linux-kernel - Re: [v4.9-rc4] dvb-usb/cinergyT2 NULL pointer dereference

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Date:   Tue, 8 Nov 2016 10:42:03 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jörg Otte <jrg.otte@...il.com>,
        Patrick Boettcher <patrick.boettcher@...teo.de>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>
Subject: Re: [v4.9-rc4] dvb-usb/cinergyT2 NULL pointer dereference

On Sun, Nov 6, 2016 at 7:40 AM, Jörg Otte <jrg.otte@...il.com> wrote:
> Since v4.9-rc4 I get following crash in dvb-usb-cinergyT2 module.

Looks like it's commit 5ef8ed0e5608f ("[media] cinergyT2-core: don't
do DMA on stack"), which movced the DMA data array from the stack to
the "private" pointer. In the process it also added serialization in
the form of "data_mutex", but and now it oopses on that mutex because
the private pointer is NULL.

It looks like the "->private" pointer is allocated in dvb_usb_adapter_init()

cinergyt2_usb_probe ->
  dvb_usb_device_init ->
    dvb_usb_init() ->
      dvb_usb_adapter_init()

but the dvb_usb_init() function calls dvb_usb_device_power_ctrl()
(which calls the "power_ctrl" function, which is
cinergyt2_power_ctrl() for that drive) *before* it initializes the
private field.

Mauro, Patrick, could dvb_usb_adapter_init() be called earlier, perhaps?

                    Linus