linux-kernel - Re: [PATCH] LSM: Allow syzbot to ignore security= parameter.

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Date:   Fri, 8 Feb 2019 08:23:33 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Kees Cook <keescook@...omium.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        syzbot <syzbot+21016130b0580a9de3b5@...kaller.appspotmail.com>,
        tyhicks@...onical.com, John Johansen <john.johansen@...onical.com>,
        James Morris <jmorris@...ei.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-security-module@...r.kernel.org,
        Serge Hallyn <serge@...lyn.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Jeffrey Vander Stoep <jeffv@...gle.com>,
        SELinux <selinux@...r.kernel.org>,
        Russell Coker <russell@...er.com.au>,
        Laurent Bigonville <bigon@...ian.org>,
        syzkaller <syzkaller@...glegroups.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] LSM: Allow syzbot to ignore security= parameter.

On 2/8/2019 2:52 AM, Tetsuo Handa wrote:
> On 2019/02/08 1:24, Casey Schaufler wrote:
>>>>> Then, I think that it is straightforward (and easier to manage) to ignore security= parameter
>>>>> when lsm= parameter is specified.
>>>> That reduces flexibility somewhat. If I am debugging security modules
>>>> I may want to use lsm= to specify the order while using security= to
>>>> identify a specific exclusive module. I could do that using lsm= by
>>>> itself, but habits die hard.
>>> "lsm=" can be used for identifying a specific exclusive module, and Ubuntu kernels would
>>> have to use CONFIG_LSM (or "lsm=") for identifying the default exclusive module (in order
>>> to allow enabling both TOMOYO and one of SELinux,Smack,AppArmor at the same time).
>>>
>>> Since "security=" can't be used for selectively enable/disable more than one of
>>> SELinux,Smack,TOMOYO,AppArmor, I think that recommending users to migrate to "lsm=" is the
>>> better direction. And ignoring "security=" when "lsm=" is specified is easier to understand.
>> I added Kees to the CC list. Kees, what to you think about
>> ignoring security= if lsm= is specified? I'm ambivalent.
>>
>>
> To help administrators easily understand what LSM modules are possibly enabled by default (which
> have to be fetched from e.g. /boot/config-`uname -r`)

$ cat /sys/kernel/security/lsm

>  and specify lsm= parameter when they need,
> I propose changes shown below.
>
> diff --git a/security/security.c b/security/security.c
> index 3147785e..051d708 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -51,8 +51,6 @@
>  static __initdata const char *chosen_lsm_order;
>  static __initdata const char *chosen_major_lsm;
>  
> -static __initconst const char * const builtin_lsm_order = CONFIG_LSM;
> -
>  /* Ordered list of LSMs to initialize. */
>  static __initdata struct lsm_info **ordered_lsms;
>  static __initdata struct lsm_info *exclusive;
> @@ -284,14 +282,22 @@ static void __init ordered_lsm_parse(const char *order, const char *origin)
>  static void __init ordered_lsm_init(void)
>  {
>  	struct lsm_info **lsm;
> +	const char *order = CONFIG_LSM;
> +	const char *origin = "builtin";
>  
>  	ordered_lsms = kcalloc(LSM_COUNT + 1, sizeof(*ordered_lsms),
>  				GFP_KERNEL);
>  
> -	if (chosen_lsm_order)
> -		ordered_lsm_parse(chosen_lsm_order, "cmdline");
> -	else
> -		ordered_lsm_parse(builtin_lsm_order, "builtin");
> +	if (chosen_lsm_order) {
> +		if (chosen_major_lsm) {
> +			pr_info("security= is ignored because of lsm=\n");
> +			chosen_major_lsm = NULL;
> +		}
> +		order = chosen_lsm_order;
> +		origin = "cmdline";
> +	}
> +	pr_info("Security Framework initializing: %s\n", order);
> +	ordered_lsm_parse(order, origin);
>  
>  	for (lsm = ordered_lsms; *lsm; lsm++)
>  		prepare_lsm(*lsm);
> @@ -333,8 +339,6 @@ int __init security_init(void)
>  	int i;
>  	struct hlist_head *list = (struct hlist_head *) &security_hook_heads;
>  
> -	pr_info("Security Framework initializing\n");
> -
>  	for (i = 0; i < sizeof(security_hook_heads) / sizeof(struct hlist_head);
>  	     i++)
>  		INIT_HLIST_HEAD(&list[i]);

I'm not going to object to this, but I don't see it as important.