* Re: [PATCH] drm/nouveau/nvif: refactor deprecated strncpy
2023-09-14 21:30 [PATCH] drm/nouveau/nvif: refactor deprecated strncpy Justin Stitt
@ 2023-09-15 4:54 ` Kees Cook
2023-09-15 17:34 ` Lyude Paul
1 sibling, 0 replies; 3+ messages in thread
From: Kees Cook @ 2023-09-15 4:54 UTC (permalink / raw)
To: Justin Stitt
Cc: Ben Skeggs, Karol Herbst, Lyude Paul, David Airlie, Daniel Vetter,
dri-devel, nouveau, linux-kernel, linux-hardening
On Thu, Sep 14, 2023 at 09:30:37PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated and as such we should prefer more robust and
> less ambiguous string interfaces.
>
> A suitable replacement is `strscpy_pad` due to the fact that it
> guarantees NUL-termination on the destination buffer whilst also
> maintaining the NUL-padding behavior that `strncpy` provides. I am not
> sure whether NUL-padding is strictly needed but I see in
> `nvif_object_ctor()` args is memcpy'd elsewhere so I figured we'd keep
> the same functionality.
>
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
> Note: build-tested only.
> ---
> drivers/gpu/drm/nouveau/nvif/client.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nvif/client.c b/drivers/gpu/drm/nouveau/nvif/client.c
> index a3264a0e933a..3a27245f467f 100644
> --- a/drivers/gpu/drm/nouveau/nvif/client.c
> +++ b/drivers/gpu/drm/nouveau/nvif/client.c
> @@ -69,7 +69,7 @@ nvif_client_ctor(struct nvif_client *parent, const char *name, u64 device,
> } nop = {};
> int ret;
>
> - strncpy(args.name, name, sizeof(args.name));
> + strscpy_pad(args.name, name, sizeof(args.name));
> ret = nvif_object_ctor(parent != client ? &parent->object : NULL,
> name ? name : "nvifClient", 0,
> NVIF_CLASS_CLIENT, &args, sizeof(args),
Right, I see the memcpy too:
nvif_object_ctor(struct nvif_object *parent, const char *name, u32 handle,
s32 oclass, void *data, u32 size, struct nvif_object *object)
{
...
memcpy(args->new.data, data, size);
However, "args" is already zeroed:
struct nvif_client_v0 args = { .device = device };
So there's no need for _pad(). However, I couldn't immediatley see
why args.name must be %NUL terminated. It's ultimately passed through
an ioctl:
return client->driver->ioctl(client->object.priv, data, size, hack);
But I did find it...
args is:
struct nvif_client_v0 {
...
char name[32];
};
And "name" only ever comes through nvif_client_ctor(), which all end up
via here, using "cli":
struct nouveau_cli {
...
char name[32];
...
snprintf(cli->name, sizeof(cli->name), "%s", sname);
...
ret = nvif_client_ctor(&drm->master.base, cli->name, device,
&cli->base);
So we'll always be %NUL terminated.
Therefore, yes, conversion looks good:
Reviewed-by: Kees Cook <keescook@chromium.org>
Thanks!
-Kees
>
> ---
> base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
> change-id: 20230914-strncpy-drivers-gpu-drm-nouveau-nvif-client-c-82b023c36953
>
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
>
--
Kees Cook
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] drm/nouveau/nvif: refactor deprecated strncpy
2023-09-14 21:30 [PATCH] drm/nouveau/nvif: refactor deprecated strncpy Justin Stitt
2023-09-15 4:54 ` Kees Cook
@ 2023-09-15 17:34 ` Lyude Paul
1 sibling, 0 replies; 3+ messages in thread
From: Lyude Paul @ 2023-09-15 17:34 UTC (permalink / raw)
To: Justin Stitt, Ben Skeggs, Karol Herbst, David Airlie,
Daniel Vetter
Cc: dri-devel, nouveau, linux-kernel, linux-hardening
Reviewed-by: Lyude Paul <lyude@redhat.com>
Will push this and your other patches in just a moment
On Thu, 2023-09-14 at 21:30 +0000, Justin Stitt wrote:
> `strncpy` is deprecated and as such we should prefer more robust and
> less ambiguous string interfaces.
>
> A suitable replacement is `strscpy_pad` due to the fact that it
> guarantees NUL-termination on the destination buffer whilst also
> maintaining the NUL-padding behavior that `strncpy` provides. I am not
> sure whether NUL-padding is strictly needed but I see in
> `nvif_object_ctor()` args is memcpy'd elsewhere so I figured we'd keep
> the same functionality.
>
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
> Note: build-tested only.
> ---
> drivers/gpu/drm/nouveau/nvif/client.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nvif/client.c b/drivers/gpu/drm/nouveau/nvif/client.c
> index a3264a0e933a..3a27245f467f 100644
> --- a/drivers/gpu/drm/nouveau/nvif/client.c
> +++ b/drivers/gpu/drm/nouveau/nvif/client.c
> @@ -69,7 +69,7 @@ nvif_client_ctor(struct nvif_client *parent, const char *name, u64 device,
> } nop = {};
> int ret;
>
> - strncpy(args.name, name, sizeof(args.name));
> + strscpy_pad(args.name, name, sizeof(args.name));
> ret = nvif_object_ctor(parent != client ? &parent->object : NULL,
> name ? name : "nvifClient", 0,
> NVIF_CLASS_CLIENT, &args, sizeof(args),
>
> ---
> base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
> change-id: 20230914-strncpy-drivers-gpu-drm-nouveau-nvif-client-c-82b023c36953
>
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
>
--
Cheers,
Lyude Paul (she/her)
Software Engineer at Red Hat
^ permalink raw reply [flat|nested] 3+ messages in thread