Re: [PATCH] dm ioctl: prevent stack leak in dm ioctl call

[Alasdair G Kergon <agk@redhat.com>]

On Tue, Apr 25, 2017 at 05:57:41PM -0700, Adrian Salido wrote:
> 1. param_kernel is allocated from stack and passed to copy_params
> 2. copy_params only copies up to param_kernel->data from user
> (param_kernel->data still contains stack contents)
> 3. in copy_params, since there are no params it will skip through and
> return param = dmi = param_kernel

after setting
  dmi->data_size = minimum_data_size;

and then         
  input_param_size = param->data_size;

> 4. that stale data is copied back to user
because it is incorrectly extending the buffer?
  param->data_size = sizeof(*param);
instead of continuing to use input_param_size?

Alasdair