[Nouveau] [PATCH v1] drm/nouveau/device: append a NUL-terminated character for the string which filled by strncpy()

[Nouveau] [PATCH v1] drm/nouveau/device: append a NUL-terminated character for the string which filled by strncpy()

[Luo Jiaxing]

Following warning is found when using W=1 to build kernel:

In function ‘nvkm_udevice_info’,
    inlined from ‘nvkm_udevice_mthd’ at drivers/gpu/drm/nouveau/nvkm/engine/device/user.c:195:10:
drivers/gpu/drm/nouveau/nvkm/engine/device/user.c:164:2: warning: ‘strncpy’ specified bound 16 equals destination size [-Wstringop-truncation]
  164 |  strncpy(args->v0.chip, device->chip->name, sizeof(args->v0.chip));
drivers/gpu/drm/nouveau/nvkm/engine/device/user.c:165:2: warning: ‘strncpy’ specified bound 64 equals destination size [-Wstringop-truncation]
  165 |  strncpy(args->v0.name, device->name, sizeof(args->v0.name));

The reason of this warning is strncpy() does not guarantee that the
destination buffer will be NUL terminated. If the length of source string
is bigger than number we set by third input parameter, only first [number]
of characters is copied to the destination, and no NUL-terminated is
automatically added. There are some potential risks.

Signed-off-by: Luo Jiaxing <luojiaxing@huawei.com>
---
 drivers/gpu/drm/nouveau/nvkm/engine/device/user.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c b/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
index fea9d8f..2a32fe0 100644
--- a/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
@@ -161,8 +161,10 @@ nvkm_udevice_info(struct nvkm_udevice *udev, void *data, u32 size)
 	if (imem && args->v0.ram_size > 0)
 		args->v0.ram_user = args->v0.ram_user - imem->reserved;
 
-	strncpy(args->v0.chip, device->chip->name, sizeof(args->v0.chip));
-	strncpy(args->v0.name, device->name, sizeof(args->v0.name));
+	strncpy(args->v0.chip, device->chip->name, sizeof(args->v0.chip) - 1);
+	args->v0.chip[sizeof(args->v0.chip) - 1] = '\0';
+	strncpy(args->v0.name, device->name, sizeof(args->v0.name) - 1);
+	args->v0.name[sizeof(args->v0.name) - 1] = '\0';
 	return 0;
 }
 
-- 
2.7.4

_______________________________________________
Nouveau mailing list
Nouveau@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/nouveau

Re: [Nouveau] [Linuxarm] [PATCH v1] drm/nouveau/device: append a NUL-terminated character for the string which filled by strncpy()

[Song Bao Hua (Barry Song)]

> -----Original Message-----
> From: Luo Jiaxing [mailto:luojiaxing@huawei.com]
> Sent: Friday, February 26, 2021 12:39 AM
> To: nouveau@lists.freedesktop.org; dri-devel@lists.freedesktop.org;
> bskeggs@redhat.com
> Cc: linux-kernel@vger.kernel.org; linuxarm@openeuler.org; luojiaxing
> <luojiaxing@huawei.com>
> Subject: [Linuxarm] [PATCH v1] drm/nouveau/device: append a NUL-terminated
> character for the string which filled by strncpy()
> 
> Following warning is found when using W=1 to build kernel:
> 
> In function ‘nvkm_udevice_info’,
>     inlined from ‘nvkm_udevice_mthd’ at
> drivers/gpu/drm/nouveau/nvkm/engine/device/user.c:195:10:
> drivers/gpu/drm/nouveau/nvkm/engine/device/user.c:164:2: warning: ‘strncpy’
> specified bound 16 equals destination size [-Wstringop-truncation]
>   164 |  strncpy(args->v0.chip, device->chip->name, sizeof(args->v0.chip));
> drivers/gpu/drm/nouveau/nvkm/engine/device/user.c:165:2: warning: ‘strncpy’
> specified bound 64 equals destination size [-Wstringop-truncation]
>   165 |  strncpy(args->v0.name, device->name, sizeof(args->v0.name));
> 
> The reason of this warning is strncpy() does not guarantee that the
> destination buffer will be NUL terminated. If the length of source string
> is bigger than number we set by third input parameter, only first [number]
> of characters is copied to the destination, and no NUL-terminated is
> automatically added. There are some potential risks.
> 
> Signed-off-by: Luo Jiaxing <luojiaxing@huawei.com>
> ---
>  drivers/gpu/drm/nouveau/nvkm/engine/device/user.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
> b/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
> index fea9d8f..2a32fe0 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
> @@ -161,8 +161,10 @@ nvkm_udevice_info(struct nvkm_udevice *udev, void *data,
> u32 size)
>  	if (imem && args->v0.ram_size > 0)
>  		args->v0.ram_user = args->v0.ram_user - imem->reserved;
> 
> -	strncpy(args->v0.chip, device->chip->name, sizeof(args->v0.chip));
> -	strncpy(args->v0.name, device->name, sizeof(args->v0.name));
> +	strncpy(args->v0.chip, device->chip->name, sizeof(args->v0.chip) - 1);
> +	args->v0.chip[sizeof(args->v0.chip) - 1] = '\0';
> +	strncpy(args->v0.name, device->name, sizeof(args->v0.name) - 1);
> +	args->v0.name[sizeof(args->v0.name) - 1] = '\0';


Isn't it better to use snprintf()?

>  	return 0;
>  }
> 
Thanks
Barry

_______________________________________________
Nouveau mailing list
Nouveau@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/nouveau

Re: [Nouveau] [Linuxarm] [PATCH v1] drm/nouveau/device: append a NUL-terminated character for the string which filled by strncpy()

[luojiaxing]

On 2021/2/26 9:01, Song Bao Hua (Barry Song) wrote:
>
>> -----Original Message-----
>> From: Luo Jiaxing [mailto:luojiaxing@huawei.com]
>> Sent: Friday, February 26, 2021 12:39 AM
>> To: nouveau@lists.freedesktop.org; dri-devel@lists.freedesktop.org;
>> bskeggs@redhat.com
>> Cc: linux-kernel@vger.kernel.org; linuxarm@openeuler.org; luojiaxing
>> <luojiaxing@huawei.com>
>> Subject: [Linuxarm] [PATCH v1] drm/nouveau/device: append a NUL-terminated
>> character for the string which filled by strncpy()
>>
>> Following warning is found when using W=1 to build kernel:
>>
>> In function ‘nvkm_udevice_info’,
>>      inlined from ‘nvkm_udevice_mthd’ at
>> drivers/gpu/drm/nouveau/nvkm/engine/device/user.c:195:10:
>> drivers/gpu/drm/nouveau/nvkm/engine/device/user.c:164:2: warning: ‘strncpy’
>> specified bound 16 equals destination size [-Wstringop-truncation]
>>    164 |  strncpy(args->v0.chip, device->chip->name, sizeof(args->v0.chip));
>> drivers/gpu/drm/nouveau/nvkm/engine/device/user.c:165:2: warning: ‘strncpy’
>> specified bound 64 equals destination size [-Wstringop-truncation]
>>    165 |  strncpy(args->v0.name, device->name, sizeof(args->v0.name));
>>
>> The reason of this warning is strncpy() does not guarantee that the
>> destination buffer will be NUL terminated. If the length of source string
>> is bigger than number we set by third input parameter, only first [number]
>> of characters is copied to the destination, and no NUL-terminated is
>> automatically added. There are some potential risks.
>>
>> Signed-off-by: Luo Jiaxing <luojiaxing@huawei.com>
>> ---
>>   drivers/gpu/drm/nouveau/nvkm/engine/device/user.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
>> b/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
>> index fea9d8f..2a32fe0 100644
>> --- a/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
>> +++ b/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
>> @@ -161,8 +161,10 @@ nvkm_udevice_info(struct nvkm_udevice *udev, void *data,
>> u32 size)
>>   	if (imem && args->v0.ram_size > 0)
>>   		args->v0.ram_user = args->v0.ram_user - imem->reserved;
>>
>> -	strncpy(args->v0.chip, device->chip->name, sizeof(args->v0.chip));
>> -	strncpy(args->v0.name, device->name, sizeof(args->v0.name));
>> +	strncpy(args->v0.chip, device->chip->name, sizeof(args->v0.chip) - 1);
>> +	args->v0.chip[sizeof(args->v0.chip) - 1] = '\0';
>> +	strncpy(args->v0.name, device->name, sizeof(args->v0.name) - 1);
>> +	args->v0.name[sizeof(args->v0.name) - 1] = '\0';
>
> Isn't it better to use snprintf()?


yes, you are right,  snprintf() is better. Most of drivers use 
snprintf() to format a string,

but still some examples in kernel that use it for copy.


I modify to code to the follow and I think it's the same with strncpy 
but more safety

diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c 
b/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
index fea9d8f..4bf65bb 100644
--- a/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
@@ -161,8 +161,8 @@ nvkm_udevice_info(struct nvkm_udevice *udev, void 
*data, u32 size)
         if (imem && args->v0.ram_size > 0)
                 args->v0.ram_user = args->v0.ram_user - imem->reserved;

-       strncpy(args->v0.chip, device->chip->name, sizeof(args->v0.chip));
-       strncpy(args->v0.name, device->name, sizeof(args->v0.name));
+       snprintf(args->v0.chip, sizeof(args->v0.chip), "%s", 
device->chip->name);
+       snprintf(args->v0.name, sizeof(args->v0.name), "%s", device->name);

Thanks

Jiaxing


>
>>   	return 0;
>>   }
>>
> Thanks
> Barry
>

_______________________________________________
Nouveau mailing list
Nouveau@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/nouveau