[SSSD] [PATCHES] SELinux processing related patches

Michal Židek mzidek at redhat.com
Tue Mar 19 16:15:39 UTC 2013


On 03/19/2013 03:23 PM, Jakub Hrozek wrote:
> On Mon, Mar 18, 2013 at 03:32:45PM +0100, Michal Židek wrote:
>> On 03/18/2013 12:03 PM, Jakub Hrozek wrote:
>>> On Fri, Mar 08, 2013 at 09:10:24PM +0100, Michal Židek wrote:
>>>>> On Mon, Mar 04, 2013 at 04:13:31PM +0100, Michal Židek wrote:
>>>>>> On 03/04/2013 02:53 PM, Pavel Březina wrote:
>>>>>>> On 03/01/2013 04:13 PM, Michal Židek wrote:
>>>>>>>> Patch 1: Right now, we have SELinux procesing split between the provider
>>>>>>>> and responder. This patch moves it to provider only. So no partial
>>>>>>>> results are sent to responder for further processing, which makes the
>>>>>>>> processing steps easier to follow. (Originally the idea was to move the
>>>>>>>> processing to the responder, but completely removing the procesing from
>>>>>>>> provider and let it just update db turned to be more invasive than
>>>>>>>> completely removing the procesing from responder.) If this patch is
>>>>>>>> accepted, SELinux policy needs to be modified to allow sssd_be to write
>>>>>>>> the selinux login files.
>>>>>>>> https://fedorahosted.org/sssd/ticket/1743
>>>>>>>>
>>>>>
>>>>> Even though we would have to tailor the SELinux policy, I'm not opposed
>>>>> to moving the logic to provider. Originally I proposed responder because
>>>>> I simply wanted all the processing to happen on one place.
>>>>>
>>>>> The whole intent of the refactor is to get rid of passing some
>>>>> information from provider by writing data to sysdb in provider and
>>>>> reading them in responder. If we get rid of that architectural bug, I'm
>>>>> fine with any solution.
>>>>>
>>>>> FWIW, the other alternative that we were discussing with Michal was to
>>>>> done the processing in provider and then send the resulting string to
>>>>> responder via DBus. But it seemed kind of pointless to send the result
>>>>> with DBus just to avoid moving the write of the file.
>>>>>
>>>>>>>>
>>>>>>>> Patch 2, 3: Reuse cached selinux maps. Patch 2 shows how it is done with
>>>>>>>> refresh interval fixed to 120 seconds. Patch 3 adds ipa option to
>>>>>>>> configure this interval (I didn't want to merge these patches for better
>>>>>>>> readability). Default value is 30 seconds.
>>>>>>>> https://fedorahosted.org/sssd/ticket/1744
>>>>>>>>
>>>>>>>>
>>>>>>>> Patches are attached.
>>>>>>>>
>>>>>>>> Thanks
>>>>>>>> Michal
>>>>>>>
>>>>>>> Hi,
>>>>>>> switch the order of the second and third patch. So the flow is: add new
>>>>>>> option, then use it.
>>>>>>
>>>>>> I don't think this is good idea. If the option is present, the logic
>>>>>> to implement it's effect should be present too. It is also easier to
>>>>>> test the patches one by one this way (first test the mechanism with
>>>>>> fixed time interval, then make it configurable and test if interval
>>>>>> is changing). For now I only changed the 120 seconds in the 2nd
>>>>>> patch to 5 seconds (so it is not that aggressive).
>>>>>>>
>>>>>>> Do we want to use it anyway? Shouldn't be SELinux maps always updated?
>>>>>>>
>>>>>>
>>>>>> Well, we can still make 0 seconds the default value (or 5 seconds,
>>>>>> which is used by IPA_HBAC_REFRESH). But selinux maps are not changed
>>>>>> frequently on ipa side, so having this option is IMO good thing. In
>>>>>> the new attached patches the default value is changed to 5.
>>>>>>
>>>>>> Michal
>>>>>
>>>>> Good start, but a nack, sorry.
>>>>>
>>>>> I'm seeing a segfaut and valgrind says it's becuase of a user-after-free
>>>>> bug:
>>>>> ==28566== Invalid read of size 4
>>>>> ==28566==    at 0x5264CFE: sysdb_attrs_get_el_ext (sysdb.c:313)
>>>>> ==28566==    by 0x5264EC6: sysdb_attrs_get_string (sysdb.c:356)
>>>>> ==28566==    by 0x5280A75: sysdb_store_selinux_entity (sysdb_selinux.c:102)
>>>>> ==28566==    by 0x528153D: sysdb_store_selinux_usermap (sysdb_selinux.c:181)
>>>>> ==28566==    by 0x122AABE0: ipa_save_user_maps (ipa_selinux_common.c:48)
>>>>> ==28566==    by 0x122A55E1: ipa_selinux_handler_done (ipa_selinux.c:260)
>>>>> ==28566==    by 0x122A9943: ipa_get_selinux_maps_done (ipa_selinux.c:1149)
>>>>> ==28566==    by 0x122AA8DB: ipa_selinux_get_maps_done (ipa_selinux_maps.c:203)
>>>>> ==28566==    by 0x12E2995C: sdap_get_generic_done (sdap_async.c:1558)
>>>>> ==28566==    by 0x12E29132: sdap_get_generic_ext_done (sdap_async.c:1449)
>>>>> ==28566==    by 0x12E2204B: sdap_process_message (sdap_async.c:366)
>>>>> ==28566==    by 0x12E21593: sdap_process_result (sdap_async.c:209)
>>>>> ==28566==  Address 0x17e416a0 is 80 bytes inside a block of size 96 free'd
>>>>> ==28566==    at 0x4C297A6: free (vg_replace_malloc.c:446)
>>>>> ==28566==    by 0x56E2880: _talloc_free_internal (talloc.c:876)
>>>>> ==28566==    by 0x122A5BB6: ipa_selinux_process_maps (ipa_selinux.c:355)
>>>>> ==28566==    by 0x122A4FFF: ipa_selinux_handler_done (ipa_selinux.c:224)
>>>>> ==28566==    by 0x122A9943: ipa_get_selinux_maps_done (ipa_selinux.c:1149)
>>>>> ==28566==    by 0x122AA8DB: ipa_selinux_get_maps_done (ipa_selinux_maps.c:203)
>>>>> ==28566==    by 0x12E2995C: sdap_get_generic_done (sdap_async.c:1558)
>>>>> ==28566==    by 0x12E29132: sdap_get_generic_ext_done (sdap_async.c:1449)
>>>>> ==28566==    by 0x12E2204B: sdap_process_message (sdap_async.c:366)
>>>>> ==28566==    by 0x12E21593: sdap_process_result (sdap_async.c:209)
>>>>> ==28566==    by 0x12E20BE5: sdap_ldap_next_result (sdap_async.c:159)
>>>>> ==28566==    by 0x54DAD3F: tevent_common_loop_timer_delay (in /usr/lib64/libtevent.so.0.9.17)
>>>>>
>>>>> Other tests passed, the use-after-free happens when there is a specific
>>>>> mapping rule only:
>>>>>
>>>>>     Rule name: test_user1_specific_host
>>>>>     SELinux User: staff_u:s0-s0:c0.c1023
>>>>>     Enabled: TRUE
>>>>>     Users: tuser3
>>>>>     Hosts: client.example.com
>>>>>
>>>>
>>>> Fixed.
>>>>
>>>>> The code looks OK to me, I would just change two things:
>>>>> 1) Split the function prepare_selinux_file_content() into one that
>>>>> creates the order array and one that evaluates the matched rules based
>>>>> on the order. Currently the function does two different tasks and is too
>>>>> long.
>>>>>
>>>>> 2) Rename the prepare_selinux_file_content() function so that it is
>>>>> clear it picks a single rule from a set of rules with same priority
>>>>> based on the configured order.
>>>>>
>>>>
>>>> I split the function into two new functions (create_order_array,
>>>> choose_best_seuser) and added some comments.
>>>>
>>>> New patches attached.
>>>>
>>>> Thanks
>>>> Michal
>>>
>>> Nack,
>>>
>>>> +/* Choose best selinux user based on given order and write
>>>> + * the user to selinux login file. */
>>>> +static errno_t choose_best_seuser(struct sysdb_attrs **usermaps,
>>>> +                                  struct pam_data *pd,
>>>> +                                  char **order_array, int order_count,
>>>> +                                  const char *default_user)
>>>> +{
>>>> +    TALLOC_CTX *tmp_ctx;
>>>> +    char *file_content = NULL;
>>>> +    const char *tmp_str;
>>>> +    errno_t ret, err;
>>>> +    int i, j;
>>>> +
>>>> +    /* If no maps match, we'll use the default SELinux user from the
>>>> +     * config */
>>>> +    file_content = talloc_strdup(tmp_ctx, default_user);
>>>
>>> This is clearly wrong, tmp_ctx is never assigned to. The code may work
>>> only by chance without optimizations becaues tmp_ctx would have been NULL..
>>>
>>
>> Good catch. Sorry for that.
>>
>>>> +    if (file_content == NULL) {
>>>> +        ret = ENOMEM;
>>>> +        goto done;
>>>> +    }
>>
>> I also changed the behaviour if HAVE_SELINUX_LOGIN_DIR is not defined.
>> In that case, the processing is skipped and the ipa_selinux_handler just
>> returns success.
>>
>> New patches attached.
>>
>> Thanks
>> Michal
>
> All my tests passed now. Ack.
>
> Please open a bug in Fedora against selinux-policy-targeted asking them
> to allow sssd_be to write to the logins directory. It would be best to
> paste them the complete AVC.

RHEL7 bug https://bugzilla.redhat.com/show_bug.cgi?id=923354
Fedora bug: https://bugzilla.redhat.com/show_bug.cgi?id=923347

Michal




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