_mutex);
+
rcu_read_lock();
list_for_each_entry_rcu(e, list, list) {
if (audit_in_mask(&e->rule, ctx->major) &&
--
2.15.2