[Bug 1003296] Re: lightdm crashed with SIGSEGV in _pam_winbind_change_pwd() when password is expiring

[Luca Lorenzetto]

I wrote and tested a patch that fixes the bug. Reading the source code i
found that this:

 _pam_log(ctx, LOG_CRIT, "Received [%s] reply from application.\n",
resp->resp);

So i searched on the auth.log logfile for this log entry and found:

pam_winbind(lightdm:auth): Received [(null)] reply from application

Then i found on a the crashfile stackthread:

#0  __strcasecmp_l_ssse3 () at ../sysdeps/i386/i686/multiarch/strcmp-ssse3.S:293
 No locals.
 #1  0xb7221398 in _pam_winbind_change_pwd (ctx=<optimized out>) at ../nsswitch/pam_winbind.c:834
         msg = {msg_style = 5, msg = 0xb7228f90 "Do you want to change your password now?"}
         pmsg = 0xbfc39810
         resp = 0x85831a8
         prompt = <optimized out>
         ret = <optimized out>
         retval = false

So the problem is on the call of strcasecmp with null as first
parameter.

Attached the patch that fixes the issue.

I tested against the latest sources for precise that can be downloaded
with:

apt-get source samba


** Patch added: "Fixes bug adding a check for a null value before calling strcasecmp"
   https://bugs.launchpad.net/ubuntu/+source/samba/+bug/1003296/+attachment/3307085/+files/bug_lp_1003296.diff

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https://bugs.launchpad.net/bugs/1003296

Title:
  lightdm crashed with SIGSEGV in _pam_winbind_change_pwd() when
  password is expiring

Status in “samba” package in Ubuntu:
  Confirmed
Status in “samba” source package in Precise:
  Confirmed

Bug description:
  My precise client is member of a Windows Domain. A domain user can
  login using samba/winbind without problem in tty and via lightdm if
  the user password is ok.

  If the password is expiring a domain user logs in correctly via TTY,
  with a message "Your password is expiring in 10 days". if tries with
  lightdm the user gets the message "Your password is expiring in 10
  days", but then returns to the username request.

  On /var/log/syslog i get:

  May 23 08:50:52 tv52605 kernel: [ 1046.645230] lightdm[2415]: segfault
  at 0 ip b73d976a sp bfd66fa8 error 4 in libc-2.15.so[b729c000+19f000]

  for each time the user tries to login with the domain user
  credentials.

  Expected behaviour:

  the user sees the message  "Your password is expiring in 10 days",
  then logs in (like gdm in ubuntu 10.04 does).

  I attach the crash file i found in /var/crash/ (that i'm unable to
  send via apport-bug tue to same strange bug)

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