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

[Jon Grimm]

Consulted with racb, my plan of attack will be to SRU the patch only
into trusty (with push to zesty first) for now. If someone else can
reproduce the bug on xenial and/or yakkety, AND is will to test fix,
I'll SRU into those releases correspondingly.

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Title:
  SIGPIPE not caught in do_atfork_child()

Status in nss_ldap:
  Fix Released
Status in libnss-ldap package in Ubuntu:
  Triaged
Status in libnss-ldap source package in Trusty:
  New
Status in libnss-ldap source package in Xenial:
  New
Status in libnss-ldap source package in Yakkety:
  New

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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