[SSSD] [PATCHES] SELinux processing related patches

Jakub Hrozek jhrozek at redhat.com
Mon Mar 18 11:03:41 UTC 2013


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..

> +    if (file_content == NULL) {
> +        ret = ENOMEM;
> +        goto done;
> +    }



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