Messages in this thread | | | Date | Sun, 14 Jan 2018 20:37:14 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH] time: POSIX CPU timers: Ensure that variable is initialized |
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On Mon, 8 Jan 2018, Max R. P. Grossmann wrote:
> If cpu_timer_sample_group returns -EINVAL, it will not have written into > *sample. Checking for cpu_timer_sample_group's return value precludes the > potential use of an uninitialized value of now in the following block. > Given an invalid clock_idx, the previous code could otherwise overwrite > *oldval in an undefined manner. This is now prevented. We also exploit > short-circuiting of && to sample the timer only if the result will > actually be used to update *oldval.
Sure the explanation makes sense, though you should have mentioned that _ALL_ current users call this function with a valid clockid.
I'll amend the changelog.
> Signed-off-by: Max R. P. Grossmann <m@max.pm> > --- > kernel/time/posix-cpu-timers.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c > index 1f27887aa194..e54638be6e19 100644 > --- a/kernel/time/posix-cpu-timers.c > +++ b/kernel/time/posix-cpu-timers.c > @@ -1189,9 +1189,8 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx, > u64 now; > > WARN_ON_ONCE(clock_idx == CPUCLOCK_SCHED); > - cpu_timer_sample_group(clock_idx, tsk, &now); > > - if (oldval) { > + if (oldval && cpu_timer_sample_group(clock_idx, tsk, &now) != -EINVAL) { > /* > * We are setting itimer. The *oldval is absolute and we update > * it to be relative, *newval argument is relative and we update > -- > 2.15.1 > >
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