Messages in this thread | | | Date | Thu, 9 Mar 2017 18:28:15 +0100 | From | Greg KH <> | Subject | Re: [Regression?] 1ea0ce4069 ("selinux: allow changing labels for cgroupfs") stops Android from booting |
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On Mon, Feb 27, 2017 at 04:23:28PM -0500, Stephen Smalley wrote: > On Mon, 2017-02-27 at 12:48 -0800, Nick Kralevich wrote: > > On Mon, Feb 27, 2017 at 11:53 AM, Stephen Smalley <sds@tycho.nsa.gov> > > wrote: > > > > > > > > > > > I can reproduce it on angler (with a back-port of just that > > > > patch), > > > > although I am unclear on the cause. The patch is only supposed > > > > to > > > > enable explicit setting of security labels by userspace on cgroup > > > > files, so it isn't supposed to cause any breakage under existing > > > > policy. Prior to the patch, the kernel would always just return > > > > -1 > > > > with errno EOPNOTSUPP upon attempts to set security labels on > > > > cgroup > > > > files; with the patch, the kernel may instead return -1 with > > > > errno > > > > EACCES if not allowed. So I suppose if userspace was explicitly > > > > testing for EOPNOTSUPP and not failing hard in that case, it > > > > might > > > > cause breakage. Not sure why existing userspace would be trying > > > > to > > > > relabel cgroup files, unless it is just a recursive restorecon > > > > that > > > > happens to traverse into a cgroup mount (and in that case, not > > > > sure > > > > why > > > > it would be fatal). Other possible interaction would be use of > > > > setfscreatecon() prior to creating a file in cgroup. > > > > > > Oh, I see - it is the latter. > > > > > > For example, init.rc does mkdir /dev/cpuctl/bg_non_interactive, > > > which > > > internally looks up the context for that directory from > > > file_contexts > > > and does a setfscreatecon() followed by a mkdir(). Previously, > > > that > > > was ignored because cgroup did not support anything other than the > > > policy-defined label. But now it will try to use that label, which > > > in > > > turn will trigger a denial in enforcing mode and the create will > > > fail. > > > > > > So this is an incompatible change and needs to be reverted. > > > We'll need to wrap it up with a policy capability or something to > > > allow > > > it to be enabled only if the policy correctly supports it. Even > > > better, we should instead just allow the policy to specify which > > > filesystems should support this behavior (already on the issues > > > list). > > > > > > > If Android is the only system affected by this bug, I would prefer to > > just fix Android to allow for this patch, rather than having > > additional kernel complexity. > > Well, it does break userspace (even if it happens to only affect > Android, which isn't clear, e.g. possibly a distribution would likewise > suffer breakage under a tighter policy), and we already have a long- > standing open issue to replace the current set of whitelisted > filesystem types with something configuration-driven. So I'm ok with > reverting it and requiring it to be done in a more general way. The > latter is something we want regardless. >
Please revert this, it's not ok to break working userspace code. I've gotten a few off-line queries as to why this ended up being merged when it was known to break Android.
thanks,
greg k-h
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