linux-kernel - Re: [PATCH v3 06/11] smack: don't use implicit star to display smackfs/syslog

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Date:	Thu, 30 Jul 2015 17:42:56 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Lukasz Pawelczyk <l.pawelczyk@...sung.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Arnd Bergmann <arnd@...db.de>,
	Casey Schaufler <casey@...aufler-ca.com>,
	David Howells <dhowells@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Eric Paris <eparis@...isplace.org>,
	Fabian Frederick <fabf@...net.be>,
	Greg KH <gregkh@...uxfoundation.org>,
	James Morris <james.l.morris@...cle.com>,
	Jiri Slaby <jslaby@...e.com>, Joe Perches <joe@...ches.com>,
	John Johansen <john.johansen@...onical.com>,
	Jonathan Corbet <corbet@....net>,
	Kees Cook <keescook@...omium.org>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	NeilBrown <neilb@...e.de>, Oleg Nesterov <oleg@...hat.com>,
	Paul Moore <paul@...l-moore.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Zefan Li <lizefan@...wei.com>, linux-doc@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
	havner@...il.com
Subject: Re: [PATCH v3 06/11] smack: don't use implicit star to display
 smackfs/syslog

On Fri, Jul 24, 2015 at 12:04:40PM +0200, Lukasz Pawelczyk wrote:
> Smackfs/syslog is analogous to onlycap and unconfined. When not filled
> they don't do anything. In such cases onlycap and unconfined displayed
> nothing when read, but syslog unconditionally displayed star. This
> doesn't work well with namespaces where the star could have been
> unmapped. Besides the meaning of this star was different then a star
> that could be written to this file. This was misleading.
> 
> This also brings syslog read/write functions on par with onlycap and
> unconfined where it is possible to reset the value to NULL as should be
> possible according to comment in smackfs.c describing smack_syslog_label
> variable.
> 
> Before that the initial state was to allow (smack_syslog_label was
> NULL), but after writing star to it the current had to be labeled star
> as well to have an access, even thought reading the smackfs/syslog
> returned the same result in both cases.
> 
> Signed-off-by: Lukasz Pawelczyk <l.pawelczyk@...sung.com>

Acked-by: Serge Hallyn <serge.hallyn@...onical.com>

> ---
>  security/smack/smackfs.c | 42 +++++++++++++++++++++++++++---------------
>  1 file changed, 27 insertions(+), 15 deletions(-)
> 
> diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
> index 81a2888..89f847bba 100644
> --- a/security/smack/smackfs.c
> +++ b/security/smack/smackfs.c
> @@ -2362,23 +2362,20 @@ static const struct file_operations smk_change_rule_ops = {
>  static ssize_t smk_read_syslog(struct file *filp, char __user *buf,
>  				size_t cn, loff_t *ppos)
>  {
> -	struct smack_known *skp;
> +	char *smack = "";
>  	ssize_t rc = -EINVAL;
>  	int asize;
>  
>  	if (*ppos != 0)
>  		return 0;
>  
> -	if (smack_syslog_label == NULL)
> -		skp = &smack_known_star;
> -	else
> -		skp = smack_syslog_label;
> +	if (smack_syslog_label != NULL)
> +		smack = smack_syslog_label->smk_known;
>  
> -	asize = strlen(skp->smk_known) + 1;
> +	asize = strlen(smack) + 1;
>  
>  	if (cn >= asize)
> -		rc = simple_read_from_buffer(buf, cn, ppos, skp->smk_known,
> -						asize);
> +		rc = simple_read_from_buffer(buf, cn, ppos, smack, asize);
>  
>  	return rc;
>  }
> @@ -2406,16 +2403,31 @@ static ssize_t smk_write_syslog(struct file *file, const char __user *buf,
>  	if (data == NULL)
>  		return -ENOMEM;
>  
> -	if (copy_from_user(data, buf, count) != 0)
> +	if (copy_from_user(data, buf, count) != 0) {
>  		rc = -EFAULT;
> -	else {
> -		skp = smk_import_entry(data, count);
> -		if (IS_ERR(skp))
> -			rc = PTR_ERR(skp);
> -		else
> -			smack_syslog_label = skp;
> +		goto freeout;
>  	}
>  
> +	/*
> +	 * Clear the smack_syslog_label on invalid label errors. This means
> +	 * that we can pass a null string to unset the syslog value.
> +	 *
> +	 * Importing will also reject a label beginning with '-',
> +	 * so "-syslog" will also work.
> +	 *
> +	 * But do so only on invalid label, not on system errors.
> +	 */
> +	skp = smk_import_entry(data, count);
> +	if (PTR_ERR(skp) == -EINVAL)
> +		skp = NULL;
> +	else if (IS_ERR(skp)) {
> +		rc = PTR_ERR(skp);
> +		goto freeout;
> +	}
> +
> +	smack_syslog_label = skp;
> +
> +freeout:
>  	kfree(data);
>  	return rc;
>  }
> -- 
> 2.4.3
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