[PATCH] drivers/video: Fix -Wstringop-truncation in hdmi.c

[PATCH] drivers/video: Fix -Wstringop-truncation in hdmi.c

[Thomas Zimmermann]

Trying to copy into the string fields with strncpy() gives a warning from
gcc. Both fields are part of a packed HDMI header and do not require a
terminating \0 character.

../drivers/video/hdmi.c: In function 'hdmi_spd_infoframe_init':
../drivers/video/hdmi.c:230:2: warning: 'strncpy' specified bound 8 equals destination size [-Wstringop-truncation]
  230 |  strncpy(frame->vendor, vendor, sizeof(frame->vendor));
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../drivers/video/hdmi.c:231:2: warning: 'strncpy' specified bound 16 equals destination size [-Wstringop-truncation]
  231 |  strncpy(frame->product, product, sizeof(frame->product));
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Just use memcpy() instead.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/video/hdmi.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c
index b7a1d6fae90d..1e4cb63d0d11 100644
--- a/drivers/video/hdmi.c
+++ b/drivers/video/hdmi.c
@@ -221,14 +221,18 @@ EXPORT_SYMBOL(hdmi_avi_infoframe_pack);
 int hdmi_spd_infoframe_init(struct hdmi_spd_infoframe *frame,
 			    const char *vendor, const char *product)
 {
+	size_t len;
+
 	memset(frame, 0, sizeof(*frame));
 
 	frame->type = HDMI_INFOFRAME_TYPE_SPD;
 	frame->version = 1;
 	frame->length = HDMI_SPD_INFOFRAME_SIZE;
 
-	strncpy(frame->vendor, vendor, sizeof(frame->vendor));
-	strncpy(frame->product, product, sizeof(frame->product));
+	len = strlen(vendor);
+	memcpy(frame->vendor, vendor, min(len, sizeof(frame->vendor)));
+	len = strlen(product);
+	memcpy(frame->product, product, min(len, sizeof(frame->product)));
 
 	return 0;
 }
-- 
2.28.0

Re: [PATCH] drivers/video: Fix -Wstringop-truncation in hdmi.c

[Laurent Pinchart]

Hi Thomas,

Thank you for the patch.

On Wed, Oct 21, 2020 at 02:12:41PM +0200, Thomas Zimmermann wrote:
> Trying to copy into the string fields with strncpy() gives a warning from
> gcc. Both fields are part of a packed HDMI header and do not require a
> terminating \0 character.
> 
> ../drivers/video/hdmi.c: In function 'hdmi_spd_infoframe_init':
> ../drivers/video/hdmi.c:230:2: warning: 'strncpy' specified bound 8 equals destination size [-Wstringop-truncation]
>   230 |  strncpy(frame->vendor, vendor, sizeof(frame->vendor));
>       |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../drivers/video/hdmi.c:231:2: warning: 'strncpy' specified bound 16 equals destination size [-Wstringop-truncation]
>   231 |  strncpy(frame->product, product, sizeof(frame->product));
>       |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Just use memcpy() instead.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
>  drivers/video/hdmi.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c
> index b7a1d6fae90d..1e4cb63d0d11 100644
> --- a/drivers/video/hdmi.c
> +++ b/drivers/video/hdmi.c
> @@ -221,14 +221,18 @@ EXPORT_SYMBOL(hdmi_avi_infoframe_pack);
>  int hdmi_spd_infoframe_init(struct hdmi_spd_infoframe *frame,
>  			    const char *vendor, const char *product)
>  {
> +	size_t len;
> +
>  	memset(frame, 0, sizeof(*frame));
>  
>  	frame->type = HDMI_INFOFRAME_TYPE_SPD;
>  	frame->version = 1;
>  	frame->length = HDMI_SPD_INFOFRAME_SIZE;
>  
> -	strncpy(frame->vendor, vendor, sizeof(frame->vendor));
> -	strncpy(frame->product, product, sizeof(frame->product));
> +	len = strlen(vendor);
> +	memcpy(frame->vendor, vendor, min(len, sizeof(frame->vendor)));
> +	len = strlen(product);
> +	memcpy(frame->product, product, min(len, sizeof(frame->product)));

As this seems to be a legitimate use of strncpy(), isn't there a way to
silence the warning without requiring this additional runtime complexity
?

>  
>  	return 0;
>  }

-- 
Regards,

Laurent Pinchart

Re: [PATCH] drivers/video: Fix -Wstringop-truncation in hdmi.c

[Thomas Zimmermann]

Hi

On 22.10.20 01:06, Laurent Pinchart wrote:
> Hi Thomas,
> 
> Thank you for the patch.
> 
> On Wed, Oct 21, 2020 at 02:12:41PM +0200, Thomas Zimmermann wrote:
>> Trying to copy into the string fields with strncpy() gives a warning from
>> gcc. Both fields are part of a packed HDMI header and do not require a
>> terminating \0 character.
>>
>> ../drivers/video/hdmi.c: In function 'hdmi_spd_infoframe_init':
>> ../drivers/video/hdmi.c:230:2: warning: 'strncpy' specified bound 8 equals destination size [-Wstringop-truncation]
>>   230 |  strncpy(frame->vendor, vendor, sizeof(frame->vendor));
>>       |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> ../drivers/video/hdmi.c:231:2: warning: 'strncpy' specified bound 16 equals destination size [-Wstringop-truncation]
>>   231 |  strncpy(frame->product, product, sizeof(frame->product));
>>       |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> Just use memcpy() instead.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>> ---
>>  drivers/video/hdmi.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c
>> index b7a1d6fae90d..1e4cb63d0d11 100644
>> --- a/drivers/video/hdmi.c
>> +++ b/drivers/video/hdmi.c
>> @@ -221,14 +221,18 @@ EXPORT_SYMBOL(hdmi_avi_infoframe_pack);
>>  int hdmi_spd_infoframe_init(struct hdmi_spd_infoframe *frame,
>>  			    const char *vendor, const char *product)
>>  {
>> +	size_t len;
>> +
>>  	memset(frame, 0, sizeof(*frame));
>>  
>>  	frame->type = HDMI_INFOFRAME_TYPE_SPD;
>>  	frame->version = 1;
>>  	frame->length = HDMI_SPD_INFOFRAME_SIZE;
>>  
>> -	strncpy(frame->vendor, vendor, sizeof(frame->vendor));
>> -	strncpy(frame->product, product, sizeof(frame->product));
>> +	len = strlen(vendor);
>> +	memcpy(frame->vendor, vendor, min(len, sizeof(frame->vendor)));
>> +	len = strlen(product);
>> +	memcpy(frame->product, product, min(len, sizeof(frame->product)));
> 
> As this seems to be a legitimate use of strncpy(), isn't there a way to
> silence the warning without requiring this additional runtime complexity
> ?

Yes, the original code this correct. I looked through include/string.h
if there's better string function, but none fits. Most of them
0-terminate the output string.

The only simple fix seems to be to set gcc's -Wno-stringop-truncation
here. I'd expect that would be an even less preferable change.

Best regards
Thomas

> 
>>  
>>  	return 0;
>>  }
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

Re: [PATCH] drivers/video: Fix -Wstringop-truncation in hdmi.c

[Sam Ravnborg]

On Wed, Oct 21, 2020 at 02:12:41PM +0200, Thomas Zimmermann wrote:
> Trying to copy into the string fields with strncpy() gives a warning from
> gcc. Both fields are part of a packed HDMI header and do not require a
> terminating \0 character.
> 
> ../drivers/video/hdmi.c: In function 'hdmi_spd_infoframe_init':
> ../drivers/video/hdmi.c:230:2: warning: 'strncpy' specified bound 8 equals destination size [-Wstringop-truncation]
>   230 |  strncpy(frame->vendor, vendor, sizeof(frame->vendor));
>       |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../drivers/video/hdmi.c:231:2: warning: 'strncpy' specified bound 16 equals destination size [-Wstringop-truncation]
>   231 |  strncpy(frame->product, product, sizeof(frame->product));
>       |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Just use memcpy() instead.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
I assume vendor is guaranteed to be 0-termindated.
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>

> ---
>  drivers/video/hdmi.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c
> index b7a1d6fae90d..1e4cb63d0d11 100644
> --- a/drivers/video/hdmi.c
> +++ b/drivers/video/hdmi.c
> @@ -221,14 +221,18 @@ EXPORT_SYMBOL(hdmi_avi_infoframe_pack);
>  int hdmi_spd_infoframe_init(struct hdmi_spd_infoframe *frame,
>  			    const char *vendor, const char *product)
>  {
> +	size_t len;
> +
>  	memset(frame, 0, sizeof(*frame));
>  
>  	frame->type = HDMI_INFOFRAME_TYPE_SPD;
>  	frame->version = 1;
>  	frame->length = HDMI_SPD_INFOFRAME_SIZE;
>  
> -	strncpy(frame->vendor, vendor, sizeof(frame->vendor));
> -	strncpy(frame->product, product, sizeof(frame->product));
> +	len = strlen(vendor);
> +	memcpy(frame->vendor, vendor, min(len, sizeof(frame->vendor)));
> +	len = strlen(product);
> +	memcpy(frame->product, product, min(len, sizeof(frame->product)));
>  
>  	return 0;
>  }
> -- 
> 2.28.0
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: [PATCH] drivers/video: Fix -Wstringop-truncation in hdmi.c

[Thomas Zimmermann]

[-- Attachment #1.1.1: Type: text/plain, Size: 2726 bytes --]

Hi

Am 01.11.20 um 10:50 schrieb Sam Ravnborg:
> On Wed, Oct 21, 2020 at 02:12:41PM +0200, Thomas Zimmermann wrote:
>> Trying to copy into the string fields with strncpy() gives a warning from
>> gcc. Both fields are part of a packed HDMI header and do not require a
>> terminating \0 character.
>>
>> ../drivers/video/hdmi.c: In function 'hdmi_spd_infoframe_init':
>> ../drivers/video/hdmi.c:230:2: warning: 'strncpy' specified bound 8 equals destination size [-Wstringop-truncation]
>>   230 |  strncpy(frame->vendor, vendor, sizeof(frame->vendor));
>>       |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> ../drivers/video/hdmi.c:231:2: warning: 'strncpy' specified bound 16 equals destination size [-Wstringop-truncation]
>>   231 |  strncpy(frame->product, product, sizeof(frame->product));
>>       |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> Just use memcpy() instead.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> I assume vendor is guaranteed to be 0-termindated.

It's a fixed-length field in the protocol. There's similar code in
radeon IIRC. So it would be nice to disable the warning in these cases.
But that's probably to much fiddling.

> Reviewed-by: Sam Ravnborg <sam@ravnborg.org>

Thanks.

Best regards
Thomas

> 
>> ---
>>  drivers/video/hdmi.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c
>> index b7a1d6fae90d..1e4cb63d0d11 100644
>> --- a/drivers/video/hdmi.c
>> +++ b/drivers/video/hdmi.c
>> @@ -221,14 +221,18 @@ EXPORT_SYMBOL(hdmi_avi_infoframe_pack);
>>  int hdmi_spd_infoframe_init(struct hdmi_spd_infoframe *frame,
>>  			    const char *vendor, const char *product)
>>  {
>> +	size_t len;
>> +
>>  	memset(frame, 0, sizeof(*frame));
>>  
>>  	frame->type = HDMI_INFOFRAME_TYPE_SPD;
>>  	frame->version = 1;
>>  	frame->length = HDMI_SPD_INFOFRAME_SIZE;
>>  
>> -	strncpy(frame->vendor, vendor, sizeof(frame->vendor));
>> -	strncpy(frame->product, product, sizeof(frame->product));
>> +	len = strlen(vendor);
>> +	memcpy(frame->vendor, vendor, min(len, sizeof(frame->vendor)));
>> +	len = strlen(product);
>> +	memcpy(frame->product, product, min(len, sizeof(frame->product)));
>>  
>>  	return 0;
>>  }
>> -- 
>> 2.28.0
>>
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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