Re: dvb shared datastructure bug?

[Marcel Siegert]

On Tuesday 13 February 2007, Arjan van de Ven wrote:
> Hi,
> 
> while working on the last pieces of the file_ops constantification, DVB
> is the small village in France that is holding the Romans at bay... but
> I think I found the final flaw in it now: 
> 
>        *pdvbdev = dvbdev = kmalloc(sizeof(struct dvb_device), GFP_KERNEL);
> 
>         if (!dvbdev) {
>                 mutex_unlock(&dvbdev_register_lock);
>                 return -ENOMEM;
>         }
> 
>         memcpy(dvbdev, template, sizeof(struct dvb_device));
>         dvbdev->type = type;
>         dvbdev->id = id;
>         dvbdev->adapter = adap;
>         dvbdev->priv = priv;
> 
>         dvbdev->fops->owner = adap->module;
> 
> 
> this is the place in DVB that is writing to a struct file_operations.
> But as with almost all such cases in the kernel, this one is buggy:
> While the code nicely copies a template dvbdev, that template only has a
> pointer to a *shared* fops struct, the copy doesn't help that. So this
> code is overwriting the fops owner field for ALL active devices, not
> just the ones the copy of the template is for....
> 
> I'm lost in the maze of this part of DVB (it seems to have some magic
> potion to resist me) but I was hoping some of the local citizens could
> take a look at this buglet...
> 
> Greetings,
>     Arjan van de Ven

hi arjan,
thanks for pointing out this issue.

attached find a patch that fixes the problem.

@mauro - please pull changeset a7ac92d208fe
   dvbdev: fix illegal re-usage of fileoperations struct

from  http://www.linuxtv.org/hg/~mws/v4l-dvb-fixtree

for upstream to kernel. thanks.

best regards 
marcel
diff -r 667e84e2e762 linux/drivers/media/dvb/dvb-core/dvbdev.c
--- a/linux/drivers/media/dvb/dvb-core/dvbdev.c	Tue Feb 13 07:00:55 2007 -0200
+++ b/linux/drivers/media/dvb/dvb-core/dvbdev.c	Tue Feb 13 12:00:13 2007 +0100
@@ -211,12 +211,14 @@ int dvb_register_device(struct dvb_adapt
 			const struct dvb_device *template, void *priv, int type)
 {
 	struct dvb_device *dvbdev;
+	struct file_operations *dvbdevfops;
+
 	int id;
 
 	if (mutex_lock_interruptible(&dvbdev_register_lock))
 		return -ERESTARTSYS;
 
-	if ((id = dvbdev_get_free_id (adap, type)) < 0) {
+	if ((id = dvbdev_get_free_id (adap, type)) < 0){
 		mutex_unlock(&dvbdev_register_lock);
 		*pdvbdev = NULL;
 		printk ("%s: could get find free device id...\n", __FUNCTION__);
@@ -225,7 +227,15 @@ int dvb_register_device(struct dvb_adapt
 
 	*pdvbdev = dvbdev = kmalloc(sizeof(struct dvb_device), GFP_KERNEL);
 
-	if (!dvbdev) {
+	if (!dvbdev){
+		mutex_unlock(&dvbdev_register_lock);
+		return -ENOMEM;
+	}
+
+	dvbdevfops = kzalloc(sizeof(struct file_operations), GFP_KERNEL);
+
+	if (!dvbdevfops){
+		kfree (dvbdev);
 		mutex_unlock(&dvbdev_register_lock);
 		return -ENOMEM;
 	}
@@ -235,7 +245,7 @@ int dvb_register_device(struct dvb_adapt
 	dvbdev->id = id;
 	dvbdev->adapter = adap;
 	dvbdev->priv = priv;
-
+	dvbdev->fops = dvbdevfops;
 	dvbdev->fops->owner = adap->module;
 
 	list_add_tail (&dvbdev->list_head, &adap->device_list);
@@ -263,6 +273,7 @@ void dvb_unregister_device(struct dvb_de
 					dvbdev->type, dvbdev->id)));
 
 	list_del (&dvbdev->list_head);
+	kfree (dvbdev->fops);
 	kfree (dvbdev);
 }
 EXPORT_SYMBOL(dvb_unregister_device);

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