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Re: [PATCH] libselinux init functions



On Mon, 2012-03-12 at 10:11 -0400, Stephen Smalley wrote:
> On Mon, 2012-03-12 at 18:17 +0800, Xin Ouyang wrote:
> > Hi all,
> > 
> > I am working on the newest release of SELinux userspace packages and
> > sysvinit, and find there are a defect for init function of libselinux.
> >   * libselinux-2.1.9
> >   * sysvinit-2.88dsf
> > 
> > AFAIK, while sysvinit is configured with SELinux, /sbin/init would be
> > linked to libselinux. So before /sbin/init running, init_selinuxmnt()
> > would be called.
> > 
> > // libselinux-2.1.9/src/init.c
> > 
> > static void init_lib(void) __attribute__ ((constructor));
> > static void init_lib(void)
> > {
> >         selinux_page_size = sysconf(_SC_PAGE_SIZE);
> >         init_selinuxmnt();
> > }
> > 
> > As called before /sbin/init, init_selinuxmnt() is called before any
> > other userspace process.
> > At this time, procfs(/proc) and selinuxfs(/sys/fs/selinux or /selinux)
> > have not been mounted, because kernel do not mount them.
> > 
> > So, after init_lib() -> init_selinuxmnt(), global variable
> > "selinux_mnt" is still null.
> > 
> > /sbin/init would call is_selinux_enabled() to check whether selinux
> > enabled. Because "selinux_mnt" is null, is_selinux_enabled() always
> > return 0.
> 
> /sbin/init isn't supposed to call is_selinux_enabled() before calling
> selinux_init_load_policy(), as is_selinux_enabled() will always return 0
> if policy has not yet been loaded.  That has always been true.  Sounds
> like you have an incorrect selinux patch for your sysvinit.
> 
> selinux_init_load_policy() internally tests whether SELinux is enabled
> in the kernel (by trying to mount selinuxfs) and will correctly return
> -1 with *enforce set to 0 so that the caller knows to proceed despite
> the failure to load.
> 
> Certainly the Debian sysvinit did it correctly in the past, as did the
> Fedora sysvinit (back when Fedora used sysvinit).

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=580272

-- 
Stephen Smalley
National Security Agency


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