linux-kernel - Re: [PATCH v3 2/2] ima: check signature enforcement against cmdline param instead of CONFIG

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Message-Id: <1508885697.3164.5.camel@linux.vnet.ibm.com>
Date:   Tue, 24 Oct 2017 18:54:57 -0400
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     "Bruno E. O. Meneguele" <brdeoliv@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, serge@...lyn.com,
        james.l.morris@...cle.com, dmitry.kasatkin@...il.com,
        rusty@...tcorp.com.au, jeyu@...nel.org
Subject: Re: [PATCH v3 2/2] ima: check signature enforcement against cmdline
 param instead of CONFIG

On Tue, 2017-10-24 at 15:37 -0200, Bruno E. O. Meneguele wrote:
> When the user requests MODULE_CHECK policy and its kernel is compiled
> with CONFIG_MODULE_SIG_FORCE not set, all modules would not load, just
> those loaded in initram time. One option the user would have would be
> set a kernel cmdline param (module.sig_enforce) to true, but the IMA
> module check code doesn't rely on this value, it checks just
> CONFIG_MODULE_SIG_FORCE.
> 
> This patch solves this problem checking for the exported value of
> module.sig_enforce cmdline param intead of CONFIG_MODULE_SIG_FORCE,
> which holds the effective value (CONFIG || param).
> 
> Signed-off-by: Bruno E. O. Meneguele <brdeoliv@...hat.com>
> ---
>  security/integrity/ima/ima_main.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index e4ab8ef8016e..d11a7fcc5c8b 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -356,12 +356,12 @@ void ima_post_path_mknod(struct dentry *dentry)
>   */
>  int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
>  {
> +	bool sig_enforce = is_module_sig_enforced();
> +
>  	if (!file && read_id == READING_MODULE) {

The only reason for getting here is that you're using the old module
load syscall.  Is there a reason for not using the new one, which
passes the file descriptor?

thanks,

Mimi

> -#ifndef CONFIG_MODULE_SIG_FORCE
> -		if ((ima_appraise & IMA_APPRAISE_MODULES) &&
> +		if (!sig_enforce && (ima_appraise & IMA_APPRAISE_MODULES) &&
>  		    (ima_appraise & IMA_APPRAISE_ENFORCE))
>  			return -EACCES;	/* INTEGRITY_UNKNOWN */
> -#endif
>  		return 0;	/* We rely on module signature checking */
>  	}
>  	return 0;