Re: [PATCH 2/2] RFC: selinux: sysctl: fix selinux labeling brokenby last patch

From: Stephen Smalley
Date: Mon Jan 31 2011 - 08:59:46 EST

On Mon, 2011-01-31 at 05:26 +0200, Lucian Adrian Grijincu wrote:
> Eric's patch was rejected because it broke selinux labeling:
> This seems to break labeling. Prior to this patch, I see:
> # ls -lZ /proc/1/net/rpc/nfsd.fh
> -rw-------. root root system_u:object_r:sysctl_rpc_t:s0 channel
> with the patch:
> # ls -lZ /proc/1/net/rpc/nfsd.fh
> -rw-------. root root system_u:object_r:proc_t:s0 channel
> My patch seems to have fixed this problem (it correctly reports
> sysctl_rpc_t in this case), but my selinux experience is Î > 0 and I
> have no ideea what else it may have broken.
> I ran 'find /proc | xargs ls -Z > f' on a kernel with an without
> these patches:
> *
> *
> My setup is a custom busybox live CD with selinux enabled, with
> /etc/selinux and /usr/share/selinux/default copied from Ubuntu 10.10's
> selinux-policy-default package. I'm sure there are lots of reasons why
> this is not correcly configured, etc., but I have no experience
> regarding selinux. I can make all the scripts/sources/configs/etc
> available to anyone interested.
> NOTE: this patch will be merged with:
> security/selinux: Simplify proc inode to security label mapping
> I'm only prividing this patch separately to point out the differences
> to Eric W. Biederman's patch.
> Both of these patches apply cleanly agains Linux 2.6.37.
> Signed-off-by: Lucian Adrian Grijincu <lucian.grijincu@xxxxxxxxx>
> ---
> fs/proc/proc_sysctl.c | 1 -
> security/selinux/hooks.c | 20 ++++++++++++++++----
> 2 files changed, 16 insertions(+), 5 deletions(-)

It would be better to include the patch inline for review. In any
event, a few observations on your patch:
- We don't want to replace "incestuous" knowledge of proc with
"incestous" knowledge of the dcache. So rather than encoding knowledge
of the magical "//deleted" suffix into selinux, use an interface to the
dcache (or add one if none exists) that does not append that suffix at
all. I think apparmor did something similar to deal with the (deleted)
suffix for d_path.

- You don't need special handling of /proc/PID entries. Those are
labeled via the security_task_to_inode -> selinux_task_to_inode hook,
called from proc_pid_make_inode and the _revalidate functions.

- Don't remove the IS_PRIVATE() test from inode_has_perm(), as other
inodes beyond just the /proc/sys ones are marked with that flag
(original usage was for reiserfs xattr inodes).

Stephen Smalley
National Security Agency

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