2023-09-15 01:10:33

by Justin Stitt

Subject: [PATCH] drm/i915: refactor deprecated strncpy

`strncpy` is deprecated for use on NUL-terminated destination strings [1].

We should prefer more robust and less ambiguous string interfaces.

A suitable replacement is `strscpy` [2] due to the fact that it guarantees
NUL-termination on the destination buffer without unnecessarily NUL-padding.

`ctx` is zero allocated and as such strncpy's NUL-padding behavior was
strictly a performance hit which should now be resolved. It should be
noted, however, that performance is not critical in these selftests,
especially by these margins.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: [email protected]
Signed-off-by: Justin Stitt <[email protected]>
---
drivers/gpu/drm/i915/gem/selftests/mock_context.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/selftests/mock_context.c b/drivers/gpu/drm/i915/gem/selftests/mock_context.c
index 8ac6726ec16b..025b9c773b93 100644
--- a/drivers/gpu/drm/i915/gem/selftests/mock_context.c
+++ b/drivers/gpu/drm/i915/gem/selftests/mock_context.c
@@ -36,7 +36,7 @@ mock_context(struct drm_i915_private *i915,
if (name) {
struct i915_ppgtt *ppgtt;

- strncpy(ctx->name, name, sizeof(ctx->name) - 1);
+ strscpy(ctx->name, name, sizeof(ctx->name) - 1);

ppgtt = mock_ppgtt(i915, name);
if (!ppgtt)

---
base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
change-id: 20230914-strncpy-drivers-gpu-drm-i915-gem-selftests-mock_context-c-980c8ecc9142

Best regards,
--
Justin Stitt <[email protected]>

2023-09-15 06:06:16

by Kees Cook

Subject: Re: [PATCH] drm/i915: refactor deprecated strncpy

On Thu, Sep 14, 2023 at 09:14:07PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
>
> We should prefer more robust and less ambiguous string interfaces.
>
> A suitable replacement is `strscpy` [2] due to the fact that it guarantees
> NUL-termination on the destination buffer without unnecessarily NUL-padding.
>
> `ctx` is zero allocated and as such strncpy's NUL-padding behavior was
> strictly a performance hit which should now be resolved. It should be
> noted, however, that performance is not critical in these selftests,
> especially by these margins.
>
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: [email protected]
> Signed-off-by: Justin Stitt <[email protected]>
> ---
> drivers/gpu/drm/i915/gem/selftests/mock_context.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/selftests/mock_context.c b/drivers/gpu/drm/i915/gem/selftests/mock_context.c
> index 8ac6726ec16b..025b9c773b93 100644
> --- a/drivers/gpu/drm/i915/gem/selftests/mock_context.c
> +++ b/drivers/gpu/drm/i915/gem/selftests/mock_context.c
> @@ -36,7 +36,7 @@ mock_context(struct drm_i915_private *i915,
> if (name) {
> struct i915_ppgtt *ppgtt;
>
> - strncpy(ctx->name, name, sizeof(ctx->name) - 1);
> + strscpy(ctx->name, name, sizeof(ctx->name) - 1);

I'd expect the "- 1" to go away...

-Kees

>
> ppgtt = mock_ppgtt(i915, name);
> if (!ppgtt)
>
> ---
> base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
> change-id: 20230914-strncpy-drivers-gpu-drm-i915-gem-selftests-mock_context-c-980c8ecc9142
>
> Best regards,
> --
> Justin Stitt <[email protected]>
>

--
Kees Cook