posix-timers: Take compat timer_gettime(2) to native one

... and get rid of set_fs() in there
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20170607084241.28657-11-viro@ZenIV.linux.org.uk

kernel/compat.c

@@ -635,23 +635,6 @@ COMPAT_SYSCALL_DEFINE3(timer_create, clockid_t, which_clock,
 	return sys_timer_create(which_clock, event, created_timer_id);
 }
 
-COMPAT_SYSCALL_DEFINE2(timer_gettime, timer_t, timer_id,
-		       struct compat_itimerspec __user *, setting)
-{
-	long err;
-	mm_segment_t oldfs;
-	struct itimerspec ts;
-
-	oldfs = get_fs();
-	set_fs(KERNEL_DS);
-	err = sys_timer_gettime(timer_id,
-				(struct itimerspec __user *) &ts);
-	set_fs(oldfs);
-	if (!err && put_compat_itimerspec(setting, &ts))
-		return -EFAULT;
-	return err;
-}
-
 COMPAT_SYSCALL_DEFINE2(clock_settime, clockid_t, which_clock,
 		       struct compat_timespec __user *, tp)
 {

kernel/time/posix-stubs.c

@@ -43,6 +43,7 @@ SYS_NI(alarm);
 #endif
 COMPAT_SYS_NI(clock_adjtime);
 COMPAT_SYS_NI(timer_settime);
+COMPAT_SYS_NI(timer_gettime);
 
 /*
  * We preserve minimal support for CLOCK_REALTIME and CLOCK_MONOTONIC

kernel/time/posix-timers.c

@@ -690,11 +690,8 @@ void common_timer_get(struct k_itimer *timr, struct itimerspec64 *cur_setting)
 }
 
 /* Get the time remaining on a POSIX.1b interval timer. */
-SYSCALL_DEFINE2(timer_gettime, timer_t, timer_id,
-		struct itimerspec __user *, setting)
+static int do_timer_gettime(timer_t timer_id,  struct itimerspec64 *setting)
 {
-	struct itimerspec64 cur_setting64;
-	struct itimerspec cur_setting;
 	struct k_itimer *timr;
 	const struct k_clock *kc;
 	unsigned long flags;
@@ -704,21 +701,49 @@ SYSCALL_DEFINE2(timer_gettime, timer_t, timer_id,
 	if (!timr)
 		return -EINVAL;
 
-	memset(&cur_setting64, 0, sizeof(cur_setting64));
+	memset(setting, 0, sizeof(*setting));
 	kc = timr->kclock;
 	if (WARN_ON_ONCE(!kc || !kc->timer_get))
 		ret = -EINVAL;
 	else
-		kc->timer_get(timr, &cur_setting64);
+		kc->timer_get(timr, setting);
 
 	unlock_timer(timr, flags);
+	return ret;
+}
 
+/* Get the time remaining on a POSIX.1b interval timer. */
+SYSCALL_DEFINE2(timer_gettime, timer_t, timer_id,
+		struct itimerspec __user *, setting)
+{
+	struct itimerspec64 cur_setting64;
+
+	int ret = do_timer_gettime(timer_id, &cur_setting64);
+	if (!ret) {
+		struct itimerspec cur_setting;
 		cur_setting = itimerspec64_to_itimerspec(&cur_setting64);
-	if (!ret && copy_to_user(setting, &cur_setting, sizeof (cur_setting)))
-		return -EFAULT;
+		if (copy_to_user(setting, &cur_setting, sizeof (cur_setting)))
+			ret = -EFAULT;
+	}
+	return ret;
+}
+
+#ifdef CONFIG_COMPAT
+COMPAT_SYSCALL_DEFINE2(timer_gettime, timer_t, timer_id,
+		       struct compat_itimerspec __user *, setting)
+{
+	struct itimerspec64 cur_setting64;
 
+	int ret = do_timer_gettime(timer_id, &cur_setting64);
+	if (!ret) {
+		struct itimerspec cur_setting;
+		cur_setting = itimerspec64_to_itimerspec(&cur_setting64);
+		if (put_compat_itimerspec(setting, &cur_setting))
+			ret = -EFAULT;
+	}
 	return ret;
 }
+#endif
 
 /*
  * Get the number of overruns of a POSIX.1b interval timer.  This is to