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Classics Forum

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

Posted By: RICHARD SPITZ
Date: Wednesday, 18 April 2018, at 12:17 p.m.

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

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

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