linux-kernel - Re: [PATCH] [media] davinci/dm644x: work around ccdc_update_raw

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Date:   Tue, 27 Jun 2017 15:43:45 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
CC:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        linux-media <linux-media@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] [media] davinci/dm644x: work around
 ccdc_update_raw_params trainwreck

On Tuesday 20 June 2017 06:36 PM, Lad, Prabhakar wrote:
> Hi Arnd,
> 
> Thanks for the patch.
> 
> On Fri, Jun 9, 2017 at 10:36 PM, Arnd Bergmann <arnd@...db.de> wrote:
>> Now that the davinci drivers can be enabled in compile tests on other
>> architectures, I ran into this warning on a 64-bit build:
>>
>> drivers/media/platform/davinci/dm644x_ccdc.c: In function 'ccdc_update_raw_params':
>> drivers/media/platform/davinci/dm644x_ccdc.c:279:7: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>>
>> While that looks fairly harmless (it would be fine on 32-bit), it was
>> just the tip of the iceberg:
>>
>> - The function constantly mixes up pointers and phys_addr_t numbers
>> - This is part of a 'VPFE_CMD_S_CCDC_RAW_PARAMS' ioctl command that is
>>   described as an 'experimental ioctl that will change in future kernels',
>>   but if we have users that probably won't happen.
>> - The code to allocate the table never gets called after we copy_from_user
>>   the user input over the kernel settings, and then compare them
>>   for inequality.
>> - We then go on to use an address provided by user space as both the
>>   __user pointer for input and pass it through phys_to_virt to come up
>>   with a kernel pointer to copy the data to. This looks like a trivially
>>   exploitable root hole.
>>
>> This patch disables all the obviously broken code, by zeroing out the
>> sensitive data provided by user space. I also fix the type confusion
>> here. If we think the ioctl has no stable users, we could consider
>> just removing it instead.
>>
> I suspect there shouldn’t  be possible users of this IOCTL, better of  removing
> the IOCTL itself.
> 
> Sekhar your call, as the latest PSP releases for 644x use the media
> controller framework.

I do not have any personal experience with anyone using this support
with latest kernels. I too am okay with removing the broken support.

Since the header file that defines the ioctl is not in include/uapi/*, I
guess it cannot be considered stable userspace ABI? Also, there are
enough warnings about instability thrown in the comments surrounding the
ioctl in include/media/davinci/vpfe_capture.h.

Thanks,
Sekhar