From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
commit eedeb787ebb53de5c5dcf7b7b39d01bf1b0f037d upstream.
Tetsuo-San noted that commit f5d39b020809 ("freezer,sched: Rewrite
core freezer logic") broke call_usermodehelper_exec() for the KILLABLE
case.
Specifically it was missed that the second, unconditional,
wait_for_completion() was not optional and ensures the on-stack
completion is unused before going out-of-scope.
Fixes: f5d39b020809 ("freezer,sched: Rewrite core freezer logic")
Reported-by: syzbot+6cd18e123583550cf469@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Debugged-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/Y90ar35uKQoUrLEK@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/umh.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)
diff --git a/kernel/umh.c b/kernel/umh.c
index 850631518665..fbf872c624cb 100644
--- a/kernel/umh.c
+++ b/kernel/umh.c
@@ -438,21 +438,27 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
if (wait == UMH_NO_WAIT) /* task has freed sub_info */
goto unlock;
- if (wait & UMH_KILLABLE)
- state |= TASK_KILLABLE;
-
if (wait & UMH_FREEZABLE)
state |= TASK_FREEZABLE;
- retval = wait_for_completion_state(&done, state);
- if (!retval)
- goto wait_done;
-
if (wait & UMH_KILLABLE) {
+ retval = wait_for_completion_state(&done, state | TASK_KILLABLE);
+ if (!retval)
+ goto wait_done;
+
/* umh_complete() will see NULL and free sub_info */
if (xchg(&sub_info->complete, NULL))
goto unlock;
+
+ /*
+ * fallthrough; in case of -ERESTARTSYS now do uninterruptible
+ * wait_for_completion_state(). Since umh_complete() shall call
+ * complete() in a moment if xchg() above returned NULL, this
+ * uninterruptible wait_for_completion_state() will not block
+ * SIGKILL'ed processes for long.
+ */
}
+ wait_for_completion_state(&done, state);
wait_done:
retval = sub_info->retval;
--
2.39.1
