linux-kernel - Re: [RFC v2] ptrace, pidfd: add pidfd

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Message-ID: <20200428074502.ruqlxqqgnoyqvhwv@wittgenstein>
Date:   Tue, 28 Apr 2020 09:45:02 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Hagen Paul Pfeifer <hagen@...u.net>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Aleksa Sarai <cyphar@...har.com>,
        Arnd Bergmann <arnd@...db.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Jann Horn <jannh@...gle.com>,
        kernel list <linux-kernel@...r.kernel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian@...uner.io>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Brian Gerst <brgerst@...il.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        David Howells <dhowells@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Linux API <linux-api@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [RFC v2] ptrace, pidfd: add pidfd_ptrace syscall

On Tue, Apr 28, 2020 at 08:39:35AM +0200, Hagen Paul Pfeifer wrote:
> * Linus Torvalds | 2020-04-27 21:28:14 [-0700]:
> 
> >> I hate to say this, but I’m not convinced that asking the gdb folks is
> >> the right approach. GDB has an ancient architecture and is
> >> *incredibly* buggy. I’m sure ptrace is somewhere on the pain point
> >> list, but I suspect it’s utterly dwarfed by everything else.
> >
> >You may be right. However, if gdbn isn't going to use it, then I
> >seriously don't think it's worth changing much.
> >
> >It might be worth looking at people who don't use ptrace() for
> >debugging, but for "incidental" reasons. IOW sandboxing, tracing,
> >things like that.
> >
> >Maybe those people want things that are simpler and don't actually
> >need the kinds of hard serialization that ptrace() wants.
> >
> >I'd rather add a few really simple things that might not be a full
> >complement of operations for a debugger, but exactly because they
> >aren't a full debugger, maybe they are things that we can tell are
> >obviously secure and simple?
> 
> Okay, to sum up the the whole discussion: we go forward with Jann's proposal
> by simple adding PTRACE_ATTACH_PIDFD and friends. This is the minimal invasive
> solution and the risk of an potenial security problem is almost not present[TM].
> 
> Changing the whole ptrace API is a different beast. I rather believe that I
> see Linus Linux successor rather than a ptrace successor.
> 
> I am fine with PTRACE_ATTACH_PIDFD!

If this is enough for you use-case then we should make due with my
initial suggestion, yes. I'd be fine with adding this variant.

I initially thought that we'd likely would need to support a few more
but I don't think we want to actually; there's a bunch of crazy stuff in
there.

Christian