Re: [PATCH 5/7] SELinux: Handle opening of a unioned file

[Stephen Smalley <sds@tycho.nsa.gov>]

On 06/12/2015 11:30 AM, David Howells wrote:
> Hi Stephen,
> 
> David Howells <dhowells@redhat.com> wrote:
> 
>> Stephen Smalley <sds@tycho.nsa.gov> wrote:
>>
>>> Also, would be good to create a common helper for use here, by
>>> selinux_dentry_init_security(), selinux_inode_init_security(), and
>>> may_create().  Already some seeming potential for inconsistencies there.
>>
>> selinux_dentry_init_security() and selinux_inode_init_security() do
>> something different depending on SECURITY_FS_USE_MNTPOINT.  Is the dentry
>> variant wrong?  Shouldn't it be using the mountpoint label if that flag _is_
>> set?
> 
> Any answer to that?

It looks like commit 415103f9932d45f7927f4b17e3a9a13834cdb9a1 changed
selinux_inode_init_security()'s handling of SECURITY_FS_USE_MNTPOINT,
and this change was never propagated to selinux_dentry_init_security().
 However, that commit also did not update
security/selinux/hooks.c:may_create()'s logic for computing the new file
label when checking CREATE permission, and therefore introduced a
potential inconsistency between the label used for the permission check
and the label assigned to the inode.

That's why I suggested that we need a common helper for all three to
ensure consistency there.