[refpolicy] file map perm issues

[Jason Zaman]

Hey all,

So kernel 4.13 was just released which contains the file map stuff and
I've run into a fair few issues. I'd like some discussion about naming
and how to best apply the perm.

we currently have a bunch of interfaces like "*_read_*_files", eg:
files_read_etc_files, files_rw_etc_files, files_manage_etc_files.
should interfaces like this include the map perm? I am thinking no?
Or maybe included for domains that seem to always need it (eg etc_t) and
not by default?

we also have these defs file_read_perms file_mmap_perms. so since those
are different I'm thinking that files_read_etc_files should also be
separated like that?

If they are to be separated, should things be just plain
allow ...:file map; or should it just use file mmap_file_perms;? The
issue with this one is that mmap_file_perms includes the execute perm.
If we should just use mmap_file_perms, then maybe the defs should be
changed like this:

-define(`mmap_file_perms',`{ getattr open map read execute ioctl }')
+define(`mmap_file_perms',`{ getattr open map read ioctl }')
 define(`exec_file_perms',`{ getattr open map read execute ioctl execute_no_trans }')

Isnt execute generally a more risky perm? also manage_file_perms and
write_ and rw_ defs currently dont give the map perm, should they?


Once that is decided, what should interfaces for map interfaces look
like? just map? should *_map_*_files interfaces include include read and
open and stuff too ro are people expected to just use both interfaces
together?

########################################
## <summary>
##     Map user tmpfs files.
## </summary>
## <param name="domain">
##     <summary>
##     Domain allowed access.
##     </summary>
## </param>
#
interface(`userdom_map_user_tmpfs_files',`
       gen_require(`
               type user_tmpfs_t;
       ')

       allow $1 user_tmpfs_t:file map;
')


Lastly, Ive seen a whole ton of domains need allow foo etc_t:file map;
and the audit logs show /etc/passwd as the file being accessed.  I'm
fairly certain this is from nsswitch. Can someone else verify too?
strace (below) and the fact that there is a very strong correlation with
domains that contain nsswitch_domain.

authlogin.te already contains: files_read_etc_files(nsswitch_domain), so
if we just add file map to the _read_ interfaces then it'll just work.
otherwise adding a files_mmap_etc_files(nsswitch_domain) would work.

excerpt of relevant lines:
$ strace whoami
read(3, "# /etc/nsswitch.conf:\n# $Header:"..., 512) = 508
open("/lib64/libnss_nis.so.2", O_RDONLY|O_CLOEXEC) = 3
open("/lib64/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = 3
open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
mmap(NULL, 2305, PROT_READ, MAP_SHARED, 3, 0) = 0x7fa04654f000

I'm going to test out these fixes more and will send patches once style
has been decided.

-- Jason