[PATCH v4] EDAC/mc_sysfs: refactor deprecated strncpy

[PATCH v4] EDAC/mc_sysfs: refactor deprecated strncpy

[Justin Stitt]

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

We've already calculated bounds, possible truncation with '\0' or '\n'
and manually NUL-terminated. The situation is now just a literal byte
copy from one buffer to another, let's treat it as such and use a less
ambiguous interface in memcpy.

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>
---
Changes in v4:
- prefer memcpy to strscpy (thanks Kees)
- Link to v3: https://lore.kernel.org/r/20230913-strncpy-drivers-edac-edac_mc_sysfs-c-v3-1-38c1db7d207f@google.com

Changes in v3:
- prefer strscpy to strscpy_pad (thanks Tony)
- Link to v2: https://lore.kernel.org/r/20230913-strncpy-drivers-edac-edac_mc_sysfs-c-v2-1-2d2e6bd43642@google.com

Changes in v2:
- included refactor of another strncpy in same file
- Link to v1: https://lore.kernel.org/r/20230913-strncpy-drivers-edac-edac_mc_sysfs-c-v1-1-d232891b05b0@google.com
---
Note: build-tested only.
---
 drivers/edac/edac_mc_sysfs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/edac/edac_mc_sysfs.c b/drivers/edac/edac_mc_sysfs.c
index 15f63452a9be..5116873c3330 100644
--- a/drivers/edac/edac_mc_sysfs.c
+++ b/drivers/edac/edac_mc_sysfs.c
@@ -229,7 +229,7 @@ static ssize_t channel_dimm_label_store(struct device *dev,
 	if (copy_count == 0 || copy_count >= sizeof(rank->dimm->label))
 		return -EINVAL;
 
-	strncpy(rank->dimm->label, data, copy_count);
+	memcpy(rank->dimm->label, data, copy_count);
 	rank->dimm->label[copy_count] = '\0';
 
 	return count;
@@ -535,7 +535,7 @@ static ssize_t dimmdev_label_store(struct device *dev,
 	if (copy_count == 0 || copy_count >= sizeof(dimm->label))
 		return -EINVAL;
 
-	strncpy(dimm->label, data, copy_count);
+	memcpy(dimm->label, data, copy_count);
 	dimm->label[copy_count] = '\0';
 
 	return count;

---
base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
change-id: 20230913-strncpy-drivers-edac-edac_mc_sysfs-c-e619b00124a3

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

Re: [PATCH v4] EDAC/mc_sysfs: refactor deprecated strncpy

[Kees Cook]

On Mon, Sep 18, 2023 at 07:47:29AM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We've already calculated bounds, possible truncation with '\0' or '\n'
> and manually NUL-terminated. The situation is now just a literal byte
> copy from one buffer to another, let's treat it as such and use a less
> ambiguous interface in memcpy.
> 
> 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>

Yeah, I think this looks good now. If a v5 is needed, a tiny improvement
would be to update the Subject: to "...: replace strncpy with memcpy".

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

-- 
Kees Cook

Re: [PATCH v4] EDAC/mc_sysfs: refactor deprecated strncpy

[Kees Cook]

On Mon, 18 Sep 2023 07:47:29 +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We've already calculated bounds, possible truncation with '\0' or '\n'
> and manually NUL-terminated. The situation is now just a literal byte
> copy from one buffer to another, let's treat it as such and use a less
> ambiguous interface in memcpy.
> 
> [...]

Applied to for-next/hardening, thanks! (Subject updated...)

Take care,

-- 
Kees Cook