linux-kernel - Re: [PATCH] video: exynos: fix build warning and bad pointer deref in dp driver

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Message-ID: <CAOesGMjH3wwR1k-jurXm4vED8peTLStaQGmQ4Wx4M-bza9Jrcw@mail.gmail.com>
Date:	Mon, 9 Apr 2012 07:05:31 -0700
From:	Olof Johansson <olof@...om.net>
To:	Jingoo Han <jg1.han@...sung.com>
Cc:	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] video: exynos: fix build warning and bad pointer deref in
 dp driver

On Mon, Apr 9, 2012 at 1:46 AM, Jingoo Han <jg1.han@...sung.com> wrote:
>> -----Original Message-----
>> From: Olof Johansson [mailto:olof@...om.net]
>> Sent: Monday, April 09, 2012 1:16 PM
>>
>> I'm not 100% sure if the fix for 'adjust_request' is correct, since
>> it's uncertain what the original intent was. But it's so clearly an
>> uninitialized pointer dereference that my resolution seems to make sense.
>>
>> drivers/video/exynos/exynos_dp_core.c: In function 'exynos_dp_set_link_train':
>> drivers/video/exynos/exynos_dp_core.c:521:21: warning: 'adjust_request' may be used uninitialized in
>> this function [-Wuninitialized]
>> drivers/video/exynos/exynos_dp_core.c:481:6: note: 'adjust_request' was declared here
>> drivers/video/exynos/exynos_dp_core.c:529:18: warning: 'reg' may be used uninitialized in this function
>> [-Wuninitialized]
>> drivers/video/exynos/exynos_dp_core.c:395:6: note: 'reg' was declared here
>>
>> Signed-off-by: Olof Johansson <olof@...om.net>
>> ---
>>  drivers/video/exynos/exynos_dp_core.c |   23 +++++++++--------------
>>  1 file changed, 9 insertions(+), 14 deletions(-)
>>
>> diff --git a/drivers/video/exynos/exynos_dp_core.c b/drivers/video/exynos/exynos_dp_core.c
>> index 2a4481c..8973e18 100644
>> --- a/drivers/video/exynos/exynos_dp_core.c
>> +++ b/drivers/video/exynos/exynos_dp_core.c
>> @@ -392,24 +392,19 @@ static unsigned int exynos_dp_get_lane_link_training(
>>                               struct exynos_dp_device *dp,
>>                               int lane)
>>  {
>> -     u32 reg;
>> -
>>       switch (lane) {
>>       case 0:
>> -             reg = exynos_dp_get_lane0_link_training(dp);
>> -             break;
>> +             return exynos_dp_get_lane0_link_training(dp);
>>       case 1:
>> -             reg = exynos_dp_get_lane1_link_training(dp);
>> -             break;
>> +             return exynos_dp_get_lane1_link_training(dp);
>>       case 2:
>> -             reg = exynos_dp_get_lane2_link_training(dp);
>> -             break;
>> +             return exynos_dp_get_lane2_link_training(dp);
>>       case 3:
>> -             reg = exynos_dp_get_lane3_link_training(dp);
>> -             break;
>> +             return exynos_dp_get_lane3_link_training(dp);
>>       }
>
> I don't like multi return.

In a small helper function like this there's nothing wrong with it.
Larger functions? Sure.

Adding a default in the switch didn't seem like an improvement to me.
But I'll leave it up to you.

>>
>> -     return reg;
>> +     WARN_ON(1);
>> +     return 0;
>>  }
>>
>>  static void exynos_dp_reduce_link_rate(struct exynos_dp_device *dp)
>> @@ -489,13 +484,13 @@ static int exynos_dp_process_clock_recovery(struct exynos_dp_device *dp)
>>                               6, link_status);
>>       lane_count = dp->link_train.lane_count;
>>
>> +     adjust_request = link_status + (DPCD_ADDR_ADJUST_REQUEST_LANE0_1
>> +                                     - DPCD_ADDR_LANE0_1_STATUS);
>> +
>
> It makes the problem. adjust_request will be different.
>
> OK, I understand what you want to do.
> I will send the version 2 patch which is simpler.
>
> Thank you for sending the patch.

Ok, thanks. As I said, I'm not sure what your intent with the second
(else) code path was.


-Olof
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