Re: [PATCH v2] sanitize task->comm to avoid leaking escape codes

[Kees Cook <kees.cook@canonical.com>]

On Tue, Jun 29, 2010 at 10:36:50AM +0100, Alan Cox wrote:
> > Through get_task_comm() and many direct uses of task->comm in the kernel,
> > it is possible for escape codes and other non-printables to leak into
> > dmesg, syslog, etc.  In the worst case, these strings could be used to
> > attack administrators using vulnerable terminal emulators, and at least
> > cause confusion through the injection of \r characters.
> 
> If an administrator has a vulnerable terminal emulator they have other
> problems.

Totally agreed.

> Please do any filtering you must in the yama security module where it
> only affects that. One way to approach it without losing data within the
> module might be to use HTML style encoding within Yama so your own tools
> can undo the 'sanitizing' rather than losing information ?

I'm not interested in sanitizing this in Yama.  The use of task->comm via
printk was seen as a flaw.  I didn't agree (see above about terminal),
and suggested that if it was a flaw, it was a flaw with printk or
task->comm itself.  Since "fixing" both of those have been vetoed,
I have no more interest in the filtering.

What I do have interest in is fixing get_task_comm's use of buffers, which
is theoretically problematic in some future where someone accidentally
calls it with a buffer smaller than sizeof(task->comm).

I'll send a patch that only fixes that and leaves out the filtering.

-Kees

-- 
Kees Cook
Ubuntu Security Team