Re: Mislabeled /proc/<pid>/ns/mnt files?

[Dominick Grift <dac.override@gmail.com>]

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On Fri, May 10, 2019 at 10:28:50AM -0400, Stephen Smalley wrote:
> On 5/10/19 3:12 AM, Dominick Grift wrote:
> > On Thu, May 09, 2019 at 02:47:30PM -0700, Jeffrey Vander Stoep wrote:
> > > From: Stephen Smalley <sds@tycho.nsa.gov>
> > > Date: Thu, May 9, 2019 at 2:17 PM
> > > To: Jeffrey Vander Stoep, <selinux@vger.kernel.org>, Joel Galenson,
> > > Petr Lautrbach
> > > 
> > > > On 5/9/19 3:56 PM, Jeffrey Vander Stoep wrote:
> > > > > I expected files here would have the process's context, but they
> > > > > don't. The files are actually all symlinks so it's entirely possible
> > > > > that the they shouldn't have the process's context. If that's the
> > > > > case, how can I provide different labels for them? Neither "proc" nor
> > > > > "unlabeled" are appropriate.
> > > > > 
> > > > > On a device with a 3.18 kernel they have the "proc" context:
> > > > > sailfish:/ # ls -LZ1 /proc/1/ns
> > > > > u:object_r:proc:s0 mnt
> > > > > u:object_r:proc:s0 net
> > > > > 
> > > > > On a device with the 4.9 kernel the have the "unlabeled" context:
> > > > > blueline:/ # ls -LZ1 /proc/1/ns
> > > > > u:object_r:unlabeled:s0 cgroup
> > > > > u:object_r:unlabeled:s0 mnt
> > > > > u:object_r:unlabeled:s0 net
> > > > 
> > > > First, ls -L dereferences symlinks so you are going to get the context
> > > > of the object referenced by the symlink, not the context of the symlink
> > > > itself.
> > > 
> > > I'm seeing a denial on the object not the symlink, so -L is what I want.
> > > 
> > > > 
> > > > Second, the task context is only assigned to proc inodes created via
> > > > proc_pid_make_inode(), which has never been the case of /proc/pid/ns
> > > > inodes - those have their own implementations and operations.
> > > > 
> > > > Third, /proc/pid/ns migrated from proc to its own pseudo filesystem,
> > > > nsfs, which requires a corresponding fs_use or genfscon rule in policy
> > > > or they will be unlabeled.  refpolicy has a genfscon rule. Confusingly
> > > > there appears to be both in Fedora policy, a fs_use_task and a genfscon
> > > > rule, and it appears that fs_use_task is being applied here.  I don't
> > > > know why or what exactly that means.  It won't be the task context for
> > > > the task associated with that /proc/pid directory but instead would be
> > > > whichever task context instantiates the inode.
> > > > 
> > > 
> > > So, how do I label these files in genfs_contexts?
> > > 
> > > "mount | grep nsfs" returns nothing.
> > 
> > # seinfo --genfs | grep nsfs
> >     genfscon nsfs /  sys.id:sys.role:fs.nsfs.fs:s0
> > 
> > Yes, i think this is a step backwards. In the past we got a nice list of objects that have no context associated when policy is loaded.
> > That list was removed. So sometimes its hard to determine whether something needs a genfscon if its not listen with `mount.
> 
> So, to be specific, commit 2088d60e3b2f53d0c9590a0202eeff85b288b1eb
> ("selinux: quiet the filesystem labeling behavior message") removed the
> logging of which filesystem labeling behavior was selected for each
> filesystem, and then the last remnant was dropped by commit
> 270e8573145a26de924e2dc644596332d400445b ("selinux: Remove redundant check
> for unknown labeling behavior").  The second commit makes sense given the
> prior one, but perhaps we do need/want to retain some kind of log message
> when mounting a filesystem that is not configured for labeling (i.e.
> SECURITY_FS_USE_NONE)?  We could add back a log message just for that case
> without reverting the other changes.

I would appreciate that, yes.

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Dominick Grift

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