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Date:   Thu, 14 Sep 2023 21:40:49 +0000
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Message-ID: <20230914-strncpy-drivers-gpu-drm-nouveau-nvkm-core-firmware-c-v1-1-3aeae46c032f@google.com>
Subject: [PATCH] drm/nouveau/core: refactor deprecated strncpy
From:   Justin Stitt <justinstitt@google.com>
To:     Ben Skeggs <bskeggs@redhat.com>, Karol Herbst <kherbst@redhat.com>,
        Lyude Paul <lyude@redhat.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>
Cc:     dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org,
        Justin Stitt <justinstitt@google.com>
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Precedence: bulk

`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.

There is likely no bug in the current implementation due to the safeguard:
| 	cname[sizeof(cname) - 1] = '\0';
... however we can provide simpler and easier to understand code using
the newer (and recommended) `strscpy` api.

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: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
 drivers/gpu/drm/nouveau/nvkm/core/firmware.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nvkm/core/firmware.c b/drivers/gpu/drm/nouveau/nvkm/core/firmware.c
index 91fb494d4009..374212da9e95 100644
--- a/drivers/gpu/drm/nouveau/nvkm/core/firmware.c
+++ b/drivers/gpu/drm/nouveau/nvkm/core/firmware.c
@@ -79,8 +79,7 @@ nvkm_firmware_get(const struct nvkm_subdev *subdev, const char *fwname, int ver,
 	int i;
 
 	/* Convert device name to lowercase */
-	strncpy(cname, device->chip->name, sizeof(cname));
-	cname[sizeof(cname) - 1] = '\0';
+	strscpy(cname, device->chip->name, sizeof(cname));
 	i = strlen(cname);
 	while (i) {
 		--i;

---
base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
change-id: 20230914-strncpy-drivers-gpu-drm-nouveau-nvkm-core-firmware-c-791223838b72

Best regards,
--
Justin Stitt <justinstitt@google.com>