Background:
We are using eCryptfs as a way to encrypt directories as well as PID namespaces
as a way to isolate processes. We've created
native processes that run in different namespaces and need to mount/unmount
directories.
We've allowed eCryptfs to use xattributes with fs_use_xattr:
e.g.
fs_use_xattr ecryptfs u:object_r:labeledfs:s0;
And we've added allows for native daemons to mount/unmount directories:
e.g.
allow namespaceinit labeledfs:filesystem remount;
allow namespaceservice labeledfs:filesystem mount;
allow namespaceservice labeledfs:filesystem unmount;
This led us to need to add exceptions in certain neverallow statements:
e.g. external/sepolicy/domain.te (added -namespaceinit -namespaceservice
-labeledfs)
neverallow { domain -kernel -init -recovery -vold -zygote -namespaceinit
-namespaceservice } { fs_type -sdcard_type -labeledfs }:filesystem { mount
remount relabelfrom relabelto };
However, CDD is extremely restrictive on making any changes to neverallows:
● MUST NOT modify, omit, or replace the neverallowrules present within the
sepolicyfile provided in the upstream Android Open Source Project (AOSP) and
the policy MUST compile with all neverallowpresent, for both AOSP SELinux
domains as well as device/vendorspecific domains
We could argue that we are not weakening security, but making security
improvements to the system with new encryption and isolation mechanisms.
We understand the spirit of these clauses in the CDD is to not allow the
security to degrade; however, these recent CDD statements are hand-cuffing us
from adding new security features.
Questions:
1. Is there any SELinux way to get around us changing the neverallows? (e.g.
creative labeling? sub-typing? are we stuck with the current labeling?)
2. Is there any negotiation process for statements in the CDD? What steps can
we take?
3. Other ideas?
Thanks,
Cliff
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