[PATCH 01/13] timer: Convert schedule_timeout() to use from_timer()

[Kees Cook]

In preparation for unconditionally passing the struct timer_list pointer to
all timer callbacks, switch to using the new from_timer() helper and passing
the timer pointer explicitly. Since this special timer is on the stack, it
needs to have a wrapper structure to carry state once .data is eliminated.

Cc: John Stultz <john.stu...@linaro.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Stephen Boyd <sb...@codeaurora.org>
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 include/linux/timer.h |  8 ++++++++
 kernel/time/timer.c   | 26 +++++++++++++++++++-------
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/include/linux/timer.h b/include/linux/timer.h
index 6383c528b148..5ef5c9e41a09 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -179,6 +179,14 @@ static inline void timer_setup(struct timer_list *timer,
                      (TIMER_DATA_TYPE)timer, flags);
 }
 
+static inline void timer_setup_on_stack(struct timer_list *timer,
+                              void (*callback)(struct timer_list *),
+                              unsigned int flags)
+{
+       __setup_timer_on_stack(timer, (TIMER_FUNC_TYPE)callback,
+                              (TIMER_DATA_TYPE)timer, flags);
+}
+
 #define from_timer(var, callback_timer, timer_fieldname) \
        container_of(callback_timer, typeof(*var), timer_fieldname)
 
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index f2674a056c26..38613ced2324 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1668,9 +1668,20 @@ void run_local_timers(void)
        raise_softirq(TIMER_SOFTIRQ);
 }
 
-static void process_timeout(unsigned long __data)
+/*
+ * Since schedule_timeout()'s timer is defined on the stack, it must store
+ * the target task on the stack as well.
+ */
+struct process_timer {
+       struct timer_list timer;
+       struct task_struct *task;
+};
+
+static void process_timeout(struct timer_list *t)
 {
-       wake_up_process((struct task_struct *)__data);
+       struct process_timer *timeout = from_timer(timeout, t, timer);
+
+       wake_up_process(timeout->task);
 }
 
 /**
@@ -1704,7 +1715,7 @@ static void process_timeout(unsigned long __data)
  */
 signed long __sched schedule_timeout(signed long timeout)
 {
-       struct timer_list timer;
+       struct process_timer timer;
        unsigned long expire;
 
        switch (timeout)
@@ -1738,13 +1749,14 @@ signed long __sched schedule_timeout(signed long 
timeout)
 
        expire = timeout + jiffies;
 
-       setup_timer_on_stack(&timer, process_timeout, (unsigned long)current);
-       __mod_timer(&timer, expire, false);
+       timer.task = current;
+       timer_setup_on_stack(&timer.timer, process_timeout, 0);
+       __mod_timer(&timer.timer, expire, false);
        schedule();
-       del_singleshot_timer_sync(&timer);
+       del_singleshot_timer_sync(&timer.timer);
 
        /* Remove the timer from the object tracker */
-       destroy_timer_on_stack(&timer);
+       destroy_timer_on_stack(&timer.timer);
 
        timeout = expire - jiffies;
 
-- 
2.7.4