Re: [Bug #11500] /proc/net bug related to selinux

Stephen Smalley
2008-09-15T13:42:14Z

On Mon, 2008-09-15 at 09:05 -0400, Stephen Smalley wrote:
> On Sat, 2008-09-13 at 12:37 -0700, Andrew Morton wrote:
> > On Sat, 13 Sep 2008 10:15:43 +1000 (EST) James Morris <jmorris-gx6/JNMH7DfYtjvyW6yDsg@public.gmane.org> wrote:
> >
> > > On Fri, 12 Sep 2008, Andrew Morton wrote:
> > >
> > > > > > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=11500
> > > > > > Subject : /proc/net bug related to selinux
> > > > > > Submitter : Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
> > > > > > Date : 2008-09-04 17:45 (9 days old)
> > > > > > References : http://marc.info/?l=linux-kernel&m=122055041313270&w=4
> > > > >
> > > > > I think this might be a regression caused by namespace changes which we
> > >
> > > By which I mean, this was caused by a non-SELinux change to the upstream
> > > kernel many, many eons ago.
> >
> > hm, seems that 2.6.24 is OK but 2.6.25 is not. I must have missed the
> > bug when testing 2.6.25-based kernels.
> >
> > I started a git bisection search but after half an hour I hit bad
> > bisection breakage: a complete machine hang in fib_rules_init().
> >
> > > > > addressed in SELinux policy. Which distro version & policy version is
> > > > > this seen with?
> > > > >
> > > >
> > > > FC5 on x86_32 and FC6 on x86_64.
> > >
> > > As mentioned in the bugzilla, any related avc messages would be useful.
> >
> > 2.6.25 dmesg: http://userweb.kernel.org/~akpm/dmesg-sony.txt
> > /var/log/messages: http://userweb.kernel.org/~akpm/messages-sony.txt
> >
> > The latter includes this:
> >
> > Sep 13 12:32:43 sony kernel: SELinux: class key not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: class dccp_socket not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: class memprotect not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: class peer not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: class capability2 not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: permission open in class dir not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: permission open in class file not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: permission open in class chr_file not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: permission open in class blk_file not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: permission open in class fifo_file not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: permission dccp_recv in class node not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: permission dccp_send in class node not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: permission recvfrom in class node not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: permission sendto in class node not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: permission dccp_recv in class netif not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: permission dccp_send in class netif not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: permission ingress in class netif not defined in policy
> > Sep 13 12:32:43 sony kernel: SELinux: permission egress in class netif not defined in policy
> > Sep 13 12:32:44 sony kernel: SELinux: permission setkeycreate in class process not defined in policy
> > Sep 13 12:32:44 sony kernel: SELinux: permission setsockcreate in class process not defined in policy
> > Sep 13 12:32:44 sony kernel: SELinux: permission setfcap in class capability not defined in policy
> > Sep 13 12:32:44 sony kernel: SELinux: permission polmatch in class association not defined in policy
> > Sep 13 12:32:44 sony kernel: SELinux: permission flow_in in class packet not defined in policy
> > Sep 13 12:32:44 sony kernel: SELinux: permission flow_out in class packet not defined in policy
> > Sep 13 12:32:44 sony kernel: SELinux: permission forward_in in class packet not defined in policy
> > Sep 13 12:32:44 sony kernel: SELinux: permission forward_out in class packet not defined in policy
> > Sep 13 12:32:44 sony kernel: SELinux: the above unknown classes and permissions will be denied
> > Sep 13 12:32:44 sony kernel: type=1403 audit(1221309118.644:3): policy loaded auid=4294967295 ses=4294967295
> > Sep 13 12:32:44 sony kernel: type=1400 audit(1221334321.726:4): avc: denied { audit_write } for pid=400 comm="hwclock" capability=29 scontext=system_u:system_r:hwclock_t:s0 tcontext=system_u:system_r:hwclock_t:s0 tclass=capability
> >
> >
> > Why am I seeing this on two machines and two vanilla-installed distros
> > but nobody else is reporting it?
>
> What we actually need to see is the output of:
> /sbin/ausearch -i -m AVC -sv no
>
> However, the most likely explanation is simply that when /proc/net was
> changed from being a directory to being a symlink to /proc/self/net,
> that introduced an additional permission check on accesses
> of /proc/net/<whatever>, namely the read check on the symlink itself.
> And since that check wasn't happening on /proc/net accesses with older
> kernels, older policies didn't allow it.
>
> As to why others haven't reported it, I expect that they have updated
> their policies to newer ones that allow the necessary access. The fact
> that legacy distros wouldn't have such updated policies isn't surprising
> - they don't push updates to those distros for new kernels. FC5 and FC6
> are both EOL'd, right?
>
> In any event, we didn't change anything in SELinux - the change was
> elsewhere (in the proc/net implementation). Don't blame the messenger
> please.

BTW, if the explanation above is correct, then a user can allow this
permission in their own policy by creating a local policy module and
inserting it, ala:
$ cat fixprocnet.te
policy_module(fixprocnet, 1.0)
require {
attribute domain;
type proc_net_t;
}
# Allow all domains to read the /proc/net symlink.
allow domain proc_net_t:lnk_file read;

$ make -f /usr/share/selinux/devel/Makefile fixprocnet.pp
$ /usr/sbin/semodule -i fixprocnet.pp

Requires selinux-policy-devel to be installed.

--
Stephen Smalley
National Security Agency