futex: Fix futex_waitv() hrtimer debug object leak on kcalloc error

In a scenario where kcalloc() fails to allocate memory, the futex_waitv
system call immediately returns -ENOMEM without invoking
destroy_hrtimer_on_stack(). When CONFIG_DEBUG_OBJECTS_TIMERS=y, this
results in leaking a timer debug object.

Fixes: bf69bad ("futex: Implement sys_futex_waitv()")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: stable@vger.kernel.org
Cc: stable@vger.kernel.org # v5.16+
Link: https://lore.kernel.org/r/20221214222008.200393-1-mathieu.desnoyers@efficios.com

kernel/futex/syscalls.c

@@ -286,19 +286,22 @@ SYSCALL_DEFINE5(futex_waitv, struct futex_waitv __user *, waiters,
 	}
 
 	futexv = kcalloc(nr_futexes, sizeof(*futexv), GFP_KERNEL);
-	if (!futexv)
-		return -ENOMEM;
+	if (!futexv) {
+		ret = -ENOMEM;
+		goto destroy_timer;
+	}
 
 	ret = futex_parse_waitv(futexv, waiters, nr_futexes);
 	if (!ret)
 		ret = futex_wait_multiple(futexv, nr_futexes, timeout ? &to : NULL);
 
+	kfree(futexv);
+
+destroy_timer:
 	if (timeout) {
 		hrtimer_cancel(&to.timer);
 		destroy_hrtimer_on_stack(&to.timer);
 	}
-
-	kfree(futexv);
 	return ret;
 }