linux-kernel - Re: [PATCH][media-next] media: ddbridge: avoid out-of-bounds write on array demod_in

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Date:   Tue, 8 May 2018 11:39:56 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Daniel Scheller <d.scheller.oss@...il.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][media-next] media: ddbridge: avoid out-of-bounds write on
 array demod_in_use

On 08/05/18 11:38, Daniel Scheller wrote:
> Hi Colin,
> 
> Am Tue,  8 May 2018 00:08:42 +0100
> schrieb Colin King <colin.king@...onical.com>:
> 
>> From: Colin Ian King <colin.king@...onical.com>
>>
>> In function stop there is a check to see if state->demod is a stopped
>> value of 0xff, however, later on, array demod_in_use is indexed with
>> this value causing an out-of-bounds write error.  Avoid this by only
>> writing to array demod_in_use if state->demod is not set to the stopped
>> sentinal value for this specific corner case.  Also, replace the magic
>> value 0xff with DEMOD_STOPPED to make code more readable.
>>
>> Detected by CoverityScan, CID#1468550 ("Out-of-bounds write")
>>
>> Fixes: daeeb1319e6f ("media: ddbridge: initial support for MCI-based MaxSX8 cards")
>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>> ---
>>  drivers/media/pci/ddbridge/ddbridge-mci.c | 11 +++++++----
>>  1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/media/pci/ddbridge/ddbridge-mci.c b/drivers/media/pci/ddbridge/ddbridge-mci.c
>> index a85ff3e6b919..1f5ed53c8d35 100644
>> --- a/drivers/media/pci/ddbridge/ddbridge-mci.c
>> +++ b/drivers/media/pci/ddbridge/ddbridge-mci.c
>> @@ -20,6 +20,8 @@
>>  #include "ddbridge-io.h"
>>  #include "ddbridge-mci.h"
>>  
>> +#define DEMOD_STOPPED	(0xff)
>> +
>>  static LIST_HEAD(mci_list);
>>  
>>  static const u32 MCLK = (1550000000 / 12);
>> @@ -193,7 +195,7 @@ static int stop(struct dvb_frontend *fe)
>>  	u32 input = state->tuner;
>>  
>>  	memset(&cmd, 0, sizeof(cmd));
>> -	if (state->demod != 0xff) {
>> +	if (state->demod != DEMOD_STOPPED) {
>>  		cmd.command = MCI_CMD_STOP;
>>  		cmd.demod = state->demod;
>>  		mci_cmd(state, &cmd, NULL);
>> @@ -209,10 +211,11 @@ static int stop(struct dvb_frontend *fe)
>>  	state->base->tuner_use_count[input]--;
>>  	if (!state->base->tuner_use_count[input])
>>  		mci_set_tuner(fe, input, 0);
>> -	state->base->demod_in_use[state->demod] = 0;
>> +	if (state->demod != DEMOD_STOPPED)
>> +		state->base->demod_in_use[state->demod] = 0;
>>  	state->base->used_ldpc_bitrate[state->nr] = 0;
>> -	state->demod = 0xff;
>> -	state->base->assigned_demod[state->nr] = 0xff;
>> +	state->demod = DEMOD_STOPPED;
>> +	state->base->assigned_demod[state->nr] = DEMOD_STOPPED;
>>  	state->base->iq_mode = 0;
>>  	mutex_unlock(&state->base->tuner_lock);
>>  	state->started = 0;
> 
> Thanks for the patch, or - better - pointing this out. While it's
> unlikely this will ever be an issue, I'm fine with changing the code
> like that, but I'd prefer to change it a bit differently (ie.
> DEMOD_STOPPED should be DEMOD_UNUSED, and I'd add defines for max.
> tuners and use/compare against them).

Sounds like a good idea.

> 
> I'll send out a different patch that will cover the potential
> coverityscan problem throughout the end of the week.

Great. Thanks!

> 
> Best regards,
> Daniel Scheller
>