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Classics Forum

Re: ESQL/C Programs take very long time to start u

Posted By: Fernando Nunes
Date: Wednesday, 18 April 2018, at 12:33 p.m.

In Response To: Re: ESQL/C Programs take very long time to start u (RICHARD SPITZ)

On Wed, Apr 18, 2018 at 6:17 PM, RICHARD SPITZ <
richard.spitz@med.uni-muenchen.de> wrote:

> Fernando,
>
> thank you very much for your detailed response. I had written a comment in
> your blog article because that had been the most profound and helpful info
> I
> had found about configuring IDS with PAM support.
>
> > ESQL/C will most probably (that's what I'd like to test/debug) need
> > to get the user ID *before* trying to connect to IDS. And that's
> > where it's taking time.
>
> Exactly. I think I had written before in this thread that the delay occurs
> before the database connection is established. What's puzzling me is the
> way
> ESQL/C does this: First it goes through all the "pain" of reading
> /proc/self/loginuid and trying to verify that uid via the mechanisms
> defined
> in /etc/nsswitch.conf (which MUST fail in case of loginuid "-1", and
> causes
> the delay), and then it uses getuid() anyway to continue happily
> everafter.
>
> > That probably means that the LDAP integration software you're
> > using "hijacks" some internal functions/libraries...
>
> Well, I'm using a perfectly standard and well documented mechanism for
> that:
> sssd. This is nothing fancy and is integrated into current versions of
> GLIBC,
> that is also why PAM is not even needed to connect to IDS as an LDAP user.
>
> > When you say "interactive" may I assume you opened an SSH/telnet
> > to the server using the user name of the user? Or have you done an
> su/sudo?
>
> Interactive means that I am in a normal user shell (opened via SSH/PuTTY)
> on
> the Linux machine Hosting IDS and executing the shell script that is
> normally
> invoked by the SPL.
>
> > Assuming you did that directly the login process is going through
> > the authentication and creates the "session context" that makes the
> > calls run fast
>
> The login process sets /proc/self/loginuid for the shell, which is
> inherited
> by the program or shell script I'm starting.
>
> > This is not being set when a daemon (Informix) changes a process
> > identity which is what the SYSTEM SPL instruction triggers.
>
> Exactly. IDS (oninit) is the daemon, and the PAM module pam_loginuid.so is
> designed to set /proc/self/loginuid. That (pseudo) file is writable only
> for
> root, otherwise it would be trivial to write the correct uid to it but of
> course a huge security issue.
>
> > 1- Understand why the process takes time after trying to get that
> > info from the file. Is it calling a daemon for cache, talking to
> > the LDAP server, etc?. And how can that time be reduced?
>
> As written before, the problem is that ESQL/C is trying the UID of "-1"
> (read
> from /proc/self/loginuid) to query /etc/passwd and sssd, which MUST be
> unsuccessful. That UID can not be found in any local cache, that's why a
> query
> to the AD servers is done which is of course also unsuccessful. All of
> this
> takes time, a query with a correct UID takes only milliseconds.
>
> > 2- Check the use of the pam_loginuid in your system.
>
> That's what I've been doing all along. Is there a mechanism to make IDS
> (and
> other "daemons", like Apache) use that module when invoking subshells or
> processes?
>
> > I suppose the delay is also noticeable when you do the login.
>
> No, a valid user login works instantly, no noticeable delay.
>
> > 1- Can you change the ESQL/C to CONNECT with a specific user?
> > Maybe in that case it doesn't need to get the UID?
>
> Tried both implicit and explicit connections, no difference in behaviour.
>
> > 2- You probably can reproduce this by scheduling the process in the
> > crontab.
>
> crond is PAM-enabled and uses pam_loginuid.so, so /proc/self/loginuid is
> set
> to the correct UID. I already verified that by scheduling the ESQL/C
> program
> in cron.
>
> > 3- On many ocassions this weird delays are caused by issues in reverse
> > lookups (IP to names).
>
> No problem there, I can assure you.
>
> > I honestly don't know (strace should help) what ESQL/C calls when it
> > starts....
>
> I can send you a complete strace output, but I already mentioned the
> relevant
> parts in this thread.
>
> > I'm sure Jonathan Leffler would be able to provide some more
> > info on this, but I haven't seen him here for a while.
>
> Honestly, I had hoped that he might read this...
>
> > Note that in noway ESQL/C directly accesses the /proc/self/loginuid.
> > That's a consequence on a system call and your system configuration....
>
> Sorry, but I think you're wrong. The strace traces prove that the ESQL/C
> program itself reads /proc/self/loginuid, and that ONLY happens if the
> program
> establishes a database connection somewhere later in the program. I wrote
> a
> dummy ESQL/C program that doesn't open a database connection, and this
> dummy
> program doesn't read /proc/self/loginuid and does no user verification at
> all.
>
> Regards, Richard
>
>
No. I understand you got that from strace. And I didn't mean that the
ESQL/C process does not read the file.
What I mean is that ESQL/C only calls "standard" POSIX functions. And this
functions in your system (Linux + kernel version + configuration +
whatever) trigger those operations.
We would need to understand what call triggers that and if there's a way to
workaround it.
I thought, apprently wrongly, that it was the call to getuid which I
confirmed happens on an ESQL/C process. That's why I sent you a test case
with that call.
A possible way to try to find that would be to run the ESQL/C program in a
debugger and set a couple of breakpoints in OS functions close to the
sequence where it has delays.
When the program stops and returns control to the debugger try to run a
"where" and see what's in there. An example with getuid():

castelo@stardust.onlinedomus.net:informix-> gdb ./test.exe
GNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-100.el7_4.1
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html
>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /tmp/test.exe...(no debugging symbols found)...done.
(gdb) break getuid
Function "getuid" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (getuid) pending.
(gdb) run
Starting program: /tmp/./test.exe
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, 0x00007ffff640b080 in getuid () from /lib64/libc.so.6
Missing separate debuginfos, use: debuginfo-install
glibc-2.17-196.el7_4.2.x86_64 nss-softokn-freebl-3.28.3-8.el7_4.x86_64
(gdb) where
#0 0x00007ffff640b080 in getuid () from /lib64/libc.so.6
#1 0x00007ffff79597e7 in cmInit () from
/opt/informix/csdk410fc7w1/lib/libifasf.so
#2 0x00007ffff7950ddf in asfInit () from
/opt/informix/csdk410fc7w1/lib/libifasf.so
#3 0x00007ffff795196b in ASF_Call () from
/opt/informix/csdk410fc7w1/lib/libifasf.so
#4 0x00007ffff7b99a88 in asf_init () from
/opt/informix/csdk410fc7w1/lib/esql/libifsql.so
#5 0x00007ffff7b9ce0d in sqli_connect_open () from
/opt/informix/csdk410fc7w1/lib/esql/libifsql.so
#6 0x0000000000400916 in main ()
(gdb)

In this case the "CONNECT/DATABASE" statement triggers several calls in the
Informix LIBS and then we jump into the getuid().
You may need to go over several attempts if you can only set the breakpoint
to common functions like "open()"...

Once we find the POSIX function which is causing the sequence that causes
the delays we may have a shot of reconfigure something to solve it.
getuid() for example is necessary to get the user id under which we run....

Regards.

>
> *******************************************************************************
>
> Forum Note: Use "Reply" to post a response in the discussion forum.
>
>

--
Fernando Nunes
Portugal

http://informix-technology.blogspot.com
My email works... but I don't check it frequently...

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