timerfd: Only check CAP_WAKE_ALARM when it is needed

stephensmalley · KAGA-KOKO · commit 25b68a8f0ab1 · 2017-03-01T12:53:44.000+01:00
timerfd_create() and do_timerfd_settime() evaluate capable(CAP_WAKE_ALARM) unconditionally although CAP_WAKE_ALARM is only required for CLOCK_REALTIME_ALARM and CLOCK_BOOTTIME_ALARM. This can cause extraneous audit messages when using a LSM such as SELinux, incorrectly causes PF_SUPERPRIV to be set even when no privilege was exercised, and is inefficient. Flip the order of the tests in both functions so that we only call capable() if the capability is truly required for the operation. Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov> Cc: linux-security-module@vger.kernel.org Cc: selinux@tycho.nsa.gov Link: http://lkml.kernel.org/r/1487344439-22293-1-git-send-email-sds@tycho.nsa.gov Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/fs/timerfd.c b/fs/timerfd.c
@@ -400,9 +400,9 @@ SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 	     clockid != CLOCK_BOOTTIME_ALARM))
 		return -EINVAL;
 
-	if (!capable(CAP_WAKE_ALARM) &&
-	    (clockid == CLOCK_REALTIME_ALARM ||
-	     clockid == CLOCK_BOOTTIME_ALARM))
+	if ((clockid == CLOCK_REALTIME_ALARM ||
+	     clockid == CLOCK_BOOTTIME_ALARM) &&
+	    !capable(CAP_WAKE_ALARM))
 		return -EPERM;
 
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
@@ -449,7 +449,7 @@ static int do_timerfd_settime(int ufd, int flags,
 		return ret;
 	ctx = f.file->private_data;
 
-	if (!capable(CAP_WAKE_ALARM) && isalarm(ctx)) {
+	if (isalarm(ctx) && !capable(CAP_WAKE_ALARM)) {
 		fdput(f);
 		return -EPERM;
 	}
