- Unblock and catch SIGCHLD from spawned shell commands
--- tcp_wrappers_7.6/shell_cmd.c.sigchld	1994-12-28 17:42:44.000000000 +0100
+++ tcp_wrappers_7.6/shell_cmd.c	2007-06-28 15:42:17.000000000 +0200
@@ -20,6 +20,11 @@
 #include <stdio.h>
 #include <syslog.h>
 #include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <sys/wait.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 
 extern void exit();
 
@@ -31,13 +36,42 @@
 
 static void do_child();
 
+/*
+ * The sigchld handler. If there is a SIGCHLD caused by a child other than
+ * ours, we set a flag and raise the signal later.
+ */
+volatile static int foreign_sigchld;
+volatile static int our_child_pid;
+static void sigchld(int sig, siginfo_t *si, void *unused)
+{
+    if (si && si->si_pid != our_child_pid)
+	foreign_sigchld = 1;
+}
+
 /* shell_cmd - execute shell command */
 
 void    shell_cmd(command)
 char   *command;
 {
     int     child_pid;
-    int     wait_pid;
+
+    struct sigaction new_action, old_action;
+    sigset_t new_mask, old_mask, empty_mask;
+
+    new_action.sa_sigaction = &sigchld;
+    new_action.sa_flags = SA_SIGINFO;
+    sigemptyset(&new_action.sa_mask);
+    sigemptyset(&new_mask);
+    sigemptyset(&empty_mask);
+    sigaddset(&new_mask, SIGCHLD);
+
+    /*
+     * Set the variables for handler, set the handler and block the signal
+     * until we have the pid.
+     */
+    foreign_sigchld = 0; our_child_pid = 0;
+    sigprocmask(SIG_BLOCK, &new_mask, &old_mask);
+    sigaction(SIGCHLD, &new_action, &old_action);
 
     /*
      * Most of the work is done within the child process, to minimize the
@@ -49,12 +83,26 @@
 	tcpd_warn("cannot fork: %m");
 	break;
     case 00:					/* child */
+	/* Clear the blocked mask for the child not to be surprised. */
+	sigprocmask(SIG_SETMASK, &empty_mask, 0);
 	do_child(command);
 	/* NOTREACHED */
     default:					/* parent */
-	while ((wait_pid = wait((int *) 0)) != -1 && wait_pid != child_pid)
-	     /* void */ ;
+	our_child_pid = child_pid;
+	sigprocmask(SIG_UNBLOCK, &new_mask, 0);
+	while (waitpid(child_pid, (int *) 0, 0) == -1 && errno == EINTR);
     }
+
+    /*
+     * Revert the signal mask and the SIGCHLD handler.
+     */
+    sigprocmask(SIG_SETMASK, &old_mask, 0);
+    sigaction(SIGCHLD, &old_action, 0);
+
+    /* If there was a foreign SIGCHLD, raise it after we have restored the old
+     * mask and handler. */
+    if (foreign_sigchld)
+	raise(SIGCHLD);
 }
 
 /* do_child - exec command with { stdin, stdout, stderr } to /dev/null */