linux-kernel - Re: [PATCH v2 2/3] mm: add LSM hook for writes to readonly memory

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Message-ID: <20160929062510.GB21794@gmail.com>
Date:   Thu, 29 Sep 2016 08:25:10 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Jann Horn <jann@...jh.net>
Cc:     security@...nel.org, Alexander Viro <viro@...iv.linux.org.uk>,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Eric Paris <eparis@...isplace.org>,
        James Morris <james.l.morris@...cle.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Nick Kralevich <nnk@...gle.com>,
        Janis Danisevskis <jdanis@...gle.com>,
        linux-security-module@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] mm: add LSM hook for writes to readonly memory


* Jann Horn <jann@...jh.net> wrote:

> +/*
> + * subject_cred must be the subjective credentials using which access is
> + * requested.
> + * object_cred must be the objective credentials of the target task at the time
> + * the mm_struct was acquired.
> + * Both of these may be NULL if FOLL_FORCE is unset or FOLL_WRITE is unset.

Hm, I have trouble parsing the first sentence.

> -	return __get_user_pages_locked(current, current->mm, start, nr_pages,
> -				       write, force, pages, vmas, NULL, false,
> -				       FOLL_TOUCH);
> +	return __get_user_pages_locked(current, current->mm, current_cred(),
> +				       current_real_cred(), start,
> +				       nr_pages, write, force, pages, vmas,
> +				       NULL, false, FOLL_TOUCH);

So the parameter passing was disgustig before, and now it became super disgusing! 

Would it improve the code if we added a friendly helper structure (or two if 
that's better) to clean up all the interactions within these various functions?

Thanks,

	Ingo