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Re: NIS+ groups, segfaults


From: Dirk Wetter
Subject: Re: NIS+ groups, segfaults
Date: Thu, 1 Mar 2001 12:14:59 -0500 (EST)

Thorsten,

thx for the answer, hope you had a nice vacation :-).

in the meantime we think we tracked down the culprit,
it's in our case "_nss_compat_initgroups" in
"./glibc-2.1/nis/nss_compat/compat-initgroups.c".
just increasing the buflen before the first time calling
the "while" loop helps. the whole is more a workaround
of course. the real culprit is probably __alloca.
internal_getgrent_r returns with NSS_STATUS_TRYAGAIN
for the first one since of our big NIS+ groups don't fit
into 1024 bytes, the second time __alloca
is being called it corrupts the stack somehow. the segfault
is way later, when another function exits.

as a quick and better workaround we thought we could increase
NSS_BUFLEN_PASSWD which 1024 (the value actually returned
by sysconf (_SC_GETPW_R_SIZE_MAX)... howto do that? looks
like it is not a parameter which is tunable during runtime?


        ~dirkw


PS: that piece of code seems to be the same for glibc 2.2.2


On Thu, 1 Mar 2001, Thorsten Kukuk wrote:

> On Wed, Feb 28, Dirk Wetter wrote:
>
> >
> > Hi all,
> >
> > below you find a mail posted in November 2000 to the NIS+
> > Linux mailing list. Looks also for us like there's a
> > problem, which hasn't been fixed. I know that we are
> > using not the very recent libc, but I like to find out where
> > the problem is anyhow.
> >
> > We are using a plain SuSE 7.0 with a libc-2.1.3.
> > We have 2 groups with more than 700 chars, as soon as
> > we enable the compat or nisplus mode  in /etc/nsswitch.conf for
> > groups we get segfaults while authenticating. also the strace
> > output makes us assuming  that  there is a bug. No problem if
> > we dump the NIS+ groups and append it to /etc/group.
> >
> > So, how can we find the bug and to fix it in libc 2.1.3 ??
>
> The last time I had access to a NIS+ server I couldn't reproduce
> any problems with NIS+ groups. But it looks like there is one
> problem with netgroups and static linking and one with the
> initgroups function. Nobody was yet able to track them down.
>
>   Thorsten
>
> --
> Thorsten Kukuk       http://www.suse.de/~kukuk/       address@hidden
> SuSE GmbH            Schanzaeckerstr. 10            90443 Nuernberg
> Linux is like a Vorlon.  It is incredibly powerful, gives terse,
> cryptic answers and has a lot of things going on in the background.
>





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