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Date:   Fri, 20 Oct 2023 19:46:11 +0000
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Message-ID: <20231020-strncpy-drivers-power-supply-surface_charger-c-v1-1-93ddbf668e10@google.com>
Subject: [PATCH] power: supply: surface-charger: replace deprecated strncpy
 with strscpy
From:   Justin Stitt <justinstitt@google.com>
To:     Maximilian Luz <luzmaximilian@gmail.com>,
        Sebastian Reichel <sre@kernel.org>
Cc:     linux-pm@vger.kernel.org, platform-driver-x86@vger.kernel.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] and as such we should prefer more robust and less ambiguous string
interfaces.

We expect ac->name to be NUL-terminated based on its usage with format
strings:

surface_charger.c:
190: ac->psy_desc.name = ac->name;

...

power_supply_core.c:
174: dev_dbg(&psy->dev, "%s: Found supply : %s\n",
175:   psy->desc->name, epsy->desc->name);

Moreover, NUL-padding is not required as ac is already zero-allocated
before being passed to spwr_ac_init():

surface_charger.c:
240: ac = devm_kzalloc(&sdev->dev, sizeof(*ac), GFP_KERNEL);
241: if (!ac)
242:   return -ENOMEM;
243:
244: spwr_ac_init(ac, sdev, p->registry, p->name);

... this means any future 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 for 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@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Note: build-tested only.

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

diff --git a/drivers/power/supply/surface_charger.c b/drivers/power/supply/surface_charger.c
index cabdd8da12d0..7a6c62d6f883 100644
--- a/drivers/power/supply/surface_charger.c
+++ b/drivers/power/supply/surface_charger.c
@@ -175,7 +175,7 @@ static void spwr_ac_init(struct spwr_ac_device *ac, struct ssam_device *sdev,
 			 struct ssam_event_registry registry, const char *name)
 {
 	mutex_init(&ac->lock);
-	strncpy(ac->name, name, ARRAY_SIZE(ac->name) - 1);
+	strscpy(ac->name, name, sizeof(ac->name));
 
 	ac->sdev = sdev;
 

---
base-commit: bb55d7f7f7445abcc8db50e6a65d4315e79f75c7
change-id: 20231020-strncpy-drivers-power-supply-surface_charger-c-466920fb1f48

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