Code: static int snd_timer_user_tselect(struct file *file,
				  struct snd_timer_select __user *_tselect)
{
	struct snd_timer_user *tu;
	struct snd_timer_select tselect;
	char str[32];
 	int err = 0;
 
 	tu = file->private_data;
	mutex_lock(&tu->tread_sem);
 	if (tu->timeri) {
 		snd_timer_close(tu->timeri);
 		tu->timeri = NULL;
	}
	if (copy_from_user(&tselect, _tselect, sizeof(tselect))) {
		err = -EFAULT;
		goto __err;
	}
	sprintf(str, "application %i", current->pid);
	if (tselect.id.dev_class != SNDRV_TIMER_CLASS_SLAVE)
		tselect.id.dev_sclass = SNDRV_TIMER_SCLASS_APPLICATION;
	err = snd_timer_open(&tu->timeri, str, &tselect.id, current->pid);
	if (err < 0)
		goto __err;

	kfree(tu->queue);
	tu->queue = NULL;
	kfree(tu->tqueue);
	tu->tqueue = NULL;
	if (tu->tread) {
		tu->tqueue = kmalloc(tu->queue_size * sizeof(struct snd_timer_tread),
				     GFP_KERNEL);
		if (tu->tqueue == NULL)
			err = -ENOMEM;
	} else {
		tu->queue = kmalloc(tu->queue_size * sizeof(struct snd_timer_read),
				    GFP_KERNEL);
		if (tu->queue == NULL)
			err = -ENOMEM;
	}

      	if (err < 0) {
		snd_timer_close(tu->timeri);
      		tu->timeri = NULL;
      	} else {
		tu->timeri->flags |= SNDRV_TIMER_IFLG_FAST;
		tu->timeri->callback = tu->tread
			? snd_timer_user_tinterrupt : snd_timer_user_interrupt;
		tu->timeri->ccallback = snd_timer_user_ccallback;
		tu->timeri->callback_data = (void *)tu;
 	}
 
       __err:
      	mutex_unlock(&tu->tread_sem);
 	return err;
 }

Commit Message: ALSA: timer: Fix race among timer ioctls

ALSA timer ioctls have an open race and this may lead to a
use-after-free of timer instance object.  A simplistic fix is to make
each ioctl exclusive.  We have already tread_sem for controlling the
tread, and extend this as a global mutex to be applied to each ioctl.

The downside is, of course, the worse concurrency.  But these ioctls
aren't to be parallel accessible, in anyway, so it should be fine to
serialize there.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
CWE ID: CWE-362
static int snd_timer_user_tselect(struct file *file,
				  struct snd_timer_select __user *_tselect)
{
	struct snd_timer_user *tu;
	struct snd_timer_select tselect;
	char str[32];
 	int err = 0;
 
 	tu = file->private_data;
 	if (tu->timeri) {
 		snd_timer_close(tu->timeri);
 		tu->timeri = NULL;
	}
	if (copy_from_user(&tselect, _tselect, sizeof(tselect))) {
		err = -EFAULT;
		goto __err;
	}
	sprintf(str, "application %i", current->pid);
	if (tselect.id.dev_class != SNDRV_TIMER_CLASS_SLAVE)
		tselect.id.dev_sclass = SNDRV_TIMER_SCLASS_APPLICATION;
	err = snd_timer_open(&tu->timeri, str, &tselect.id, current->pid);
	if (err < 0)
		goto __err;

	kfree(tu->queue);
	tu->queue = NULL;
	kfree(tu->tqueue);
	tu->tqueue = NULL;
	if (tu->tread) {
		tu->tqueue = kmalloc(tu->queue_size * sizeof(struct snd_timer_tread),
				     GFP_KERNEL);
		if (tu->tqueue == NULL)
			err = -ENOMEM;
	} else {
		tu->queue = kmalloc(tu->queue_size * sizeof(struct snd_timer_read),
				    GFP_KERNEL);
		if (tu->queue == NULL)
			err = -ENOMEM;
	}

      	if (err < 0) {
		snd_timer_close(tu->timeri);
      		tu->timeri = NULL;
      	} else {
		tu->timeri->flags |= SNDRV_TIMER_IFLG_FAST;
		tu->timeri->callback = tu->tread
			? snd_timer_user_tinterrupt : snd_timer_user_interrupt;
		tu->timeri->ccallback = snd_timer_user_ccallback;
		tu->timeri->callback_data = (void *)tu;
 	}
 
       __err:
 	return err;
 }
