linux-kernel - Re: [v3 PATCH] usb: create usb_debug

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87sgsv2n54.fsf@linux.intel.com>
Date:   Fri, 31 May 2019 08:44:55 +0300
From:   Felipe Balbi <felipe.balbi@...ux.intel.com>
To:     Chunfeng Yun <chunfeng.yun@...iatek.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-usb@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [v3 PATCH] usb: create usb_debug_root for gadget only


Hi,

Chunfeng Yun <chunfeng.yun@...iatek.com> writes:

> Hi Felipe,
> On Tue, 2019-05-28 at 11:11 +0300, Felipe Balbi wrote:
>> Hi,
>> 
>> Chunfeng Yun <chunfeng.yun@...iatek.com> writes:
>> > diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
>> > index 7fcb9f782931..88b3ee03a12d 100644
>> > --- a/drivers/usb/core/usb.c
>> > +++ b/drivers/usb/core/usb.c
>> > @@ -1190,7 +1190,7 @@ EXPORT_SYMBOL_GPL(usb_debug_root);
>> >  
>> >  static void usb_debugfs_init(void)
>> >  {
>> > -	usb_debug_root = debugfs_create_dir("usb", NULL);
>> > +	usb_debug_root = debugfs_create_dir(USB_DEBUG_ROOT_NAME, NULL);
>> >  	debugfs_create_file("devices", 0444, usb_debug_root, NULL,
>> >  			    &usbfs_devices_fops);
>> >  }
>> 
>> might be a better idea to move this to usb common. Then have a function
>> which can be called by both host and gadget to maybe create the
>> directory:
>> 
>> static struct dentry *usb_debug_root;
>> 
>> struct dentry *usb_debugfs_init(void)
>> {
>> 	if (!usb_debug_root)
>>         	usb_debug_root = debugfs_create_dir("usb", NULL);
>> 
>> 	return usb_debug_root;
>> }
>> 
>> 
>> Then usb core would be updated to something like:
>> 
>> static void usb_core_debugfs_init(void)
>> {
>> 	struct dentry *root = usb_debugfs_init();
>> 
>> 	debugfs_create_file("devices", 0444, root, NULL, &usbfs_devices_fops);
>> }
>> 
> I find a problem when move usb_debugfs_init() and usb_debugfs_cleanup()
> into usb common, it's easy to create "usb" directory, but difficult to
> cleanup it:
>
> common/common.c
>
> struct dentry *usb_debugfs_init(void)
> {
>     if (!usb_debug_root)
>         usb_debug_root = debugfs_create_dir("usb", NULL);
>
>     return usb_debug_root;
> }
>
> void usb_debugfs_cleanup(void)
> {
>     debugfs_remove_recursive(usb_debug_root);
>     usb_debug_root = NULL;
> }
>
> core/usb.c
>
> static void usb_core_debugfs_init(void)
> {
>     struct dentry *root = usb_debugfs_init();
>
>     debugfs_create_file("devices", 0444, root, NULL,
> &usbfs_devices_fops);
> }
>
> static int __init usb_init(void)
> {
>     ...
>     usb_core_debugfs_init();
>     ...
> }
>
> static void __exit usb_exit(void)
> {
>     ...
>     usb_debugfs_cleanup();
>     // will be error, gadget may use it.
>     ...
> }
>
> gadget/udc/core.c
>
> static int __init usb_udc_init(void)
> {
>     ...
>     usb_debugfs_init();
>     ...
> }
>
> static void __exit usb_udc_exit(void)
> {
>     ...
>     usb_debugfs_cleanup();
>     // can't cleanup in fact, usb core may use it.
> }
>
> How to handle this case? introduce a reference count? do you have any
> suggestion?

I guess a simple refcount is the way to go:

struct dentry *usb_debugfs_init(void)
{
	if (!usb_debug_root)
		usb_debug_root = debugfs_create_dir("usb", NULL);

	usb_debug_root_refcnt++;
	return usb_debug_root;
}

void usb_debugfs_cleanup(void)
{
	if (!(--usb_debug_root_refcnt)) {
		debugfs_remove_recursive(usb_debug_root);
		usb_debug_root = NULL;
	}
}

Or something along those lines

-- 
balbi