Re: [PATCH] sanitize task->comm to avoid leaking escape codes

Kees Cook
2010-06-29T15:10:42Z

On Tue, Jun 29, 2010 at 11:45:14AM +0300, Alexey Dobriyan wrote:
> On Tue, Jun 29, 2010 at 12:03 AM, Kees Cook <kees.cook@canonical.com> wrote:
> > On Mon, Jun 28, 2010 at 01:00:28PM -0700, Andrew Morton wrote:
> >> Surely it would be better to fix the tools which display this info
> >> rather than making the kernel tell fibs.
> >
> > The strncpy in get_task_comm() is totally wrong -- it's testing the length
> > of task->comm.
>
> It also fills not just any buffer but buffer which is TASK_COMM_LEN byte wide.
>
> > Why should get_task_comm not take a destination buffer length argument?
>
> If you pass too small, you needlessly truncate output.

If you pass too small a buffer, get_task_comm will happily write all over
the caller's stack past the end of the buffer if the contents of task->comm
are large enough:

strncpy(buf, tsk->comm, sizeof(tsk->comm));

The "n" argument to get_task_comm's use of strncpy is totally wrong --
it needs to be the size of the destination, not the size of the source.
Luckily, everyone using get_task_comm currently uses buffers that are
sizeof(task->comm).

> If you pass too large, you waste space.

Right.

-Kees

--
Kees Cook
Ubuntu Security Team