linux-kernel - Re: [PATCH 7/8] SELinux: Create a common helper to determine an inode label

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Date:	Thu, 18 Jun 2015 16:32:36 +0100
From:	David Howells <dhowells@...hat.com>
To:	Stephen Smalley <sds@...ho.nsa.gov>
Cc:	dhowells@...hat.com, viro@...iv.linux.org.uk, miklos@...redi.hu,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-unionfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	SELinux <selinux@...ho.nsa.gov>, Paul Moore <paul@...l-moore.com>
Subject: Re: [PATCH 7/8] SELinux: Create a common helper to determine an inode label

Stephen Smalley <sds@...ho.nsa.gov> wrote:

> > Fair point.  What does SBLABEL_MNT mean precisely?  It seems to indicate one
> > of an odd mix of behaviours.  I presume it means that we *have* to calculate a
> > label and can't get one from the underlying fs if it is not set.
> 
> It means the filesystem supports per-file labeling and you can use
> setxattr(..."security.selinux") and setfscreatecon() for files on it.
> You can see whether it is set on a filesystem by looking for the
> seclabel option in cat /proc/mounts.  If it is not set, then we ignore
> tsec->create_sid.  It is arguable as to whether it is correct to always
> call security_transition_sid() there either, but that's another topic.

Okay, so how about the attached?

David
---
static int selinux_determine_inode_label(const struct inode *dir,
					 const struct qstr *name,
					 const char *caller,
					 u16 tclass,
					 u32 *_new_isid)
{
	const struct superblock_security_struct *sbsec = dir->i_sb->s_security;
	const struct inode_security_struct *dsec = dir->i_security;
	const struct task_security_struct *tsec = current_security();

	if ((sbsec->flags & SE_SBINITIALIZED) &&
	    (sbsec->behavior == SECURITY_FS_USE_MNTPOINT)) {
		*_new_isid = sbsec->mntpoint_sid;
	} else if ((sbsec->flags & SBLABEL_MNT) &&
		   tsec->create_sid) {
		*_new_isid = tsec->create_sid;
	} else {
		return security_transition_sid(tsec->sid, dsec->sid, tclass,
					       name, _new_isid);
	}

	return 0;
}
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