From: Jann Horn <jann@thejh.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Roland McGrath <roland@hack.frob.com>,
Oleg Nesterov <oleg@redhat.com>,
John Johansen <john.johansen@canonical.com>,
James Morris <james.l.morris@oracle.com>,
"Serge E. Hallyn" <serge@hallyn.com>,
Paul Moore <aul@paul-moore.com>,
Stephen Smalley <sds@tycho.nsa.gov>,
Eric Paris <eparis@parisplace.org>,
Casey Schaufler <casey@schaufler-ca.com>,
Kees Cook <eescook@chromium.org>,
Andrew Morton <akpm@linux-foundation.org>,
Janis Danisevskis <jdanis@google.com>,
Seth Forshee <seth.forshee@canonical.com>,
"Eric . Biederman" <ebiederm@xmission.com>,
Thomas Gleixner <tglx@linutronix.de>,
Benjamin LaHaise <bcrl@kvack.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
LSM List <linux-security-module@vger.kernel.org>,
"security@kernel.org" <security@kernel.org>
Subject: Re: [PATCH 7/9] ptrace: forbid ptrace checks against current_cred() from VFS context
Date: Sun, 18 Sep 2016 22:52:39 +0200 [thread overview]
Message-ID: <20160918205239.GB2903@pc.thejh.net> (raw)
In-Reply-To: <CA+55aFwWSWJc17cpNUqWUUahp81zomSpOamDmF_JhYTRZoLecA@mail.gmail.com>
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On Sun, Sep 18, 2016 at 01:18:48PM -0700, Linus Torvalds wrote:
> On Sun, Sep 18, 2016 at 8:05 AM, Jann Horn <jann@thejh.net> wrote:
> > This ensures that VFS implementations don't call ptrace_may_access() from
> > VFS read or write handlers. In order for file descriptor passing to have
> > its intended security properties, VFS read/write handlers must not do any
> > kind of privilege checking.
>
> Quite frankly, this smells like it should be a static check, not some
> kind of runtime one. Or if runtime, it should be abstracted out so
> that you can do an occasional "let's run a checking pass" rather than
> enable it unconditionally and universally.
Hm, fair point.
I guess this could be implemented in eBPF or systemtap?
Then for now, I guess I'll remove this patch from the series - and maybe
I'll think about writing some external checker with eBPF kprobes or so.
> It's just too specialized. Soon you'll want to do other random context
> checking, and we can't just keep adding those kinds of ad-hoc things
> without it becoming a maintenance nightmare. I can well imagine
> somebody ending up writing some stupid patch to take that
> "in_unprivileged_vfs" thing into account for some semantics, and then
> we're *really* screwed. So there are many reasons to make sure this is
> *not* something that people actually expect to always be there.
Oh, yuck. Yes, those are good points.
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next prev parent reply other threads:[~2016-09-18 20:52 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-18 15:05 [PATCH 0/9] Various fixes related to ptrace_may_access() Jann Horn
2016-09-18 15:05 ` [PATCH 1/9] exec: introduce cred_guard_light Jann Horn
2016-09-18 15:05 ` [PATCH 2/9] exec: turn self_exec_id into self_privunit_id Jann Horn
2016-09-18 18:13 ` Ben Hutchings
2016-09-18 18:31 ` Jann Horn
2016-09-18 18:45 ` Ben Hutchings
2016-09-18 19:08 ` Jann Horn
2016-09-18 19:57 ` Andy Lutomirski
2016-09-19 15:31 ` Jann Horn
2016-09-18 15:05 ` [PATCH 3/9] proc: use open()-time creds for ptrace checks Jann Horn
2016-09-19 13:01 ` Stephen Smalley
2016-09-19 14:32 ` Jann Horn
2016-09-19 14:45 ` Stephen Smalley
2016-09-18 15:05 ` [PATCH 4/9] futex: don't leak robust_list pointer Jann Horn
2016-09-18 18:28 ` Ben Hutchings
2016-09-18 18:33 ` Jann Horn
2016-09-18 15:05 ` [PATCH 5/9] proc: lock properly in ptrace_may_access callers Jann Horn
2016-09-18 19:15 ` Jann Horn
2016-09-18 15:05 ` [PATCH 6/9] ptrace: warn on ptrace_may_access without proper locking Jann Horn
2016-09-18 15:05 ` [PATCH 7/9] ptrace: forbid ptrace checks against current_cred() from VFS context Jann Horn
2016-09-18 18:38 ` Ben Hutchings
2016-09-18 18:40 ` Jann Horn
2016-09-18 19:57 ` Andy Lutomirski
2016-09-18 20:38 ` Jann Horn
2016-09-18 20:18 ` Linus Torvalds
2016-09-18 20:52 ` Jann Horn [this message]
2016-09-18 15:05 ` [PATCH 8/9] fs/proc: fix attr access check Jann Horn
2016-09-18 15:05 ` [PATCH 9/9] Documentation: add security/ptrace_checks.txt Jann Horn
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