RE: [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@xxxxxxxxxx]
> Sent: Friday, February 26, 2021 12:39 AM
> To: nouveau@xxxxxxxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx;
> bskeggs@xxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linuxarm@xxxxxxxxxxxxx; luojiaxing
> <luojiaxing@xxxxxxxxxx>
> 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@xxxxxxxxxx>
> ---
>  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