On Fri, 2017-04-07 at 11:39 -0700, Nick Kralevich wrote: > When a file is created in a directory, the default label for the file > is based on the label of the enclosing directory (unless something > like setfscreatecon is used). For example: > > bullhead:/ # cd /data/misc/zoneinfo/ > > bullhead:/data/misc/zoneinfo # ls -ladZ . > drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096 > 1971-06-19 17:07 . > bullhead:/data/misc/zoneinfo # touch asdf > bullhead:/data/misc/zoneinfo # ls -ladZ . asdf > > drwxrwxr-x 2 system system u:object_r:zoneinfo_data_file:s0 4096 > 2017-04-07 18:32 . > -rw-rw-rw- 1 root root u:object_r:zoneinfo_data_file:s0 0 > 2017-04-07 18:32 asdf > > note how the label of the "asdf" file matches the label of the > enclosing directory. > > However, that's not true when the directory uses categories. In that > case, the newly created file inherits the label, but not the > categories. For example: > > bullhead:/data/data # cd /data/data/com.android.chrome > bullhead:/data/data/com.android.chrome # ls -ladZ . > drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768 4096 > 1971-07-15 15:31 . > bullhead:/data/data/com.android.chrome # touch asdf > bullhead:/data/data/com.android.chrome # ls -laZd . asdf > drwx------ 6 u0_a60 u0_a60 u:object_r:app_data_file:s0:c512,c768 4096 > 2017-04-07 18:35 . > -rw-rw-rw- 1 root root u:object_r:app_data_file:s0 0 > 2017-04-07 18:35 asdf > > Note how the label is maintained, but the "c512,c768" portion is not > maintained. While this example occurs when I'm running in a > permissive > domain, it also occurs in an enforcing domain. > > The inconsistency seems weird, and I'm sure there's a good reason why > this occurs that I'm not familiar with. Can someone help me > understand > if this is expected, and if so, why? First, the good news is that you get to specify which behavior you want for each context field and object class through policy (as long as your kernel and policy version supports it), see: https://selinuxproject.org/page/DefaultRules Second, there are different defaults for each of the fields of the security contexts based on what is most normative for that particular security model. The user identity defaults to that of the creating process since we typically do not allow a process to create files with a different user identity and want the file to reflect its creator (this is defined through constraints on user identity in policies that define more than one, unlike Android). The role defaults to the fixed object_r role because originally we didn't envision a use case for roles on files. The MLS range defaults to the low/current level of the process because a process is typically not allowed to create files at a different level and we want the file to reflect the sensitivity of the data which originated from the process. The type defaults to a related object type (in this case that of the parent directory) because process domains and object types are separate (aside from overlapping use for /proc/pid) and the relationships among them are explicit through the TE rules / access matrix rather than through implicit rules. Of course, in addition to being able to globally configure the default behavior, you can also customize specific cases through the role/type/range_transition rules. With your example above, you wanted the file to inherit the level of the directory, but consider the situation where a process with categories (:s0:c512,c768) creates a file in some shared (mlstrustedobject) directory that is just :s0. Do you want that file to end up as just :s0? In the MLS world, that would be a downgrade / info leak. _______________________________________________ Selinux mailing list Selinux@xxxxxxxxxxxxx To unsubscribe, send email to Selinux-leave@xxxxxxxxxxxxx. To get help, send an email containing "help" to Selinux-request@xxxxxxxxxxxxx.
