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SubjectRe: [PATCH] wmi: avoid a double-fetch issue in wmi_ioctl
On Tue, Dec 25, 2018 at 9:37 PM Kangjie Lu <kjlu@umn.edu> wrote:
>
> buf->length is first copied in from user space and security-checked. The
> second copy issued by copy_from_user copies it again. The data in user
> space may have been modified by malicious users.

So, we already did a check and copied not more than we would expect.

> filter_callback()
> further uses the potentially modified data.

How?

> The fix avoids the
> double-fetch that overwrites buf->length.

NAK.

> Signed-off-by: Kangjie Lu <kjlu@umn.edu>
> ---
> drivers/platform/x86/wmi.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
> index bea35be68706..93cab9a70ad7 100644
> --- a/drivers/platform/x86/wmi.c
> +++ b/drivers/platform/x86/wmi.c
> @@ -850,7 +850,8 @@ static long wmi_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> buf->length, wblock->req_buf_size);
>
> /* copy the structure from userspace */
> - if (copy_from_user(buf, input, wblock->req_buf_size)) {
> + if (copy_from_user(buf->data, input->data,
> + wblock->req_buf_size - sizeof(buf->length))) {
> dev_dbg(&wblock->dev.dev, "Copy %llu from user failed\n",
> wblock->req_buf_size);
> ret = -EFAULT;
> --
> 2.17.2 (Apple Git-113)
>


--
With Best Regards,
Andy Shevchenko

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