Re: ldap_set_option() performs blocking name resolution during initalization

[Jakub Hrozek <jakub.hrozek@gmail.com>]

On Wed, 2014-06-11 at 08:41 +0200, Jan Synacek wrote:
> Is it intentional? If yes, could you please explain why, or point me to
> a documentation where I can find the answer?
> 
> A backtrace and a snippet of code follow:
> 
> #0  0x00007fda39c80a70 in __poll_nocancel () at ../sysdeps/unix/syscall-template.S:81
> #1  0x00007fda38d17e0d in send_dg (resplen2=0x0, anssizp2=0x0, ansp2=0x0, 
>     anscp=0x7fff2548cb30, gotsomewhere=<synthetic pointer>, 
>     v_circuit=<synthetic pointer>, ns=0, terrno=0x7fff2548bab0, anssizp=0x7fff2548bbf0, 
>     ansp=0x7fff2548baa8, buflen2=0, buf2=0x0, buflen=36, buf=0x7fff2548bc20 "\tg\001", 
>     statp=0x7fda39f533e0 <_res@GLIBC_2.2.5>) at res_send.c:1059
> #2  __libc_res_nsend (statp=statp@entry=0x7fda39f533e0 <_res@GLIBC_2.2.5>, 
>     buf=buf@entry=0x7fff2548bc20 "\tg\001", buflen=<optimized out>, buf2=buf2@entry=0x0, 
>     buflen2=buflen2@entry=0, ans=ans@entry=0x7fff2548c700 "", anssiz=anssiz@entry=1024, 
>     ansp=ansp@entry=0x7fff2548cb30, ansp2=ansp2@entry=0x0, nansp2=nansp2@entry=0x0, 
>     resplen2=resplen2@entry=0x0) at res_send.c:556
> #3  0x00007fda38d15d47 in __GI___libc_res_nquery (
>     statp=statp@entry=0x7fda39f533e0 <_res@GLIBC_2.2.5>, 
>     name=0x7fff2548d140 "client.example.com", class=class@entry=1, type=type@entry=1, 
>     answer=answer@entry=0x7fff2548c700 "", anslen=anslen@entry=1024, 
>     answerp=answerp@entry=0x7fff2548cb30, answerp2=answerp2@entry=0x0, 
>     nanswerp2=nanswerp2@entry=0x0, resplen2=resplen2@entry=0x0) at res_query.c:226
> #4  0x00007fda38d16963 in __libc_res_nquerydomain (domain=0x0, resplen2=0x0, 
>     nanswerp2=0x0, answerp2=0x0, answerp=0x7fff2548cb30, anslen=1024, 
>     answer=0x7fff2548c700 "", type=1, class=1, name=0x7fff2548d140 "client.example.com", 
>     statp=0x7fda39f533e0 <_res@GLIBC_2.2.5>) at res_query.c:582
> #5  __GI___libc_res_nsearch (statp=0x7fda39f533e0 <_res@GLIBC_2.2.5>, 
>     name=name@entry=0x7fff2548d140 "client.example.com", class=class@entry=1, 
>     type=type@entry=1, answer=answer@entry=0x7fff2548c700 "", anslen=anslen@entry=1024, 
>     answerp=0x7fff2548cb30, answerp2=answerp2@entry=0x0, nanswerp2=nanswerp2@entry=0x0, 
>     resplen2=resplen2@entry=0x0) at res_query.c:378
> #6  0x00007fda2f2777e4 in __GI__nss_dns_gethostbyname3_r (
>     name=name@entry=0x7fff2548d140 "client.example.com", af=af@entry=2, 
>     result=result@entry=0x7fff2548d120, buffer=buffer@entry=0x1f33590 "\177", 
>     buflen=buflen@entry=992, errnop=errnop@entry=0x7fda3d8966a0, 
>     h_errnop=h_errnop@entry=0x7fff2548d10c, ttlp=ttlp@entry=0x0, canonp=canonp@entry=0x0)
>     at nss_dns/dns-host.c:192
> #7  0x00007fda2f277af0 in _nss_dns_gethostbyname_r (
>     name=0x7fff2548d140 "client.example.com", result=0x7fff2548d120, 
>     buffer=0x1f33590 "\177", buflen=992, errnop=0x7fda3d8966a0, h_errnop=0x7fff2548d10c)
>     at nss_dns/dns-host.c:273
> #8  0x00007fda39c9e163 in __gethostbyname_r (
>     name=name@entry=0x7fff2548d140 "client.example.com", 
>     resbuf=resbuf@entry=0x7fff2548d120, buffer=0x1f33590 "\177", buflen=buflen@entry=992, 
>     result=result@entry=0x7fff2548d118, h_errnop=h_errnop@entry=0x7fff2548d10c)
>     at ../nss/getXXbyYY_r.c:266
> #9  0x00007fda3bb1b3de in ldap_pvt_gethostbyname_a (
>     name=name@entry=0x7fff2548d140 "client.example.com", 
>     resbuf=resbuf@entry=0x7fff2548d120, buf=buf@entry=0x7fff2548d110, 
>     result=result@entry=0x7fff2548d118, herrno_ptr=herrno_ptr@entry=0x7fff2548d10c)
>     at util-int.c:350
> #10 0x00007fda3bb1b5d0 in ldap_pvt_get_fqdn (name=0x7fff2548d140 "client.example.com", 
>     name@entry=0x0) at util-int.c:748
> #11 0x00007fda3bb19b47 in ldap_int_initialize (
>     gopts=gopts@entry=0x7fda3bd40000 <ldap_int_global_options>, dbglvl=dbglvl@entry=0x0)
>     at init.c:645
> #12 0x00007fda3bb1a627 in ldap_set_option (ld=0x0, option=24582, invalue=0x7fff2548d2b0)
>     at options.c:446
> #13 0x00007fda30951cf6 in setup_tls_config (basic_opts=0x1f30450)
>     at src/providers/ldap/sdap.c:533
> #14 0x00007fda308214b3 in ldap_id_init_internal (bectx=0x1f12b40, ops=0x1f12cb0, 
>     pvt_data=0x7fff2548d5e8) at src/providers/ldap/ldap_init.c:146
> #15 0x00007fda30821ba0 in sssm_ldap_id_init (bectx=0x1f12b40, ops=0x1f12cb0, 
>     pvt_data=0x1f12cb8) at src/providers/ldap/ldap_init.c:199
> #16 0x000000000041b227 in load_backend_module (ctx=0x1f12b40, bet_type=BET_ID, 
>     bet_info=0x1f12ca8, default_mod_name=0x0) at src/providers/data_provider_be.c:2346
> #17 0x000000000041ce4c in be_process_init (mem_ctx=0x1f0ba80, 
>     be_domain=0x1f093f0 "localipaldap", ev=0x1f0a630, cdb=0x1f0bb90)
>     at src/providers/data_provider_be.c:2520
> #18 0x000000000041fde6 in main (argc=3, argv=0x7fff2548e008)
>     at src/providers/data_provider_be.c:2743
> 
>  735         /* LDAP_OPT_X_TLS_REQUIRE_CERT has to be set as a global option,
>  736          * because the SSL/TLS context is initialized from this value. */
>  737         ret = ldap_set_option(NULL, LDAP_OPT_X_TLS_REQUIRE_CERT,
>  738                               &ldap_opt_x_tls_require_cert);
>  739         if (ret != LDAP_OPT_SUCCESS) {
>  740             DEBUG(SSSDBG_CRIT_FAILURE,
>  741                   "ldap_set_option failed: %s\n",sss_ldap_err2string(ret));
>  742             return EIO;
>  743         }
> 
> Thanks,

Hi,

I already replied on the 18th, but I sent the mail to Jan only by
accident. I'm copying my previous reply below:

FWIW, the backtrace comes from the SSSD. Only frames #14 and up are
really relevant.

Since SSSD is often used in some kind of offline mode (either
completely offline or just not connected to the VPN), startup should
in my opinion be non-blocking.

Could there maybe be an option to pass in the hostname during
initialization instead of having openldap figure it out? I'm fine with
contributing a patch, if we agree on what the direction should be.