On Thu, Sep 21, 2023 at 05:41:46AM +0000, Justin Stitt wrote: > `strncpy` is deprecated for use on NUL-terminated destination strings [1]. > > Let's refactor this kcalloc() + strncpy() into a kmemdup_nul() which has > more obvious behavior and is less error prone. > > To avoid truncating the last byte supply `...length + 1` to > kmemdup_nul() as `element->string.length` does not account for the > trailing null as made obvious from it's definition (and associated > comment): > | u32 length; /* # of bytes in string, excluding trailing null */ > > ... this is precisely what the original kcalloc invocation did as well. > > 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@xxxxxxxxxxxxxxx > Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx> > --- > Changes in v3: > - refactor to use kmemdup_nul() (thanks Thomas and Kees) > - change commit msg to reflect ^ > - rebase onto 2cf0f71562387282 > - Link to v2: https://lore.kernel.org/r/20230919-strncpy-drivers-hwmon-acpi_power_meter-c-v2-1-8348432d6442@xxxxxxxxxx > > Changes in v2: > - use memcpy over strscpy (thanks Kees) > - Link to v1: https://lore.kernel.org/r/20230914-strncpy-drivers-hwmon-acpi_power_meter-c-v1-1-905297479fe8@xxxxxxxxxx > --- > drivers/hwmon/acpi_power_meter.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/drivers/hwmon/acpi_power_meter.c b/drivers/hwmon/acpi_power_meter.c > index fa28d447f0df..146c4f09c897 100644 > --- a/drivers/hwmon/acpi_power_meter.c > +++ b/drivers/hwmon/acpi_power_meter.c > @@ -796,14 +796,13 @@ static int read_capabilities(struct acpi_power_meter_resource *resource) > goto error; > } > > - *str = kcalloc(element->string.length + 1, sizeof(u8), > - GFP_KERNEL); > + *str = kmemdup_nul(element->string.pointer, element->string.length + 1, > + GFP_KERNEL); kmemdup_nul() already adds the "+ 1", so it's not needed here. For v4, please improve the Subject along the lines of "...: Replace open-coded kmemdup_nul" -Kees > if (!*str) { > res = -ENOMEM; > goto error; > } > > - strncpy(*str, element->string.pointer, element->string.length); > str++; > } > > > --- > base-commit: 2cf0f715623872823a72e451243bbf555d10d032 > change-id: 20230914-strncpy-drivers-hwmon-acpi_power_meter-c-c9f2d8053bef > > Best regards, > -- > Justin Stitt <justinstitt@xxxxxxxxxx> > -- Kees Cook
