linux-kernel - Re: [PATCH 3/3] security: Yama: add ptrace relationship tracking interface

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Message-ID: <20111119165903.GB2208@openwall.com>
Date:	Sat, 19 Nov 2011 20:59:03 +0400
From:	Solar Designer <solar@...nwall.com>
To:	kernel-hardening@...ts.openwall.com
Cc:	Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH 3/3] security: Yama: add ptrace relationship tracking interface

On Sat, Nov 19, 2011 at 08:30:58PM +0400, Vasiliy Kulikov wrote:
> On Wed, Oct 26, 2011 at 16:49 -0700, Kees Cook wrote:
> > +	if (mode == PTRACE_MODE_ATTACH &&
> > +	    ptrace_scope &&
> > +	    !capable(CAP_SYS_PTRACE) &&
> > +	    !task_is_descendant(current, child) &&
> > +	    !ptracer_exception_found(current, child))
> > +		rc = -EPERM;
> 
> capable() is better to put after all other tests

Right, but...

> as a failed capable()
> might emit a false positive warning into logs or something.

...primarily for another reason: a successful capable() sets
PF_SUPERPRIV, whereas the permission might have been granted without
capable() as well.  The PF_SUPERPRIV flag is visible via BSD process
accounting.

Alexander
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