[media] ir-lirc-codec: let lirc_dev handle the lirc_buffer

ir_lirc_register() currently creates its own lirc_buffer before
passing the lirc_driver to lirc_register_driver().

When a module is later unloaded, ir_lirc_unregister() gets called
which performs a call to lirc_unregister_driver() and then free():s
the lirc_buffer.

The problem is that:

a) there can still be a userspace app holding an open lirc fd
   when lirc_unregister_driver() returns; and

b) the lirc_buffer contains "wait_queue_head_t wait_poll" which
   is potentially used as long as any userspace app is still around.

The result is an oops which can be triggered quite easily by a
userspace app monitoring its lirc fd using epoll() and not closing
the fd promptly on device removal.

The minimalistic fix is to let lirc_dev create the lirc_buffer since
lirc_dev will then also free the buffer once it believes it is safe to
do so.

Signed-off-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/rc/ir-lirc-codec.c

@@ -354,7 +354,6 @@ static const struct file_operations lirc_fops = {
 static int ir_lirc_register(struct rc_dev *dev)
 {
 	struct lirc_driver *drv;
-	struct lirc_buffer *rbuf;
 	int rc = -ENOMEM;
 	unsigned long features = 0;
 
@@ -362,19 +361,12 @@ static int ir_lirc_register(struct rc_dev *dev)
 	if (!drv)
 		return rc;
 
-	rbuf = kzalloc(sizeof(struct lirc_buffer), GFP_KERNEL);
-	if (!rbuf)
-		goto rbuf_alloc_failed;
-
-	rc = lirc_buffer_init(rbuf, sizeof(int), LIRCBUF_SIZE);
-	if (rc)
-		goto rbuf_init_failed;
-
 	if (dev->driver_type != RC_DRIVER_IR_RAW_TX) {
 		features |= LIRC_CAN_REC_MODE2;
 		if (dev->rx_resolution)
 			features |= LIRC_CAN_GET_REC_RESOLUTION;
 	}
+
 	if (dev->tx_ir) {
 		features |= LIRC_CAN_SEND_PULSE;
 		if (dev->s_tx_mask)
@@ -403,10 +395,12 @@ static int ir_lirc_register(struct rc_dev *dev)
 	drv->minor = -1;
 	drv->features = features;
 	drv->data = &dev->raw->lirc;
-	drv->rbuf = rbuf;
+	drv->rbuf = NULL;
 	drv->set_use_inc = &ir_lirc_open;
 	drv->set_use_dec = &ir_lirc_close;
 	drv->code_length = sizeof(struct ir_raw_event) * 8;
+	drv->chunk_size = sizeof(int);
+	drv->buffer_size = LIRCBUF_SIZE;
 	drv->fops = &lirc_fops;
 	drv->dev = &dev->dev;
 	drv->rdev = dev;
@@ -415,19 +409,15 @@ static int ir_lirc_register(struct rc_dev *dev)
 	drv->minor = lirc_register_driver(drv);
 	if (drv->minor < 0) {
 		rc = -ENODEV;
-		goto lirc_register_failed;
+		goto out;
 	}
 
 	dev->raw->lirc.drv = drv;
 	dev->raw->lirc.dev = dev;
 	return 0;
 
-lirc_register_failed:
-rbuf_init_failed:
-	kfree(rbuf);
-rbuf_alloc_failed:
+out:
 	kfree(drv);
-
 	return rc;
 }
 
@@ -436,9 +426,8 @@ static int ir_lirc_unregister(struct rc_dev *dev)
 	struct lirc_codec *lirc = &dev->raw->lirc;
 
 	lirc_unregister_driver(lirc->drv->minor);
-	lirc_buffer_free(lirc->drv->rbuf);
-	kfree(lirc->drv->rbuf);
 	kfree(lirc->drv);
+	lirc->drv = NULL;
 
 	return 0;
 }

drivers/media/rc/lirc_dev.c

@@ -52,6 +52,7 @@ struct irctl {
 
 	struct mutex irctl_lock;
 	struct lirc_buffer *buf;
+	bool buf_internal;
 	unsigned int chunk_size;
 
 	struct device dev;
@@ -83,7 +84,7 @@ static void lirc_release(struct device *ld)
 
 	put_device(ir->dev.parent);
 
-	if (ir->buf != ir->d.rbuf) {
+	if (ir->buf_internal) {
 		lirc_buffer_free(ir->buf);
 		kfree(ir->buf);
 	}
@@ -198,6 +199,7 @@ static int lirc_allocate_buffer(struct irctl *ir)
 
 	if (d->rbuf) {
 		ir->buf = d->rbuf;
+		ir->buf_internal = false;
 	} else {
 		ir->buf = kmalloc(sizeof(struct lirc_buffer), GFP_KERNEL);
 		if (!ir->buf) {
@@ -208,8 +210,11 @@ static int lirc_allocate_buffer(struct irctl *ir)
 		err = lirc_buffer_init(ir->buf, chunk_size, buffer_size);
 		if (err) {
 			kfree(ir->buf);
+			ir->buf = NULL;
 			goto out;
 		}
+
+		ir->buf_internal = true;
 	}
 	ir->chunk_size = ir->buf->chunk_size;
 
@@ -362,6 +367,12 @@ int lirc_register_driver(struct lirc_driver *d)
 		err = lirc_allocate_buffer(irctls[minor]);
 		if (err)
 			lirc_unregister_driver(minor);
+		else
+			/*
+			 * This is kind of a hack but ir-lirc-codec needs
+			 * access to the buffer that lirc_dev allocated.
+			 */
+			d->rbuf = irctls[minor]->buf;
 	}
 
 	return err ? err : minor;