linux-kernel - Re: [PATCH 4/4] module: Add hook for security_kernel_post_read

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Date:   Tue, 07 Jul 2020 20:47:20 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Kees Cook <keescook@...omium.org>, James Morris <jmorris@...ei.org>
Cc:     Jessica Yu <jeyu@...nel.org>, Luis Chamberlain <mcgrof@...nel.org>,
        Scott Branden <scott.branden@...adcom.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Matthew Garrett <matthewgarrett@...gle.com>,
        David Howells <dhowells@...hat.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        KP Singh <kpsingh@...gle.com>, Dave Olsthoorn <dave@...aar.me>,
        Hans de Goede <hdegoede@...hat.com>,
        Peter Jones <pjones@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Boyd <stephen.boyd@...aro.org>,
        Paul Moore <paul@...l-moore.com>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH 4/4] module: Add hook for
 security_kernel_post_read_file()

On Tue, 2020-07-07 at 01:19 -0700, Kees Cook wrote:
> Calls to security_kernel_load_data() should be paired with a call to
> security_kernel_post_read_file() with a NULL file argument. Add the
> missing call so the module contents are visible to the LSMs interested
> in measuring the module content. (This also paves the way for moving
> module signature checking out of the module core and into an LSM.)
> 
> Cc: Jessica Yu <jeyu@...nel.org>
> Fixes: c77b8cdf745d ("module: replace the existing LSM hook in init_module")
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  kernel/module.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index 0c6573b98c36..af9679f8e5c6 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2980,7 +2980,12 @@ static int copy_module_from_user(const void __user *umod, unsigned long len,
>  		return -EFAULT;
>  	}
>  
> -	return 0;
> +	err = security_kernel_post_read_file(NULL, (char *)info->hdr,
> +					     info->len, READING_MODULE);

There was a lot of push back on calling security_kernel_read_file()
with a NULL file descriptor here.[1]  The result was defining a new
security hook - security_kernel_load_data - and enumeration -
LOADING_MODULE.  I would prefer calling the same pre and post security
hook.

Mimi

[1] http://kernsec.org/pipermail/linux-security-module-archive/2018-Ma
y/007110.html

> +	if (err)
> +		vfree(info->hdr);
> +
> +	return err;
>  }
>  
>  static void free_copy(struct load_info *info)