[Bug 958305] Re: nscd crashed with SIGSEGV in _nss_files_init()

[Daniel J Blueman]

Rebuilding unscd from source and running an unstripped binary, we see it
crashing in libc's nsswitch.c:875.

#if __OPTION_EGLIBC_INET
/* Called by nscd and nscd alone.  */
void
__nss_disable_nscd (void (*cb) (size_t, struct traced_file *))
{
# ifdef PTR_MANGLE
  PTR_MANGLE (cb);   <---- NULL ptr deref
# endif
  nscd_init_cb = cb;
  is_nscd = true;

The 'cb' init callback function pointer is apparently optional; the
definition of PTR_DEMANGLE in sysdep.h doesn't say so.

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https://bugs.launchpad.net/bugs/958305

Title:
  nscd crashed with SIGSEGV in _nss_files_init()

Status in “eglibc” package in Ubuntu:
  New
Status in “unscd” package in Ubuntu:
  Confirmed

Bug description:
  Clean x86-64 install of precise as of 2012-03-17; unscd is hit with
  SEGV whenever it starts, ie 100% reproducability.

  ProblemType: Crash
  DistroRelease: Ubuntu 12.04
  Package: unscd 0.47-2build2
  ProcVersionSignature: Ubuntu 3.2.0-19.30-generic 3.2.11
  Uname: Linux 3.2.0-19-generic x86_64
  ApportVersion: 1.94.1-0ubuntu2
  Architecture: amd64
  Date: Sun Mar 18 11:18:59 2012
  Disassembly: => 0x1:	Cannot access memory at address 0x1
  ExecutablePath: /usr/sbin/nscd
  InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha amd64 (20120316)
  ProcCmdline: /usr/sbin/nscd
  ProcEnviron:
   LANGUAGE=en_SG:en
   TERM=linux
   LANG=en_SG.UTF-8
   SHELL=/bin/bash
  SegvAnalysis:
   Segfault happened at: 0x1:	Cannot access memory at address 0x1
   PC (0x00000001) not located in a known VMA region (needed executable region)!
  SegvReason: executing NULL VMA
  Signal: 11
  SourcePackage: unscd
  StacktraceTop:
   ?? ()
   _nss_files_init (cb=0x1) at nss_files/files-init.c:47
   nss_load_library (ni=<optimized out>) at nsswitch.c:412
   nss_load_all_libraries (def=0x7f03dd560b74 "dns [!UNAVAIL=return] files", service=0x7f03dd560b90 "hosts") at nsswitch.c:875
   __nss_disable_nscd (cb=<optimized out>) at nsswitch.c:895
  Title: nscd crashed with SIGSEGV in _nss_files_init()
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups:

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