linux-kernel - Re: FW: FW: RE: Re: FW: RE: Re: Subject: [PATCH v3] USB:Core: BugFix: Proper handling of Race Condition when two USB class drivers try to call init_usb

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]

Date:   Fri, 3 Mar 2017 11:53:43 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Ajay Kaher <ajay.kaher@...sung.com>
cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        AMAN DEEP <aman.deep@...sung.com>,
        HEMANSHU SRIVASTAVA <hemanshu.s@...sung.com>
Subject: Re: FW: FW: RE: Re: FW: RE: Re: Subject: [PATCH v3] USB:Core: BugFix:
 Proper handling of Race Condition when two USB class drivers try to call
 init_usb_class simultaneously

On Fri, 3 Mar 2017, Ajay Kaher wrote:

> > usb_class->kref is not accessible outside the file.c
> > as usb_class is _static_ inside the file.c and
> > pointer of usb_class->kref is not passed anywhere.
> > 
> > Hence as you wanted, there are no references of usb_class->kref
> > other than taken by init_usb_class() and released by destroy_usb_class().
> 
> Verified the code again, I hope my last comments clarifed the things
> which came in your mind and helps you to accept the patch :)

Your main point is that usb_class->kref is accessed from only two
points, both of which are protected by the new mutex.  This means there
is no reason for the value to be a struct kref at all.  You should
change it to an int (and change its name).  Leaving it as a kref will
make readers wonder why it needs to be updated atomically.

Also, why does destroy_usb_class() have that "if (usb_class) "test?  
Isn't it true that usb_class can never be NULL there?

Alan Stern

> thanks,
> ajay kaher
>  
>  
> Signed-off-by: Ajay Kaher
>  
> ---
>  
>  drivers/usb/core/file.c |    6 ++++++
>  1 file changed, 6 insertions(+)
>  
> diff --git a/drivers/usb/core/file.c b/drivers/usb/core/file.c
> index 822ced9..a12d184 100644
> --- a/drivers/usb/core/file.c
> +++ b/drivers/usb/core/file.c
> @@ -27,6 +27,7 @@
>  #define MAX_USB_MINORS 256
>  static const struct file_operations *usb_minors[MAX_USB_MINORS];
>  static DECLARE_RWSEM(minor_rwsem);
> +static DEFINE_MUTEX(init_usb_class_mutex);
>  
>  static int usb_open(struct inode *inode, struct file *file)
>  {
> @@ -109,8 +110,10 @@ static void release_usb_class(struct kref *kref)
>  
>  static void destroy_usb_class(void)
>  {
> +       mutex_lock(&init_usb_class_mutex);
>         if (usb_class)
>                 kref_put(&usb_class->kref, release_usb_class);
> +       mutex_unlock(&init_usb_class_mutex);
>  }
>  
>  int usb_major_init(void)
> @@ -171,7 +174,10 @@ int usb_register_dev(struct usb_interface *intf,
>         if (intf->minor >= 0)
>                 return -EADDRINUSE;
>  
> +       mutex_lock(&init_usb_class_mutex);
>         retval = init_usb_class();
> +       mutex_unlock(&init_usb_class_mutex);
> +
>         if (retval)
>                 return retval;
>