mISDN: fix the races with timers going off just as they are deleted

timer callback in timerdev.c both accesses struct mISDNtimer it's
called for *and* moves it to dev->expired.  We need del_timer_sync(),
or we risk kfree() freeing it right under dev_expire_timer() *and*
dev->expired getting corrupted.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 12 insertions, 2 deletions

diff --git a/drivers/isdn/mISDN/timerdev.c b/drivers/isdn/mISDN/timerdev.c
index 1094667d8f31..5a1a5cadc766 100644
--- a/drivers/isdn/mISDN/timerdev.c
+++ b/drivers/isdn/mISDN/timerdev.c
@@ -72,14 +72,24 @@ static int
 mISDN_close(struct inode *ino, struct file *filep)
 {
         struct mISDNtimerdev    *dev = filep->private_data;
+        struct list_head        *list = &dev->pending;
         struct mISDNtimer       *timer, *next;
 
         if (*debug & DEBUG_TIMER)
                 printk(KERN_DEBUG "%s(%p,%p)\n", __func__, ino, filep);
-        list_for_each_entry_safe(timer, next, &dev->pending, list) {
-                del_timer(&timer->tl);
+
+        spin_lock_irq(&dev->lock);
+        while (!list_empty(list)) {
+                timer = list_first_entry(list, struct mISDNtimer, list);
+                spin_unlock_irq(&dev->lock);
+                del_timer_sync(&timer->tl);
+                spin_lock_irq(&dev->lock);
+                /* it might have been moved to ->expired */
+                list_del(&timer->list);
                 kfree(timer);
         }
+        spin_unlock_irq(&dev->lock);
+
         list_for_each_entry_safe(timer, next, &dev->expired, list) {
                 kfree(timer);
         }