linux-hardening - [PATCH] platform/surface: aggregator: replace deprecated strncpy with strscpy

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Message-ID: <20231020-strncpy-drivers-power-supply-surface_battery-c-v1-1-cabaea50e667@google.com>
Date: Fri, 20 Oct 2023 19:35:43 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Maximilian Luz <luzmaximilian@...il.com>, Sebastian Reichel <sre@...nel.org>
Cc: linux-pm@...r.kernel.org, platform-driver-x86@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, 
	Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] platform/surface: aggregator: replace deprecated strncpy with strscpy

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

We expect bat->name to be NUL-terminated based on its usage with
strcmp():

power_supply_core.c:
445: return strcmp(psy->desc->name, name) == 0;

... and also by the manual `... - 1` for the length argument of the
original strncpy() invocation.

Furthermore, no NUL-padding is needed as bat is zero-allocated before
calling spwr_battery_init():
826: bat = devm_kzalloc(&sdev->dev, sizeof(*bat), GFP_KERNEL);
827: if (!bat)
828:   return -ENOMEM;
829:
830: spwr_battery_init(bat, sdev, p->registry, p->name);

... this means any further NUL-byte assignments (like the ones that
strncpy() does) are redundant.

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

Let's also opt to use the more idiomatic strscpy() usage of:
(dest, src, sizeof(dest)).

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@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/power/supply/surface_battery.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/power/supply/surface_battery.c b/drivers/power/supply/surface_battery.c
index 19d2f8834e56..196d290dc596 100644
--- a/drivers/power/supply/surface_battery.c
+++ b/drivers/power/supply/surface_battery.c
@@ -722,7 +722,7 @@ static void spwr_battery_init(struct spwr_battery_device *bat, struct ssam_devic
 			      struct ssam_event_registry registry, const char *name)
 {
 	mutex_init(&bat->lock);
-	strncpy(bat->name, name, ARRAY_SIZE(bat->name) - 1);
+	strscpy(bat->name, name, sizeof(bat->name));
 
 	bat->sdev = sdev;
 

---
base-commit: bb55d7f7f7445abcc8db50e6a65d4315e79f75c7
change-id: 20231020-strncpy-drivers-power-supply-surface_battery-c-b0c84b05ac28

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