linux-kernel - Re: [PATCH v2] exec: Set file unwritable before LSM check

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Message-ID: <alpine.LRH.2.21.1803191551580.5791@namei.org>
Date:   Mon, 19 Mar 2018 15:52:18 +1100 (AEDT)
From:   James Morris <jmorris@...ei.org>
To:     Kees Cook <keescook@...omium.org>
cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>
Subject: Re: [PATCH v2] exec: Set file unwritable before LSM check

On Fri, 9 Mar 2018, Kees Cook wrote:

> The LSM check should happen after the file has been confirmed to be
> unchanging. Without this, we could have a race between the Time of Check
> (the call to security_kernel_read_file() which could read the file and
> make access policy decisions) and the Time of Use (starting with
> kernel_read_file()'s reading of the file contents). In theory, file
> contents could change between the two.
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> v2: Clarify the ToC/ToU race (Linus)

Applied to
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git next-general
and next-testing


-- 
James Morris
<jmorris@...ei.org>