[RFC,v1,1/1] audit: speed up syscall rule match while exiting syscall

[RFC,v1,1/1] audit: speed up syscall rule match while exiting syscall

[yang.yang29]

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From 82ebcf43481be21ee3e32ec1749b42f651737880 Mon Sep 17 00:00:00 2001
From: Yang Yang <yang.yang29@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@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

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Re: [RFC, v1, 1/1] audit: speed up syscall rule match while exiting syscall

[Paul Moore]

On Wed, Jan 13, 2021 at 7:39 AM <yang.yang29@zte.com.cn> wrote:
> From 82ebcf43481be21ee3e32ec1749b42f651737880 Mon Sep 17 00:00:00 2001
> From: Yang Yang <yang.yang29@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@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(-)

Before we go too far into a review of this patch, please provide some
performance measurements using a variety of rule counts, both common
and extreme, so that we can better judge the benefits of this patch.
The measurements should include both the rule add/delete time deltas
as well as the impact on the syscall invocations.  If non-obvious,
please also include how you performed the measurements and captured
the data.

These are good things to include in the commit description when
submitting patches focused on improving performance.

-- 
paul moore
www.paul-moore.com

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