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: [email protected]
Signed-off-by: Justin Stitt <[email protected]>
---
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 <[email protected]>
Fixed the subject line in [v2].
On Fri, Oct 20, 2023 at 12:35 PM Justin Stitt <[email protected]> wrote:
>
> 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: [email protected]
> Signed-off-by: Justin Stitt <[email protected]>
> ---
> 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 <[email protected]>
>
[v2]: https://lore.kernel.org/r/20231020-strncpy-drivers-power-supply-surface_battery-c-v2-1-29ed16b2caf1@google.com
Thanks
Justin