On 2021/2/26 9:01, Song Bao Hua (Barry Song) wrote:
-----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()?
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
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