Re: [REVIEW][PATCH 1/3] ptrace: Capture the ptracer's creds not PT_PTRACE_CAP

[Kees Cook <keescook@chromium.org>]

On Thu, Nov 17, 2016 at 9:05 AM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
>
> When the flag PT_PTRACE_CAP was added the PTRACE_TRACEME path was
> overlooked.  This can result in incorrect behavior when an application
> like strace traces an exec of a setuid executable.
>
> Further PT_PTRACE_CAP does not have enough information for making good
> security decisions as it does not report which user namespace the
> capability is in.  This has already allowed one mistake through
> insufficient granulariy.
>
> I found this issue when I was testing another corner case of exec and
> discovered that I could not get strace to set PT_PTRACE_CAP even when
> running strace as root with a full set of caps.
>
> This change fixes the above issue with strace allowing stracing as
> root a setuid executable without disabling setuid.  More fundamentaly
> this change allows what is allowable at all times, by using the correct
> information in it's decision.
>
> Cc: stable@vger.kernel.org
> Fixes: 4214e42f96d4 ("v2.4.9.11 -> v2.4.9.12")
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
> [...]
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 348f51b0ec92..8fe58255d219 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1656,6 +1656,7 @@ struct task_struct {
>         struct list_head cpu_timers[3];
>
>  /* process credentials */
> +       const struct cred __rcu *ptracer_cred; /* Tracer's dredentials at attach */

Typo: credentials.

-Kees

-- 
Kees Cook
Nexus Security