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

[Stephen Smalley <sds@tycho.nsa.gov>]

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.

> 
>>
>>>
>>>>
>>>>>
>>>>>>
>>>>>>> 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
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>