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Message-Id: <a8356e46aed7213128e84a888170391adb6afe30.1391449825.git.luto@amacapital.net>
Date: Mon, 3 Feb 2014 09:53:23 -0800
From: Andy Lutomirski <luto@...capital.net>
To: linux-audit@...hat.com, linux-kernel@...r.kernel.org
Cc: Andy Lutomirski <luto@...capital.net>,
Andi Kleen <andi@...stfloor.org>,
Oleg Nesterov <oleg@...hat.com>,
Steve Grubb <sgrubb@...hat.com>, Eric Paris <eparis@...hat.com>
Subject: [PATCH] audit: Only use the syscall slowpath when syscall audit rules exist
This toggles TIF_SYSCALL_AUDIT as needed when rules change instead of
leaving it set whenever rules might be set in the future. This reduces
syscall latency from >60ns to closer to 40ns on my laptop.
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Steve Grubb <sgrubb@...hat.com>
Cc: Eric Paris <eparis@...hat.com>
Signed-off-by: Andy Lutomirski <luto@...capital.net>
---
This is not the best-tested patch in the world. Someone who actually
knows how to use syscall auditing should probably give it a spin. It
fixes an IMO huge performance issue, though.
include/linux/audit.h | 9 +++++--
kernel/auditfilter.c | 4 ++--
kernel/auditsc.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++---
3 files changed, 71 insertions(+), 7 deletions(-)
diff --git a/include/linux/audit.h b/include/linux/audit.h
index a406419..534ba85 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -298,7 +298,9 @@ static inline void audit_mmap_fd(int fd, int flags)
__audit_mmap_fd(fd, flags);
}
-extern int audit_n_rules;
+extern void audit_inc_n_rules(void);
+extern void audit_dec_n_rules(void);
+
extern int audit_signals;
#else /* CONFIG_AUDITSYSCALL */
static inline int audit_alloc(struct task_struct *task)
@@ -404,7 +406,10 @@ static inline void audit_mmap_fd(int fd, int flags)
{ }
static inline void audit_ptrace(struct task_struct *t)
{ }
-#define audit_n_rules 0
+static inline void audit_inc_n_rules(void)
+{ }
+static inline void audit_dec_n_rules(void)
+{ }
#define audit_signals 0
#endif /* CONFIG_AUDITSYSCALL */
diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
index 51f3fd4..0ce531d 100644
--- a/kernel/auditfilter.c
+++ b/kernel/auditfilter.c
@@ -903,7 +903,7 @@ static inline int audit_add_rule(struct audit_entry *entry)
}
#ifdef CONFIG_AUDITSYSCALL
if (!dont_count)
- audit_n_rules++;
+ audit_inc_n_rules();
if (!audit_match_signal(entry))
audit_signals++;
@@ -955,7 +955,7 @@ static inline int audit_del_rule(struct audit_entry *entry)
#ifdef CONFIG_AUDITSYSCALL
if (!dont_count)
- audit_n_rules--;
+ audit_dec_n_rules();
if (!audit_match_signal(entry))
audit_signals--;
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 90594c9..363d0bb 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -79,8 +79,15 @@
/* no execve audit message should be longer than this (userspace limits) */
#define MAX_EXECVE_AUDIT_LEN 7500
-/* number of audit rules */
-int audit_n_rules;
+/*
+ * number of audit rules
+ *
+ * n_rules_lock protects audit_n_rules. It also prevents audit_alloc from
+ * racing against changes to audit_n_rules: to change someone else's
+ * audit_context or TIF_SYSCALL_AUDIT, you need write_lock(&n_rules_lock).
+ */
+static DEFINE_RWLOCK(n_rules_lock);
+static int audit_n_rules;
/* determines whether we collect data for signals sent */
int audit_signals;
@@ -911,6 +918,47 @@ static inline struct audit_context *audit_alloc_context(enum audit_state state)
return context;
}
+void audit_inc_n_rules()
+{
+ struct task_struct *p, *g;
+
+ write_lock(&n_rules_lock);
+
+ if (audit_n_rules++ != 0)
+ goto out; /* The overall state isn't changing. */
+
+ read_lock(&tasklist_lock);
+ do_each_thread(g, p) {
+ if (p->audit_context)
+ set_tsk_thread_flag(p, TIF_SYSCALL_AUDIT);
+ } while_each_thread(g, p);
+ read_unlock(&tasklist_lock);
+
+out:
+ write_unlock(&n_rules_lock);
+}
+
+void audit_dec_n_rules()
+{
+ struct task_struct *p, *g;
+
+ write_lock(&n_rules_lock);
+ --audit_n_rules;
+ BUG_ON(audit_n_rules < 0);
+
+ if (audit_n_rules != 0)
+ goto out; /* The overall state isn't changing. */
+
+ read_lock(&tasklist_lock);
+ do_each_thread(g, p) {
+ clear_tsk_thread_flag(p, TIF_SYSCALL_AUDIT);
+ } while_each_thread(g, p);
+ read_unlock(&tasklist_lock);
+
+out:
+ write_unlock(&n_rules_lock);
+}
+
/**
* audit_alloc - allocate an audit context block for a task
* @tsk: task
@@ -931,6 +979,11 @@ int audit_alloc(struct task_struct *tsk)
state = audit_filter_task(tsk, &key);
if (state == AUDIT_DISABLED) {
+ /*
+ * There is no relevant race against inc/dec_n_rules
+ * here -- inc won't set TIF_SYSCALL_AUDIT, and, if dec
+ * clears it redundantly, there's no harm done.
+ */
clear_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT);
return 0;
}
@@ -942,8 +995,14 @@ int audit_alloc(struct task_struct *tsk)
}
context->filterkey = key;
+ read_lock(&n_rules_lock);
tsk->audit_context = context;
- set_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT);
+ if (audit_n_rules)
+ set_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT);
+ else
+ clear_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT);
+ read_unlock(&n_rules_lock);
+
return 0;
}
--
1.8.5.3
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