suggested fix for the sigchld race

[Nicolas Williams]

Does this make it unnecessary to block SIGCHLD around where
child_terminated is manipulated? At first glance I'd say yes...

Your patch is rather elegant and simple.

The extra file descriptors needed should not be a problem, I don't
think. Why did you list that as a disadvantage?

Below is a patch to misc.h/misc.c/config.h.in to deal with signal
blocking. And sigprocmask and sigblock need to be added to the
configure.in list of function checks. And the code in serverloop2() that
manipulates child_terminated needs to be bracketed with calls to
block_sigchld()/unblock_sigchld(). I'm not recommending this patch, mind
you. I'll test yours...

Nico


On Wed, Oct 31, 2001 at 05:42:01PM +0100, Markus Friedl wrote:
> comments?
> 
> alternatives: sigsetjmp(ugly) and pselect(not portable, available)
> drawback: additional filedescriptors.
> 

Index: 2_9_p2_w_gss_krb5_named_keys.15/config.h.in
--- 2_9_p2_w_gss_krb5_named_keys.15/config.h.in Tue, 26 Jun 2001 16:27:13 -0400 (OpenSSH/f/45_config.h.i 1.3 644)
+++ 2_9_p2_w_gss_krb5_named_keys.16(w)/config.h.in Tue, 30 Oct 2001 15:55:15 -0500 (OpenSSH/f/45_config.h.i 1.4 644)
@@ -542,6 +542,12 @@
 /* Define if you have the sigvec function.  */
 #undef HAVE_SIGVEC
 
+/* Define if you have the sigprocmask function. */
+#undef HAVE_SIGPROCMASK
+
+/* Define if you have the sigblock function. */
+#undef HAVE_SIGBLOCK
+
 /* Define if you have the snprintf function.  */
 #undef HAVE_SNPRINTF
 
Index: 2_9_p2_w_gss_krb5_named_keys.15/misc.h
--- 2_9_p2_w_gss_krb5_named_keys.15/misc.h Thu, 03 May 2001 16:12:13 -0400 (OpenSSH/i/45_misc.h 1.1 644)
+++ 2_9_p2_w_gss_krb5_named_keys.16(w)/misc.h Tue, 30 Oct 2001 14:33:44 -0500 (OpenSSH/i/45_misc.h 1.2 644)
@@ -32,3 +32,6 @@
 /* wrapper for signal interface */
 typedef void (*mysig_t)(int);
 mysig_t mysignal(int sig, mysig_t act);
+
+void block_sigchld();
+void unblock_sigchld();
Index: 2_9_p2_w_gss_krb5_named_keys.15/misc.c
--- 2_9_p2_w_gss_krb5_named_keys.15/misc.c Fri, 22 Jun 2001 15:59:54 -0400 (OpenSSH/i/46_misc.c 1.2 644)
+++ 2_9_p2_w_gss_krb5_named_keys.16(w)/misc.c Tue, 30 Oct 2001 16:22:43 -0500 (OpenSSH/i/46_misc.c 1.3 644)
@@ -156,3 +156,34 @@
 	return (signal(sig, act));
 #endif
 }
+
+#ifdef HAVE_SIGPROCMASK
+static sigset_t osigset;
+#elif HAVE_SIGBLOCK
+static int osigmask;
+#endif
+
+void
+block_sigchld()
+{
+#ifdef HAVE_SIGPROCMASK
+        sigset_t sigchld_set;
+	(void) sigemptyset(&sigchld_set);
+	(void) sigaddset(&sigchld_set, SIGCHLD);
+	if (sigprocmask(SIG_BLOCK, &sigchld_set, &osigset) < 0)
+		debug("block_sigchld: sigprocmask() returned error %s", strerror(errno));
+#elif HAVE_SIGBLOCK
+	osigmask = sigblock(sigmask(SIGCHLD));
+#endif
+}
+
+void
+unblock_sigchld()
+{
+#ifdef HAVE_SIGPROCMASK
+	if (sigprocmask(SIG_UNBLOCK, &osigset, NULL) < 0)
+		debug("block_sigchld: sigprocmask() returned error %s", strerror(errno));
+#elif HAVE_SIGBLOCK
+	(void) sigsetmask(osigmask);
+#endif
+}

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