[Bug 1397250] Re: SIGPIPE not caught in do_atfork_child()

[Jon Grimm]

OK, built trusty's libnss-ldap with the patch referenced by the bug
submitter.   Indeed, it too resolved the issue.

So to summarize:
1) Only trusty's libnss-ldap seems to fail. 
2) The bug seems fixable by any of the following:
  a) patch in comment #1, or
  b) updating trusty to xenial/yakkety libnss-ldap (with the caveat that I have no clue as to why this fixes it!)
  c) updating to upstream, which also has the patch referenced in comment #1. 


I'm leaning towards a because its intentionally the upstream fix for the bug, and even if I can't reproduce xenial/yakkety, it seems a safe enough fix (I will test this assumption) to apply there too.  I also think the amount of changes in b) & c) are too numerous to safely put back to trusty.

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https://bugs.launchpad.net/bugs/1397250

Title:
  SIGPIPE not caught in do_atfork_child()

Status in nss_ldap:
  Fix Released
Status in libnss-ldap package in Ubuntu:
  Triaged

Bug description:
  Ubuntu version: Ubuntu 14.04.1 LTS
  Package version: libnss-ldap_264-2.2ubuntu4

  If a process using libnss-ldap calls fork() and SIGPIPE was blocked, the atfork() handler in the child process failed to catch the SIGPIPE as it was supposed to do, that is in the call to  do_close_no_unbind().  So that, the uncaught SIGPIPE will be eventually
  delivered when the child unblocks signals. This usually make the child process die unexpectedly.

  I found a well-known Linux vendor fixed this issue with the following
  patch. This unblocks the SIGPIPE before calling do_close_no_unbind()
  and restores the original sigmask afterwards:

  diff -up nss_ldap/ldap-nss.c nss_ldap/ldap-nss.c
  --- nss_ldap/ldap-nss.c 2009-12-07 20:57:33.000000000 -0500
  +++ nss_ldap/ldap-nss.c 2009-12-07 20:58:56.000000000 -0500
  @@ -532,8 +532,13 @@
   static void
   do_atfork_child (void)
   {
  +  sigset_t unblock, mask;
     debug ("==> do_atfork_child");
  +  sigemptyset(&unblock);
  +  sigaddset(&unblock, SIGPIPE);
  +  sigprocmask(SIG_UNBLOCK, &unblock, &mask);
     do_close_no_unbind ();
  +  sigprocmask(SIG_SETMASK, &mask, NULL);
     _nss_ldap_leave ();
     debug ("<== do_atfork_child");
   }

  I'd like to see this patch applied.

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