Re: [PATCH v3] scripts/selinux: add basic mls support to mdp

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

Stephen Smalley <sds@tycho.nsa.gov> writes:

> On 2/15/19 11:52 AM, Dominick Grift wrote:
>> Stephen Smalley <sds@tycho.nsa.gov> writes:
>>
>>> On 2/15/19 10:25 AM, Stephen Smalley wrote:
>>>> On 2/15/19 10:05 AM, Stephen Smalley wrote:
>>>>> On 2/15/19 10:03 AM, Stephen Smalley wrote:
>>>>>> On 2/15/19 10:00 AM, Paul Moore wrote:
>>>>>>> On Fri, Feb 15, 2019 at 9:51 AM Stephen Smalley
>>>>>>> <sds@tycho.nsa.gov> wrote:
>>>>>>>> Add basic MLS policy support to mdp.  Declares
>>>>>>>> two sensitivities and two categories, defines
>>>>>>>> mls constraints for all permissions requiring
>>>>>>>> dominance (ala MCS), assigns the system-high
>>>>>>>> level to initial SID contexts and the default user
>>>>>>>> level, and assigns system-low level to filesystems.
>>>>>>>>
>>>>>>>> Also reworks the fs_use and genfscon rules to only
>>>>>>>> generate rules for filesystems that are configured
>>>>>>>> in the kernel.  In some cases this depends on a specific
>>>>>>>> config option for security xattrs, in other cases security
>>>>>>>> xattrs are unconditionally supported by a given filesystem
>>>>>>>> if the filesystem is enabled, and in some cases the filesystem
>>>>>>>> is always enabled in the kernel.  Dropped obsolete pseudo
>>>>>>>> filesystems.
>>>>>>>>
>>>>>>>> NB The list of fs_use_* and genfscon rules emitted by mdp
>>>>>>>> is very incomplete compared to refpolicy or Android sepolicy.
>>>>>>>> We should probably expand it.
>>>>>>>>
>>>>>>>> Usage:
>>>>>>>> scripts/selinux/mdp/mdp -m policy.conf file_contexts
>>>>>>>> checkpolicy -M -o policy policy.conf
>>>>>>>>
>>>>>>>> Then install the resulting policy and file_contexts as usual.
>>>>>>>>
>>>>>>>> Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
>>>>>>>> ---
>>>>>>>> v3 fixes up the file contexts generation code to also use
>>>>>>>> SYSTEMLOW and
>>>>>>>> collapse down to a single fprintf call per line.
>>>>>>>>    scripts/selinux/mdp/mdp.c | 131
>>>>>>>> ++++++++++++++++++++++++++++++--------
>>>>>>>>    1 file changed, 103 insertions(+), 28 deletions(-)
>>>>>>>
>>>>>>> This is great Stephen, thanks for working on this - and rather quickly
>>>>>>> too!  For those who don't follow the GitHub issues, I just opened an
>>>>>>> issue yesterday mentioning it would be nice to add MLS support to the
>>>>>>> mdp tool.
>>>>>>>
>>>>>>> Are you planning to keep playing with this?  I'm asking not because I
>>>>>>> think it needs more work to be worthwhile, but rather I don't want to
>>>>>>> merge something that you want to continue working on.  If you are
>>>>>>> happy with this latest patch I think it is okay to merge this into
>>>>>>> selinux/next, even at this late stage, simply because it is not part
>>>>>>> of a built kernel, but rather a developer's tool.
>>>>>>
>>>>>> No, I think I'm done for now unless you find a problem with
>>>>>> it. Absent some compelling use case for mdp it is hard to justify
>>>>>> spending any more time on it.
>>>>>
>>>>> Note however that the instructions in
>>>>> Documentation/admin-guide/LSM/SELinux.rst just say to run
>>>>> scripts/selinux/install_policy.sh and since that doesn't pass -m to
>>>>> mdp or -M to checkpolicy, no one will use this support unless they
>>>>> do it all by hand.
>>>>
>>>> FWIW, a Fedora system wouldn't come up cleanly with this policy.
>>>> Partly appears to be due to systemd having embedded security
>>>> contexts specific to Fedora/refpolicy into its own configurations
>>>> and partly due to MLS denials.  I don't even know if it would work
>>>> before this change though...
>>>
>>> Couldn't seem to get a mdp-generated policy to boot on Fedora even in
>>> permissive, before or after this change.  I assume it has to do with
>>> leaking of contexts outside of the policy and/or missing config files
>>> from the dummy policy (e.g. /etc/selinux/targeted/contexts/ has
>>> systemd_contexts and other userspace config files that don't exist in
>>> the mdp policy).  More evidence of the irrelevance of mdp...
>>
>> Oh, right you need a "dbus_contexts" file probably. DBUS refuses to
>> start without it, and these day's without dbus no system
>
> There is actually a dbus_contexts file provided for mdp
> (scripts/selinux/mdp/dbus_contexts) but not a systemd_contexts or any
> other *_contexts files besides file_contexts.

There is no systemd_contexts, that never made it through. any references
to that in libsemanage can be removed.

I suppose it might be related to no dbus and systemd access vector
support. maybe that upsets dbus and/or systemd

>
>>
>>>
>>>>
>>>>>
>>>>>>
>>>>>>>
>>>>>>>> diff --git a/scripts/selinux/mdp/mdp.c b/scripts/selinux/mdp/mdp.c
>>>>>>>> index 073fe7537f6c..4223e2fea441 100644
>>>>>>>> --- a/scripts/selinux/mdp/mdp.c
>>>>>>>> +++ b/scripts/selinux/mdp/mdp.c
>>>>>>>> @@ -33,6 +33,7 @@
>>>>>>>>    #include <unistd.h>
>>>>>>>>    #include <string.h>
>>>>>>>>    #include <sys/socket.h>
>>>>>>>> +#include <linux/kconfig.h>
>>>>>>>>
>>>>>>>>    static void usage(char *name)
>>>>>>>>    {
>>>>>>>> @@ -95,10 +96,31 @@ int main(int argc, char *argv[])
>>>>>>>>           }
>>>>>>>>           fprintf(fout, "\n");
>>>>>>>>
>>>>>>>> -       /* NOW PRINT OUT MLS STUFF */
>>>>>>>> +       /* print out mls declarations and constraints */
>>>>>>>>           if (mls) {
>>>>>>>> -               printf("MLS not yet implemented\n");
>>>>>>>> -               exit(1);
>>>>>>>> +               fprintf(fout, "sensitivity s0;\n");
>>>>>>>> +               fprintf(fout, "sensitivity s1;\n");
>>>>>>>> +               fprintf(fout, "dominance { s0 s1 }\n");
>>>>>>>> +               fprintf(fout, "category c0;\n");
>>>>>>>> +               fprintf(fout, "category c1;\n");
>>>>>>>> +               fprintf(fout, "level s0:c0.c1;\n");
>>>>>>>> +               fprintf(fout, "level s1:c0.c1;\n");
>>>>>>>> +#define SYSTEMLOW "s0"
>>>>>>>> +#define SYSTEMHIGH "s1:c0.c1"
>>>>>>>> +               for (i = 0; secclass_map[i].name; i++) {
>>>>>>>> +                       struct security_class_mapping *map =
>>>>>>>> &secclass_map[i];
>>>>>>>> +
>>>>>>>> +                       fprintf(fout, "mlsconstrain %s {\n",
>>>>>>>> map->name);
>>>>>>>> +                       for (j = 0; map->perms[j]; j++)
>>>>>>>> +                               fprintf(fout, "\t%s\n",
>>>>>>>> map->perms[j]);
>>>>>>>> +                       /*
>>>>>>>> +                        * This requires all subjects and
>>>>>>>> objects to be
>>>>>>>> +                        * single-level (l2 eq h2), and that the
>>>>>>>> subject
>>>>>>>> +                        * level dominate the object level (h1 dom h2)
>>>>>>>> +                        * in order to have any permissions to it.
>>>>>>>> +                        */
>>>>>>>> +                       fprintf(fout, "} (l2 eq h2 and h1 dom
>>>>>>>> h2);\n\n");
>>>>>>>> +               }
>>>>>>>>           }
>>>>>>>>
>>>>>>>>           /* types, roles, and allows */
>>>>>>>> @@ -108,34 +130,87 @@ int main(int argc, char *argv[])
>>>>>>>>           for (i = 0; secclass_map[i].name; i++)
>>>>>>>>                   fprintf(fout, "allow base_t base_t:%s *;\n",
>>>>>>>>                           secclass_map[i].name);
>>>>>>>> -       fprintf(fout, "user user_u roles { base_r };\n");
>>>>>>>> -       fprintf(fout, "\n");
>>>>>>>> +       fprintf(fout, "user user_u roles { base_r }");
>>>>>>>> +       if (mls)
>>>>>>>> +               fprintf(fout, " level %s range %s - %s", SYSTEMHIGH,
>>>>>>>> +                       SYSTEMLOW, SYSTEMHIGH);
>>>>>>>> +       fprintf(fout, ";\n");
>>>>>>>> +
>>>>>>>> +#define USERROLETYPE "user_u:base_r:base_t"
>>>>>>>>
>>>>>>>>           /* default sids */
>>>>>>>>           for (i = 1; i < initial_sid_to_string_len; i++)
>>>>>>>> -               fprintf(fout, "sid %s user_u:base_r:base_t\n",
>>>>>>>> initial_sid_to_string[i]);
>>>>>>>> +               fprintf(fout, "sid %s " USERROLETYPE "%s\n",
>>>>>>>> +                       initial_sid_to_string[i], mls ? ":"
>>>>>>>> SYSTEMHIGH : "");
>>>>>>>>           fprintf(fout, "\n");
>>>>>>>>
>>>>>>>> -       fprintf(fout, "fs_use_xattr ext2 user_u:base_r:base_t;\n");
>>>>>>>> -       fprintf(fout, "fs_use_xattr ext3 user_u:base_r:base_t;\n");
>>>>>>>> -       fprintf(fout, "fs_use_xattr ext4 user_u:base_r:base_t;\n");
>>>>>>>> -       fprintf(fout, "fs_use_xattr jfs user_u:base_r:base_t;\n");
>>>>>>>> -       fprintf(fout, "fs_use_xattr xfs user_u:base_r:base_t;\n");
>>>>>>>> -       fprintf(fout, "fs_use_xattr reiserfs
>>>>>>>> user_u:base_r:base_t;\n");
>>>>>>>> -       fprintf(fout, "fs_use_xattr jffs2 user_u:base_r:base_t;\n");
>>>>>>>> -       fprintf(fout, "fs_use_xattr gfs2 user_u:base_r:base_t;\n");
>>>>>>>> -
>>>>>>>> -       fprintf(fout, "fs_use_task eventpollfs
>>>>>>>> user_u:base_r:base_t;\n");
>>>>>>>> -       fprintf(fout, "fs_use_task pipefs user_u:base_r:base_t;\n");
>>>>>>>> -       fprintf(fout, "fs_use_task sockfs user_u:base_r:base_t;\n");
>>>>>>>> -
>>>>>>>> -       fprintf(fout, "fs_use_trans mqueue user_u:base_r:base_t;\n");
>>>>>>>> -       fprintf(fout, "fs_use_trans devpts user_u:base_r:base_t;\n");
>>>>>>>> -       fprintf(fout, "fs_use_trans hugetlbfs
>>>>>>>> user_u:base_r:base_t;\n");
>>>>>>>> -       fprintf(fout, "fs_use_trans tmpfs user_u:base_r:base_t;\n");
>>>>>>>> -       fprintf(fout, "fs_use_trans shm user_u:base_r:base_t;\n");
>>>>>>>> -
>>>>>>>> -       fprintf(fout, "genfscon proc / user_u:base_r:base_t\n");
>>>>>>>> +#define FS_USE(behavior, fstype)                           \
>>>>>>>> +       fprintf(fout, "fs_use_%s %s " USERROLETYPE "%s;\n", \
>>>>>>>> +               behavior, fstype, mls ? ":" SYSTEMLOW : "")
>>>>>>>> +
>>>>>>>> +       /*
>>>>>>>> +        * Filesystems whose inode labels can be fetched via getxattr.
>>>>>>>> +        */
>>>>>>>> +#ifdef CONFIG_EXT2_FS_SECURITY
>>>>>>>> +       FS_USE("xattr", "ext2");
>>>>>>>> +#endif
>>>>>>>> +#ifdef CONFIG_EXT3_FS_SECURITY
>>>>>>>> +       FS_USE("xattr", "ext3");
>>>>>>>> +#endif
>>>>>>>> +#ifdef CONFIG_EXT4_FS_SECURITY
>>>>>>>> +       FS_USE("xattr", "ext4");
>>>>>>>> +#endif
>>>>>>>> +#ifdef CONFIG_JFS_SECURITY
>>>>>>>> +       FS_USE("xattr", "jfs");
>>>>>>>> +#endif
>>>>>>>> +#ifdef CONFIG_REISERFS_FS_SECURITY
>>>>>>>> +       FS_USE("xattr", "reiserfs");
>>>>>>>> +#endif
>>>>>>>> +#ifdef CONFIG_JFFS2_FS_SECURITY
>>>>>>>> +       FS_USE("xattr", "jffs2");
>>>>>>>> +#endif
>>>>>>>> +#ifdef CONFIG_XFS_FS
>>>>>>>> +       FS_USE("xattr", "xfs");
>>>>>>>> +#endif
>>>>>>>> +#ifdef CONFIG_GFS2_FS
>>>>>>>> +       FS_USE("xattr", "gfs2");
>>>>>>>> +#endif
>>>>>>>> +
>>>>>>>> +       /*
>>>>>>>> +        * Filesystems whose inodes are labeled from allocating task.
>>>>>>>> +        */
>>>>>>>> +       FS_USE("task", "pipefs");
>>>>>>>> +       FS_USE("task", "sockfs");
>>>>>>>> +#ifdef CONFIG_POSIX_MQUEUE
>>>>>>>> +       FS_USE("task", "mqueue");
>>>>>>>> +#endif
>>>>>>>> +
>>>>>>>> +       /*
>>>>>>>> +        * Filesystems whose inode labels are computed from both
>>>>>>>> +        * the allocating task and the superblock label.
>>>>>>>> +        */
>>>>>>>> +#ifdef CONFIG_UNIX98_PTYS
>>>>>>>> +       FS_USE("trans", "devpts");
>>>>>>>> +#endif
>>>>>>>> +#ifdef CONFIG_HUGETLBFS
>>>>>>>> +       FS_USE("trans", "hugetlbfs");
>>>>>>>> +#endif
>>>>>>>> +#ifdef CONFIG_TMPFS
>>>>>>>> +       FS_USE("trans", "tmpfs");
>>>>>>>> +#endif
>>>>>>>> +
>>>>>>>> +
>>>>>>>> +#define GENFSCON(fstype, prefix)                            \
>>>>>>>> +       fprintf(fout, "genfscon %s %s " USERROLETYPE "%s\n", \
>>>>>>>> +               fstype, prefix, mls ? ":" SYSTEMLOW : "")
>>>>>>>> +
>>>>>>>> +       /*
>>>>>>>> +        * Filesystems whose inodes are labeled from path prefix match
>>>>>>>> +        * relative to the filesystem root.  Depending on the
>>>>>>>> filesystem,
>>>>>>>> +        * only a single label for all inodes may be supported.
>>>>>>>> +        */
>>>>>>>> +       GENFSCON("proc", "/");
>>>>>>>> +       GENFSCON("selinuxfs", "/");
>>>>>>>>
>>>>>>>>           fclose(fout);
>>>>>>>>
>>>>>>>> @@ -144,8 +219,8 @@ int main(int argc, char *argv[])
>>>>>>>>                   printf("Wrote policy, but cannot open %s for
>>>>>>>> writing\n", ctxout);
>>>>>>>>                   usage(argv[0]);
>>>>>>>>           }
>>>>>>>> -       fprintf(fout, "/ user_u:base_r:base_t\n");
>>>>>>>> -       fprintf(fout, "/.* user_u:base_r:base_t\n");
>>>>>>>> +       fprintf(fout, "/ " USERROLETYPE "%s\n", mls ? ":"
>>>>>>>> SYSTEMLOW : "");
>>>>>>>> +       fprintf(fout, "/.* " USERROLETYPE "%s\n", mls ? ":"
>>>>>>>> SYSTEMLOW : "");
>>>>>>>>           fclose(fout);
>>>>>>>>
>>>>>>>>           return 0;
>>>>>>>> -- 
>>>>>>>> 2.20.1
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>

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Dominick Grift