On Fri, Sep 22, 2023 at 11:49:14AM +0000, Justin Stitt 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.
>
> `buf` is used in this context as a data buffer with 64 bytes of memory
> to be occupied by capi_manufakturer.
>
> We see the caller capi20_get_manufacturer() passes data.manufacturer as
> its `buf` argument which is then later passed over to user space. Due to
> this, let's keep the NUL-padding that strncpy provided by using
> strscpy_pad so as to not leak any stack data.
> | cdev->errcode = capi20_get_manufacturer(data.contr, data.manufacturer);
> | if (cdev->errcode)
> | return -EIO;
> |
> | if (copy_to_user(argp, data.manufacturer,
> | sizeof(data.manufacturer)))
> | return -EFAULT;
Yup, strongly agreed: this needs the padding. I actually wonder if a
follow-up patch might be a good idea here, just for robustness:
capi_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct capidev *cdev = file->private_data;
- capi_ioctl_struct data;
+ capi_ioctl_struct data = { };
>
> Perhaps this would also be a good instance to use `strtomem_pad` for but
> in my testing the compiler was not able to determine the size of `buf`
> -- even with all the hints.
>
> 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 <justinst...@google.com>
Reviewed-by: Kees Cook <keesc...@chromium.org>
--
Kees Cook
