[PATCH][media-next] media: ddbridge: avoid out-of-bounds write on array demod_in_use

[PATCH][media-next] media: ddbridge: avoid out-of-bounds write on array demod_in_use

[Colin King]

From: Colin Ian King <colin.king@canonical.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@canonical.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;
-- 
2.17.0

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

[Daniel Scheller]

Hi Colin,

Am Tue,  8 May 2018 00:08:42 +0100
schrieb Colin King <colin.king@canonical.com>:

> From: Colin Ian King <colin.king@canonical.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@canonical.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).

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

Best regards,
Daniel Scheller
-- 
https://github.com/herrnst

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

[Colin Ian King]

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@canonical.com>:
> 
>> From: Colin Ian King <colin.king@canonical.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@canonical.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
> 

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

[Daniel Scheller]

Hi Colin,

Am Tue, 8 May 2018 11:39:56 +0100
schrieb Colin Ian King <colin.king@canonical.com>:

> 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@canonical.com>:
> >   
> >> From: Colin Ian King <colin.king@canonical.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@canonical.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!

JFYI, patch sent as part of a few other fixes and up at linux-media
patchwork:

https://patchwork.linuxtv.org/patch/49403/

Best regards,
Daniel Scheller
-- 
https://github.com/herrnst