[Bug 1397250] [NEW] SIGPIPE not caught in do_atfork_child()

[Marcello Blancasio]

Public bug reported:

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.

** Affects: libnss-ldap (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: atfork fork sigpipe

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

Title:
  SIGPIPE not caught in do_atfork_child()

Status in libnss-ldap package in Ubuntu:
  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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