s390/3270: fix use after free of tty3270_screen structure

The deactivation and freeing of the tty view of the 3270 device
can race with a tty3270_update invocation via the update timer.
To fix this move the del_timer_sync call for the update timer from
tty3270_free_view to tty3270_free prior to the tty3270_free_screen
call.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 2 insertions, 5 deletions

diff --git a/drivers/s390/char/tty3270.c b/drivers/s390/char/tty3270.c
index 3f4ca4e09a4c..07cf182c18f9 100644
--- a/drivers/s390/char/tty3270.c
+++ b/drivers/s390/char/tty3270.c
@@ -125,10 +125,7 @@ static void tty3270_resize_work(struct work_struct *work);
  */
 static void tty3270_set_timer(struct tty3270 *tp, int expires)
 {
-        if (expires == 0)
-                del_timer(&tp->timer);
-        else
-                mod_timer(&tp->timer, jiffies + expires);
+        mod_timer(&tp->timer, jiffies + expires);
 }
 
 /*
@@ -744,7 +741,6 @@ tty3270_free_view(struct tty3270 *tp)
 {
         int pages;
 
-        del_timer_sync(&tp->timer);
         kbd_free(tp->kbd);
         raw3270_request_free(tp->kreset);
         raw3270_request_free(tp->read);
@@ -877,6 +873,7 @@ tty3270_free(struct raw3270_view *view)
 {
         struct tty3270 *tp = container_of(view, struct tty3270, view);
 
+        del_timer_sync(&tp->timer);
         tty3270_free_screen(tp->screen, tp->view.rows);
         tty3270_free_view(tp);
 }