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compat: nanosleep: Clarify error handling

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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: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Thomas Gleixner 2014-09-06 12:18:07 +02:00
parent 40bea03959
commit 849151dd54
1 changed files with 21 additions and 3 deletions
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24
kernel/compat.c
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@ -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;
}