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Commit 849151dd authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

compat: nanosleep: Clarify error handling 



The error handling in compat_sys_nanosleep() is correct, but
completely non obvious. Document it and restrict it to the
-ERESTART_RESTARTBLOCK return value for clarity.

Reported-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 40bea039

kernel/compat.c

+21 −3
Original line number Diff line number Diff line
@@ -226,7 +226,7 @@ static long compat_nanosleep_restart(struct restart_block *restart) 
	ret = hrtimer_nanosleep_restart(restart);

	set_fs(oldfs);



	if (ret) {

	if (ret == -ERESTART_RESTARTBLOCK) {

		rmtp = restart->nanosleep.compat_rmtp;



		if (rmtp && compat_put_timespec(&rmt, rmtp))
@@ -256,7 +256,26 @@ COMPAT_SYSCALL_DEFINE2(nanosleep, struct compat_timespec __user *, rqtp, 
				HRTIMER_MODE_REL, CLOCK_MONOTONIC);

	set_fs(oldfs);



	if (ret) {

	/*

	 * hrtimer_nanosleep() can only return 0 or

	 * -ERESTART_RESTARTBLOCK here because:

	 *

	 * - we call it with HRTIMER_MODE_REL and therefor exclude the

	 *   -ERESTARTNOHAND return path.

	 *

	 * - we supply the rmtp argument from the task stack (due to

	 *   the necessary compat conversion. So the update cannot

	 *   fail, which excludes the -EFAULT return path as well. If

	 *   it fails nevertheless we have a bigger problem and wont

	 *   reach this place anymore.

	 *

	 * - if the return value is 0, we do not have to update rmtp

	 *    because there is no remaining time.

	 *

	 * We check for -ERESTART_RESTARTBLOCK nevertheless if the

	 * core implementation decides to return random nonsense.

	 */

	if (ret == -ERESTART_RESTARTBLOCK) {

		struct restart_block *restart

			= &current_thread_info()->restart_block;
@@ -266,7 +285,6 @@ COMPAT_SYSCALL_DEFINE2(nanosleep, struct compat_timespec __user *, rqtp, 
		if (rmtp && compat_put_timespec(&rmt, rmtp))

			return -EFAULT;

	}



	return ret;

}