[RFC,v2,1/1] audit: speed up syscall rule match while exiting syscall

[RFC,v2,1/1] audit: speed up syscall rule match while exiting syscall

[yang.yang29]

[-- Attachment #1.1: Type: text/plain, Size: 4407 bytes --]

From 72f3ecde58edb03d76cb359607fef98c1663d481 Mon Sep 17 00:00:00 2001
From: Yang Yang <yang.yang29@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@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

[-- Attachment #2: Type: text/plain, Size: 102 bytes --]

--
Linux-audit mailing list
Linux-audit@redhat.com
https://www.redhat.com/mailman/listinfo/linux-audit

Re: [RFC,v2,1/1] audit: speed up syscall rule match while exiting syscall

[Paul Moore]

On Thu, Jan 21, 2021 at 8:54 AM <yang.yang29@zte.com.cn> wrote:
>
> From 72f3ecde58edb03d76cb359607fef98c1663d481 Mon Sep 17 00:00:00 2001
> From: Yang Yang <yang.yang29@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@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/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

I'm going to reply to your other email where we are discussing the
performance of this patch, but I wanted to make one comment about the
approach you've taken with the update_auditing_syscall() here.

First, naming things is hard, but the chosen name is not a good one in
my opinion.  Something like audit_rule_syscall_mask_update() would
probably be a better fit.

Second, in order to minimize preprocessor clutter, it is better to use
the following pattern:

  #ifdef CONFIG_FOO
  int func(int arg)
  {
    /* important stuff */
  }
  #else
  int func(int arg)
  {
    return 0; /* appropriate return value */
  }
  #endif

There are probably a few other comments on this patch, but I want us
to discuss the performance impacts of this first as I'm not convinced
this is a solution we want upstream.

-- 
paul moore
www.paul-moore.com

Re: [RFC, v2, 1/1] audit: speed up syscall rule match while exiting syscall

[Paul Moore]

On Thu, Jan 21, 2021 at 8:54 AM <yang.yang29@zte.com.cn> wrote:
>
> From 72f3ecde58edb03d76cb359607fef98c1663d481 Mon Sep 17 00:00:00 2001
> From: Yang Yang <yang.yang29@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@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/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

I'm going to reply to your other email where we are discussing the
performance of this patch, but I wanted to make one comment about the
approach you've taken with the update_auditing_syscall() here.

First, naming things is hard, but the chosen name is not a good one in
my opinion.  Something like audit_rule_syscall_mask_update() would
probably be a better fit.

Second, in order to minimize preprocessor clutter, it is better to use
the following pattern:

  #ifdef CONFIG_FOO
  int func(int arg)
  {
    /* important stuff */
  }
  #else
  int func(int arg)
  {
    return 0; /* appropriate return value */
  }
  #endif

There are probably a few other comments on this patch, but I want us
to discuss the performance impacts of this first as I'm not convinced
this is a solution we want upstream.

-- 
paul moore
www.paul-moore.com

--
Linux-audit mailing list
Linux-audit@redhat.com
https://www.redhat.com/mailman/listinfo/linux-audit