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

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Message-ID: <87fsnf2ucx.fsf@email.froward.int.ebiederm.org>
Date:   Fri, 18 Mar 2022 09:44:30 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Kees Cook <keescook@...omium.org>
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

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?

Eric