linux-kernel - Re: [PATCH 1/2] ptrace: Move setting/clearing ptrace_message into ptrace

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Date:   Fri, 18 Mar 2022 10:20:46 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexey Gladkov <legion@...nel.org>,
        Kyle Huey <me@...ehuey.com>, Oleg Nesterov <oleg@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>, linux-api@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 1/2] ptrace: Move setting/clearing ptrace_message into
 ptrace_stop

On Fri, Mar 18, 2022 at 09:44:30AM -0500, Eric W. Biederman wrote:
> Kees Cook <keescook@...omium.org> writes:
> 
> > On Tue, Mar 15, 2022 at 06:21:08PM -0500, Eric W. Biederman wrote:
> >> 
> >> Today ptrace_message is easy to overlook as it not a core part of
> >> ptrace_stop.  It has been overlooked so much that there are places
> >> that set ptrace_message and don't clear it, and places that never set
> >> it.  So if you get an unlucky sequence of events the ptracer may be
> >> able to read a ptrace_message that does not apply to the current
> >> ptrace stop.
> >> 
> >> Move setting of ptrace_message into ptrace_stop so that it always gets
> >> set before the stop, and always gets cleared after the stop.  This
> >> prevents non-sense from being reported to userspace and makes
> >> ptrace_message more visible in the ptrace helper functions so that
> >> kernel developers can see it.
> >> 
> >> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> >
> > This looks good to me. Did you happen to run the seccomp selftests
> > before/after these changes?
> 
> I did not.  This is a pure ptrace change.  Do you see a way that seccomp
> could be involved?

Sorry, that wasn't clear: seccomp includes a number of ptrace tests as
well, especially involving handling process death, messages, and
signals. I'll give it a spin; so far it seems fine.

-- 
Kees Cook