AUDIT: Fix livelock in audit_serial().

The tricks with atomic_t were bizarre. Just do it sensibly instead. Signed-off-by: David Woodhouse <dwmw2@infradead.org>

AUDIT: Fix livelock in audit_serial().
The tricks with atomic_t were bizarre. Just do it sensibly instead. Signed-off-by: David Woodhouse <dwmw2@infradead.org>
David Woodhouse
1 parent 351bb72259
Showing 1 changed file with 10 additions and 11 deletions Side-by-side Diff
kernel/audit.c
@@ -610,26 +610,25 @@
  * (timestamp,serial) tuple is unique for each syscall and is live from
  * syscall entry to syscall exit.
  *
- * Atomic values are only guaranteed to be 24-bit, so we count down.
- *
  * NOTE: Another possibility is to store the formatted records off the
  * audit context (for those records that have a context), and emit them
  * all at syscall exit.  However, this could delay the reporting of
  * significant errors until syscall exit (or never, if the system
  * halts). */
+
 unsigned int audit_serial(void)
 {
-	static atomic_t serial = ATOMIC_INIT(0xffffff);
-	unsigned int a, b;
+	static spinlock_t serial_lock = SPIN_LOCK_UNLOCKED;
+	static unsigned int serial = 0;
  
-	do {
-		a = atomic_read(&serial);
-		if (atomic_dec_and_test(&serial))
-			atomic_set(&serial, 0xffffff);
-		b = atomic_read(&serial);
-	} while (b != a - 1);
+	unsigned long flags;
+	unsigned int ret;
  
-	return 0xffffff - b;
+	spin_lock_irqsave(&serial_lock, flags);
+	ret = serial++;
+	spin_unlock_irqrestore(&serial_lock, flags);
+
+	return ret;
 }
  
 static inline void audit_get_stamp(struct audit_context *ctx,
...	...	@@ -610,26 +610,25 @@
610	610	* (timestamp,serial) tuple is unique for each syscall and is live from
611	611	* syscall entry to syscall exit.
612	612	*
613		- * Atomic values are only guaranteed to be 24-bit, so we count down.
614		- *
615	613	* NOTE: Another possibility is to store the formatted records off the
616	614	* audit context (for those records that have a context), and emit them
617	615	* all at syscall exit. However, this could delay the reporting of
618	616	* significant errors until syscall exit (or never, if the system
619	617	* halts). */
	618	+
620	619	unsigned int audit_serial(void)
621	620	{
622		- static atomic_t serial = ATOMIC_INIT(0xffffff);
623		- unsigned int a, b;
	621	+ static spinlock_t serial_lock = SPIN_LOCK_UNLOCKED;
	622	+ static unsigned int serial = 0;
624	623
625		- do {
626		- a = atomic_read(&serial);
627		- if (atomic_dec_and_test(&serial))
628		- atomic_set(&serial, 0xffffff);
629		- b = atomic_read(&serial);
630		- } while (b != a - 1);
	624	+ unsigned long flags;
	625	+ unsigned int ret;
631	626
632		- return 0xffffff - b;
	627	+ spin_lock_irqsave(&serial_lock, flags);
	628	+ ret = serial++;
	629	+ spin_unlock_irqrestore(&serial_lock, flags);
	630	+
	631	+ return ret;
633	632	}
634	633
635	634	static inline void audit_get_stamp(struct audit_context *ctx,