[PATCH 4.16 07/26] posix-cpu-timers: Ensure set_process_cpu_timer is always evaluated

From: Greg Kroah-Hartman
Date: Wed Apr 25 2018 - 06:35:44 EST

4.16-stable review patch. If anyone has any objections, please let me know.


From: Laura Abbott <labbott@xxxxxxxxxx>

commit c3bca5d450b620dd3d36e14b5e1f43639fd47d6b upstream.

Commit a9445e47d897 ("posix-cpu-timers: Make set_process_cpu_timer()
more robust") moved the check into the 'if' statement. Unfortunately,
it did so on the right side of an && which means that it may get short
circuited and never evaluated. This is easily reproduced with:

$ cat loop.c
void main() {
struct rlimit res;
/* set the CPU time limit */
res.rlim_cur = 2;
res.rlim_max = 2;

while (1);

Which will hang forever instead of being killed. Fix this by pulling the
evaluation out of the if statement but checking the return value instead.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1568337
Fixes: a9445e47d897 ("posix-cpu-timers: Make set_process_cpu_timer() more robust")
Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: "Max R . P . Grossmann" <m@xxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20180417215742.2521-1-labbott@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

kernel/time/posix-cpu-timers.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1205,10 +1205,12 @@ void set_process_cpu_timer(struct task_s
u64 *newval, u64 *oldval)
u64 now;
+ int ret;

+ ret = cpu_timer_sample_group(clock_idx, tsk, &now);

- if (oldval && cpu_timer_sample_group(clock_idx, tsk, &now) != -EINVAL) {
+ if (oldval && ret != -EINVAL) {
* We are setting itimer. The *oldval is absolute and we update
* it to be relative, *newval argument is relative and we update