linux-kernel - Re: [PATCH] r8152: Allocate interrupt buffer as part of struct r8152

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Date:   Tue, 31 Jan 2017 14:53:47 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Guenter Roeck <linux@...ck-us.net>
cc:     "David S . Miller" <davem@...emloft.net>,
        <linux-usb@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Hayes Wang <hayeswang@...ltek.com>
Subject: Re: [PATCH] r8152: Allocate interrupt buffer as part of struct r8152

On Tue, 31 Jan 2017, Guenter Roeck wrote:

> When unloading the r8152 driver using the 'unbind' sysfs attribute
> in a system with KASAN enabled, the following error message is seen
> on a regular basis.

...

> The two-byte allocation in conjunction with code analysis suggests that
> the interrupt buffer has been overwritten. Added instrumentation in the
> driver shows that the interrupt handler is called after RTL8152_UNPLUG
> was set, and that this event is associated with the error message above.
> This suggests that there are situations where the interrupt buffer is used
> after it has been freed.
> 
> To avoid the problem, allocate the interrupt buffer as part of struct
> r8152.
> 
> Cc: Hayes Wang <hayeswang@...ltek.com>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
> The problem is seen in chromeos-4.4, but there is not reason to believe
> that it does not occur with the upstream kernel. It is still seen in
> chromeos-4.4 after all patches from upstream and linux-next have been
> applied to the driver.
> 
> While relatively simple, I am not really convinced that this is the best
> (or even an acceptable) solution for this problem. I am open to suggestions
> for a better fix.

The proper approach is to keep the allocation as it is, but _before_
deallocating the buffer, make sure that the interrupt buffer won't be
accessed any more.  This may involve calling usb_kill_urb(), or
synchronize_irq(), or something similar.

Alan Stern