Patch: Implement surrogate parent for back-shell (ITS#1815)

================ Written by Hallvard B. Furuseth and placed into the public domain. This software is not subject to any license of the University of Oslo. ================ A surrogate parent is supposed to keep back-shell children from deadlocking due to resources locked by a threading parent. Implementation note: The surrogate parent closes all unused file descriptors, so it logs errors to stderr instead of via Debug() and uses relloc() instead of ch_realloc(). Also close a file descriptor leak if fork() fails in fork.c. Hallvard B. Furuseth <h.b.furuseth@usit.uio.no>, May 2002.
2025-01-12 10:54:48 +08:00 · 2002-05-15 06:18:14 +00:00 · 2002-05-15 06:18:14 +00:00 · 4e51bba217
commit 4e51bba217
parent d8388e461d
17 changed files with 417 additions and 62 deletions
--- a/29
+++ b/29
@ -1,6 +1,6 @@
 #! /bin/sh
 # $OpenLDAP$
-# from OpenLDAP: pkg/ldap/configure.in,v 1.417 2002/05/13 16:48:37 kurt Exp  
+# from OpenLDAP: pkg/ldap/configure.in,v 1.418 2002/05/13 18:16:47 kurt Exp  

 # Copyright 1998-2002 The OpenLDAP Foundation.  All Rights Reserved.
 # 
@ -19622,7 +19622,7 @@ else
 #if SASL_VERSION_MAJOR == 1  && SASL_VERSION_MINOR >= 5
 	char *__sasl_compat = "1.5.x okay";
 #elif SASL_VERSION_MAJOR == 2  && SASL_VERSION_MINOR > 1
-	__sasl_compat "2.2+ or better okay";
+	__sasl_compat "2.2+ or better okay (we guess)";
 #elif SASL_VERSION_MAJOR == 2  && SASL_VERSION_MINOR == 1 \
 	&& SASL_VERSION_STEP >=3
 	__sasl_compat = "2.1.3+ or better okay";
@ -21790,6 +21790,7 @@ for ac_func in \
 	read			\
 	recv			\
 	recvfrom		\
+	recvmsg			\
 	setpwfile		\
 	setgid			\
 	setegid			\
@ -21818,12 +21819,12 @@ for ac_func in \

 do
 echo $ac_n "checking for $ac_func""... $ac_c" 1>&6
-echo "configure:21822: checking for $ac_func" >&5
+echo "configure:21823: checking for $ac_func" >&5
 if eval "test \"\${ac_cv_func_$ac_func+set}\" = set"; then
  echo $ac_n "(cached) $ac_c" 1>&6
 else
  cat > conftest.$ac_ext <<EOF
-#line 21827 "configure"
+#line 21828 "configure"
 #include "confdefs.h"
 /* System header to define __stub macros and hopefully few prototypes,
    which can conflict with char $ac_func(); below.  */
@ -21847,7 +21848,7 @@ f = $ac_func;

 ; return 0; }
 EOF
-if { (eval echo configure:21851: \"$ac_link\") 1>&5; (eval $ac_link) 2>&5; } && test -s conftest${ac_exeext}; then
+if { (eval echo configure:21852: \"$ac_link\") 1>&5; (eval $ac_link) 2>&5; } && test -s conftest${ac_exeext}; then
  rm -rf conftest*
  eval "ac_cv_func_$ac_func=yes"
 else
@ -21875,12 +21876,12 @@ done
 for ac_func in getopt
 do
 echo $ac_n "checking for $ac_func""... $ac_c" 1>&6
-echo "configure:21879: checking for $ac_func" >&5
+echo "configure:21880: checking for $ac_func" >&5
 if eval "test \"\${ac_cv_func_$ac_func+set}\" = set"; then
  echo $ac_n "(cached) $ac_c" 1>&6
 else
  cat > conftest.$ac_ext <<EOF
-#line 21884 "configure"
+#line 21885 "configure"
 #include "confdefs.h"
 /* System header to define __stub macros and hopefully few prototypes,
    which can conflict with char $ac_func(); below.  */
@ -21904,7 +21905,7 @@ f = $ac_func;

 ; return 0; }
 EOF
-if { (eval echo configure:21908: \"$ac_link\") 1>&5; (eval $ac_link) 2>&5; } && test -s conftest${ac_exeext}; then
+if { (eval echo configure:21909: \"$ac_link\") 1>&5; (eval $ac_link) 2>&5; } && test -s conftest${ac_exeext}; then
  rm -rf conftest*
  eval "ac_cv_func_$ac_func=yes"
 else
@ -21937,13 +21938,13 @@ fi

 # Check Configuration
 echo $ac_n "checking declaration of sys_errlist""... $ac_c" 1>&6
-echo "configure:21941: checking declaration of sys_errlist" >&5
+echo "configure:21942: checking declaration of sys_errlist" >&5
 if eval "test \"\${ol_cv_dcl_sys_errlist+set}\" = set"; then
  echo $ac_n "(cached) $ac_c" 1>&6
 else
  
 	cat > conftest.$ac_ext <<EOF
-#line 21947 "configure"
+#line 21948 "configure"
 #include "confdefs.h"

 #include <stdio.h>
@ -21956,7 +21957,7 @@ int main() {
 char *c = (char *) *sys_errlist
 ; return 0; }
 EOF
-if { (eval echo configure:21960: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
+if { (eval echo configure:21961: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
  rm -rf conftest*
  ol_cv_dcl_sys_errlist=yes
 	ol_cv_have_sys_errlist=yes
@ -21979,20 +21980,20 @@ EOF


 	echo $ac_n "checking existence of sys_errlist""... $ac_c" 1>&6
-echo "configure:21983: checking existence of sys_errlist" >&5
+echo "configure:21984: checking existence of sys_errlist" >&5
 if eval "test \"\${ol_cv_have_sys_errlist+set}\" = set"; then
  echo $ac_n "(cached) $ac_c" 1>&6
 else
  
 		cat > conftest.$ac_ext <<EOF
-#line 21989 "configure"
+#line 21990 "configure"
 #include "confdefs.h"
 #include <errno.h>
 int main() {
 char *c = (char *) *sys_errlist
 ; return 0; }
 EOF
-if { (eval echo configure:21996: \"$ac_link\") 1>&5; (eval $ac_link) 2>&5; } && test -s conftest${ac_exeext}; then
+if { (eval echo configure:21997: \"$ac_link\") 1>&5; (eval $ac_link) 2>&5; } && test -s conftest${ac_exeext}; then
  rm -rf conftest*
  ol_cv_have_sys_errlist=yes
 else
--- a/configure.in
+++ b/configure.in
@ -2426,6 +2426,7 @@ AC_CHECK_FUNCS(		\
 	read			\
 	recv			\
 	recvfrom		\
+	recvmsg			\
 	setpwfile		\
 	setgid			\
 	setegid			\
--- a/include/portable.h.in
+++ b/include/portable.h.in
@ -224,6 +224,9 @@
 /* Define if you have the recvfrom function.  */
 #undef HAVE_RECVFROM

+/* Define if you have the recvmsg function.  */
+#undef HAVE_RECVMSG
+
 /* Define if you have the sched_yield function.  */
 #undef HAVE_SCHED_YIELD

--- a/include/portable.nt
+++ b/include/portable.nt
@ -243,6 +243,9 @@
 /* Define if you have the recvfrom function.  */
 /* #undef HAVE_RECVFROM */

+/* Define if you have the recvmsg function.  */
+/* #undef HAVE_RECVMSG */
+
 /* Define if you have the sched_yield function.  */
 /* #undef HAVE_SCHED_YIELD */

--- a/servers/slapd/back-shell/abandon.c
+++ b/servers/slapd/back-shell/abandon.c
@ -29,7 +29,7 @@ shell_back_abandon(
 	Operation		*o;

 	/* no abandon command defined - just kill the process handling it */
-	if ( si->si_abandon == NULL ) {
+	if ( IS_NULLCMD( si->si_abandon ) ) {
 		ldap_pvt_thread_mutex_lock( &conn->c_mutex );
 		pid = -1;
 		LDAP_STAILQ_FOREACH( o, &conn->c_ops, o_next ) {
--- a/servers/slapd/back-shell/add.c
+++ b/servers/slapd/back-shell/add.c
@ -27,7 +27,7 @@ shell_back_add(
 	FILE			*rfp, *wfp;
 	int			len;

-	if ( si->si_add == NULL ) {
+	if ( IS_NULLCMD( si->si_add ) ) {
 		send_ldap_result( conn, op, LDAP_UNWILLING_TO_PERFORM, NULL,
 		    "add not implemented", NULL, NULL );
 		return( -1 );
--- a/servers/slapd/back-shell/bind.c
+++ b/servers/slapd/back-shell/bind.c
@ -31,7 +31,7 @@ shell_back_bind(
 	FILE			*rfp, *wfp;
 	int			rc;

-	if ( si->si_bind == NULL ) {
+	if ( IS_NULLCMD( si->si_bind ) ) {
 		send_ldap_result( conn, op, LDAP_UNWILLING_TO_PERFORM, NULL,
 		    "bind not implemented", NULL, NULL );
 		return( -1 );
--- a/servers/slapd/back-shell/compare.c
+++ b/servers/slapd/back-shell/compare.c
@ -28,7 +28,7 @@ shell_back_compare(
 	struct shellinfo	*si = (struct shellinfo *) be->be_private;
 	FILE			*rfp, *wfp;

-	if ( si->si_compare == NULL ) {
+	if ( IS_NULLCMD( si->si_compare ) ) {
 		send_ldap_result( conn, op, LDAP_UNWILLING_TO_PERFORM, NULL,
 		    "compare not implemented", NULL, NULL );
 		return( -1 );
--- a/servers/slapd/back-shell/config.c
+++ b/servers/slapd/back-shell/config.c
@ -15,6 +15,28 @@
 #include "slap.h"
 #include "shell.h"

+#ifdef SHELL_SURROGATE_PARENT
+
+static struct berval make_cmd_info(
+	char **args
+)
+{
+	struct berval ret = { 0, 0 };
+	int i;
+	ber_len_t offset;
+	for( i = 0; args[i] != NULL; i++ )
+		ret.bv_len += strlen( args[i] ) + 1;
+	ret.bv_val = ch_malloc( ret.bv_len );
+	offset = 0;
+	for( i = 0; args[i] != NULL; i++ ) {
+		strcpy( ret.bv_val + offset, args[i] );
+		offset += strlen( args[i] ) + 1;
+	}
+	return ret;
+}
+
+#endif /* SHELL_SURROGATE_PARENT */
+
 int
 shell_back_db_config(
    BackendDB	*be,
@ -40,7 +62,7 @@ shell_back_db_config(
 			    fname, lineno );
 			return( 1 );
 		}
-		si->si_bind = charray_dup( &argv[1] );
+		si->si_bind = MAKE_CMD_INFO( &argv[1] );

 	/* command + args to exec for unbinds */
 	} else if ( strcasecmp( argv[0], "unbind" ) == 0 ) {
@ -50,7 +72,7 @@ shell_back_db_config(
 			    fname, lineno );
 			return( 1 );
 		}
-		si->si_unbind = charray_dup( &argv[1] );
+		si->si_unbind = MAKE_CMD_INFO( &argv[1] );

 	/* command + args to exec for searches */
 	} else if ( strcasecmp( argv[0], "search" ) == 0 ) {
@ -60,7 +82,7 @@ shell_back_db_config(
 			    fname, lineno );
 			return( 1 );
 		}
-		si->si_search = charray_dup( &argv[1] );
+		si->si_search = MAKE_CMD_INFO( &argv[1] );

 	/* command + args to exec for compares */
 	} else if ( strcasecmp( argv[0], "compare" ) == 0 ) {
@ -70,7 +92,7 @@ shell_back_db_config(
 			    fname, lineno );
 			return( 1 );
 		}
-		si->si_compare = charray_dup( &argv[1] );
+		si->si_compare = MAKE_CMD_INFO( &argv[1] );

 	/* command + args to exec for modifies */
 	} else if ( strcasecmp( argv[0], "modify" ) == 0 ) {
@ -80,7 +102,7 @@ shell_back_db_config(
 			    fname, lineno );
 			return( 1 );
 		}
-		si->si_modify = charray_dup( &argv[1] );
+		si->si_modify = MAKE_CMD_INFO( &argv[1] );

 	/* command + args to exec for modrdn */
 	} else if ( strcasecmp( argv[0], "modrdn" ) == 0 ) {
@ -90,7 +112,7 @@ shell_back_db_config(
 			    fname, lineno );
 			return( 1 );
 		}
-		si->si_modrdn = charray_dup( &argv[1] );
+		si->si_modrdn = MAKE_CMD_INFO( &argv[1] );

 	/* command + args to exec for add */
 	} else if ( strcasecmp( argv[0], "add" ) == 0 ) {
@ -100,7 +122,7 @@ shell_back_db_config(
 			    fname, lineno );
 			return( 1 );
 		}
-		si->si_add = charray_dup( &argv[1] );
+		si->si_add = MAKE_CMD_INFO( &argv[1] );

 	/* command + args to exec for delete */
 	} else if ( strcasecmp( argv[0], "delete" ) == 0 ) {
@ -110,7 +132,7 @@ shell_back_db_config(
 			    fname, lineno );
 			return( 1 );
 		}
-		si->si_delete = charray_dup( &argv[1] );
+		si->si_delete = MAKE_CMD_INFO( &argv[1] );

 	/* command + args to exec for abandon */
 	} else if ( strcasecmp( argv[0], "abandon" ) == 0 ) {
@ -120,7 +142,7 @@ shell_back_db_config(
 			    fname, lineno );
 			return( 1 );
 		}
-		si->si_abandon = charray_dup( &argv[1] );
+		si->si_abandon = MAKE_CMD_INFO( &argv[1] );

 	/* anything else */
 	} else {
--- a/servers/slapd/back-shell/delete.c
+++ b/servers/slapd/back-shell/delete.c
@ -27,7 +27,7 @@ shell_back_delete(
 	struct shellinfo	*si = (struct shellinfo *) be->be_private;
 	FILE			*rfp, *wfp;

-	if ( si->si_delete == NULL ) {
+	if ( IS_NULLCMD( si->si_delete ) ) {
 		send_ldap_result( conn, op, LDAP_UNWILLING_TO_PERFORM, NULL,
 		    "delete not implemented", NULL, NULL );
 		return( -1 );
--- a/servers/slapd/back-shell/fork.c
+++ b/servers/slapd/back-shell/fork.c
@ -9,6 +9,7 @@

 #include <stdio.h>

+#include <ac/errno.h>
 #include <ac/string.h>
 #include <ac/socket.h>
 #include <ac/unistd.h>
@ -16,18 +17,226 @@
 #include "slap.h"
 #include "shell.h"

+#ifdef SHELL_SURROGATE_PARENT
+
+#include <sys/uio.h>
+
+/* Use several socketpairs to the surrogate parent, because   *
+ * a single communication channel to it could be a bottleneck */
+ldap_pvt_thread_mutex_t shell_surrogate_fd_mutex[2];
+int                     shell_surrogate_fd[2] = { -1, -1 };
+/* Index to shell_surrogate_fd, and its mutex */
+ldap_pvt_thread_mutex_t shell_surrogate_index_mutex;
+static int              shell_surrogate_index = 1;
+
+pid_t                   shell_surrogate_pid = -1;
+
+#define  nread( fd, buf, len ) n_rw( 0, fd, buf, len )
+#define nwrite( fd, buf, len ) n_rw( 1, fd, buf, len )
+
+static int
+n_rw(
+	int do_write,
+	int fd,
+	void *buf,
+	int len
+)
+{
+	int ret = 0, i;
+	while( len ) {
+		for(;;) {
+			i = (do_write
+			     ? write( fd, buf, len )
+			     :  read( fd, buf, len ));
+			if( i < 0 ) {
+				if( errno == EINTR )
+					continue;
+				if( ret == 0 )
+					ret = -1;
+			}
+			break;
+		}
+		if( i <= 0 )
+			break;
+		ret += i;
+		buf = (char *)buf + i;
+		len -= i;
+	}
+	return ret;
+}
+
+void
+make_surrogate_parent( void )
+{
+	int pair[2][2], io[2], i, j, p, argc;
+	ber_len_t len, buflen, offset;
+	char *buf, **argv;
+	pid_t pid;
+
+	if( socketpair( AF_LOCAL, SOCK_STREAM, 0, pair[0] ) < 0 ||
+	    socketpair( AF_LOCAL, SOCK_STREAM, 0, pair[1] ) < 0   ) {
+		Debug( LDAP_DEBUG_ANY, "socketpair failed\n", 0, 0, 0 );
+		exit( EXIT_FAILURE );
+	}
+	fflush( NULL );
+	switch( fork() ) {
+	case -1:
+		Debug( LDAP_DEBUG_ANY, "fork failed\n", 0, 0, 0 );
+		exit( EXIT_FAILURE );
+	case 0:
+		break;
+	default:
+		shell_surrogate_fd[0] = pair[0][0];
+		shell_surrogate_fd[1] = pair[1][0];
+		close( pair[0][1] );
+		close( pair[1][1] );
+		return;
+	}
+
+	/* Close unused file descriptors */
+	for( i = 3, j = 32; j && i < 1024; i++ )
+		if( i != pair[0][1] && i != pair[1][1] && close( i ) < 0 )
+			--j;
+		else if( j < 32 )
+			j = 32;
+
+	/* Surrogate parent running */
+
+	buflen = 0;
+	buf = NULL;
+	argc = 0;
+	argv = NULL;
+	p = 0;
+
+	for(;;) {
+		/* Read file descriptors io[] from socket */ 
+		static char dummy;
+		static struct iovec iov = { &dummy, 1 };
+		struct msghdr msg;
+# ifdef CMSG_SPACE
+		union {
+			struct cmsghdr cm;
+			char control[CMSG_SPACE(sizeof(io))];
+		} control_un;
+		struct cmsghdr *cmptr;
+		msg.msg_control = control_un.control;
+		msg.msg_controllen = sizeof(control_un.control);
+# else
+		msg.msg_accrights = (caddr_t) io;
+		msg.msg_accrightslen = sizeof(io);
+# endif
+		msg.msg_name = NULL;
+		msg.msg_namelen = 0;
+		msg.msg_iov = &iov;
+		msg.msg_iovlen = 1;
+		msg.msg_flags = 0;
+		switch( recvmsg( pair[p][1], &msg, MSG_WAITALL ) ) {
+		case -1:
+			if( errno == EINTR )
+				continue;
+			_exit( EXIT_FAILURE );
+		case 0:
+			_exit( EXIT_SUCCESS );
+		}
+# ifdef CMSG_SPACE
+		if( (cmptr = CMSG_FIRSTHDR(&msg)) == NULL   ||
+		    cmptr->cmsg_len != CMSG_LEN(sizeof(io)) ||
+		    cmptr->cmsg_level != SOL_SOCKET         ||
+		    cmptr->cmsg_type != SCM_RIGHTS            ) {
+			fputs( "bad descriptor message received\n", stderr );
+			exit( EXIT_FAILURE );
+		}
+		memcpy( io, CMSG_DATA( cmptr ), sizeof(io) );
+# else
+		if( msg.msg_accrightslen != sizeof(io) ) {
+			fputs( "bad descriptor message received\n", stderr );
+			exit( EXIT_FAILURE );
+		}
+# endif
+
+		/* Read length of arguments and then arguments from socket */
+		if( nread( pair[p][1], &len, sizeof(len) ) != sizeof(len) ) {
+			fputs( "bad descriptor message received\n", stderr );
+			exit( EXIT_FAILURE );
+		}
+		if( buflen < len ) {
+			buf = realloc( buf, buflen = len );
+			if( buf == NULL ) {
+				fputs( "realloc failed\n", stderr );
+				exit( EXIT_FAILURE );
+			}
+		}
+		if( nread( pair[p][1], buf, len ) != len ) {
+			fputs( "bad descriptor message received\n", stderr );
+			exit( EXIT_FAILURE );
+		}
+		i = 0;
+		offset = 0;
+		while( offset < len ) {
+			if( i >= argc-1 ) {
+				argc += i + 10;
+				argv = realloc( argv, argc * sizeof(*argv) );
+				if( argv == NULL ) {
+					fputs( "realloc failed\n", stderr );
+					exit( EXIT_FAILURE );
+				}
+			}
+			argv[i++] = buf + offset;
+			offset += strlen( buf + offset ) + 1;
+		}
+		argv[i] = NULL;
+
+		/* Run program */
+		pid = fork();
+		switch( pid )
+		{
+		case 0:		/* child */
+			if( dup2( io[0], 0 ) == -1 || dup2( io[1], 1 ) == -1 ) {
+				fputs( "dup2 failed\n", stderr );
+				exit( EXIT_FAILURE );
+			}
+			close( io[0] );
+			close( io[1] );
+			close( pair[0][1] );
+			close( pair[1][1] );
+			execv( argv[0], argv );
+
+			fputs( "execv failed\n", stderr );
+			exit( EXIT_FAILURE );
+
+		case -1:	/* trouble */
+			fputs( "fork failed\n", stderr );
+			break;
+
+		default:	/* parent */
+			close( io[0] );
+			close( io[1] );
+			break;
+		}
+		if( nwrite( pair[p][1], &pid,
+		            sizeof(pid_t) ) != sizeof(pid_t) )  {
+			fputs( "could not send pid\n", stderr );
+			exit( EXIT_FAILURE );
+		}
+		p ^= 1;
+	}
+}
+#endif /* SHELL_SURROGATE_PARENT */
+
 pid_t
 forkandexec(
-    char	**args,
+    Cmd_info  args,
    FILE	**rfp,
    FILE	**wfp
 )
 {
-	int	p2c[2], c2p[2];
+	int	p2c[2] = { -1, -1 }, c2p[2];
 	pid_t	pid;

 	if ( pipe( p2c ) != 0 || pipe( c2p ) != 0 ) {
 		Debug( LDAP_DEBUG_ANY, "pipe failed\n", 0, 0, 0 );
+		close( p2c[0] );
+		close( p2c[1] );
 		return( -1 );
 	}

@ -37,27 +246,89 @@ forkandexec(
 	 *	parent *rfp <- c2p[0] | c2p[1] <- stdout child
 	 */

-#ifdef HAVE_THR
-	switch ( (pid = fork1()) )
-#else
-	switch ( (pid = fork()) )
-#endif
+#ifdef SHELL_SURROGATE_PARENT
+
 	{
-	case 0:		/* child */
+		int io[2] = { p2c[0], c2p[1] }, i, c;
+		static char dummy = '\0';
+		static struct iovec iov = { &dummy, 1 };
+		struct msghdr msg;
+# ifdef CMSG_SPACE
+		union {
+			struct cmsghdr cm;
+			char control[CMSG_SPACE(sizeof(io))];
+		} control_un;
+		struct cmsghdr *cmptr;
+		msg.msg_control = control_un.control;
+		msg.msg_controllen = sizeof(control_un.control);
+		cmptr = CMSG_FIRSTHDR(&msg);
+		cmptr->cmsg_len = CMSG_LEN(sizeof(io));
+		cmptr->cmsg_level = SOL_SOCKET;
+		cmptr->cmsg_type = SCM_RIGHTS;
+		memcpy( CMSG_DATA(cmptr), io, sizeof(io) );
+# else
+		msg.msg_accrights = (caddr_t) io;
+		msg.msg_accrightslen = sizeof(io);
+# endif
+		msg.msg_name = NULL;
+		msg.msg_namelen = 0;
+		msg.msg_iov = &iov;
+		msg.msg_iovlen = 1;
+		msg.msg_flags = 0;
+		ldap_pvt_thread_mutex_lock( &shell_surrogate_index_mutex );
+		i = shell_surrogate_index ^= 1;
+		ldap_pvt_thread_mutex_unlock( &shell_surrogate_index_mutex );
+		ldap_pvt_thread_mutex_lock( &shell_surrogate_fd_mutex[i] );
+		c = (sendmsg( shell_surrogate_fd[i], &msg, 0 ) == 1 &&
+			 nwrite( shell_surrogate_fd[i], &args.bv_len,
+			         sizeof(args.bv_len) ) == sizeof(args.bv_len) &&
+			 nwrite( shell_surrogate_fd[i], args.bv_val,
+			         args.bv_len ) == args.bv_len &&
+			 nread( shell_surrogate_fd[i], &pid,
+			        sizeof(pid) ) == sizeof(pid));
+		ldap_pvt_thread_mutex_unlock( &shell_surrogate_fd_mutex[i] );
+		close( p2c[0] );
+		close( c2p[1] );
+		if ( !c ) {
+			Debug( LDAP_DEBUG_ANY, "process creation failed\n", 0, 0, 0 );
+			close( p2c[1] );
+			close( c2p[0] );
+			close( shell_surrogate_fd[0] );
+			close( shell_surrogate_fd[1] );
+			shell_surrogate_fd[0] =
+				shell_surrogate_fd[1] = -1;
+			return( -1 );
+		}
+	}
+
+#else /* !SHELL_SURROGATE_PARENT */
+
+	fflush( NULL );
+# ifdef HAVE_THR
+	pid = fork1();
+# else
+	pid = fork();
+# endif
+	if ( pid == 0 ) {		/* child */
 		/*
 		 * child could deadlock here due to resources locked
 		 * by our parent
 		 *
-		 * If so, configure --without-threads or implement forking
-		 * via a surrogate parent.
+		 * If so, configure --without-threads.
 		 */
-		close( p2c[1] );
-		close( c2p[0] );
 		if ( dup2( p2c[0], 0 ) == -1 || dup2( c2p[1], 1 ) == -1 ) {
 			Debug( LDAP_DEBUG_ANY, "dup2 failed\n", 0, 0, 0 );
 			exit( EXIT_FAILURE );
 		}
-
+	}
+	close( p2c[0] );
+	close( c2p[1] );
+	if ( pid <= 0 ) {
+		close( p2c[1] );
+		close( c2p[0] );
+	}
+	switch ( pid ) {
+	case 0:
 		execv( args[0], args );

 		Debug( LDAP_DEBUG_ANY, "execv failed\n", 0, 0, 0 );
@ -66,13 +337,11 @@ forkandexec(
 	case -1:	/* trouble */
 		Debug( LDAP_DEBUG_ANY, "fork failed\n", 0, 0, 0 );
 		return( -1 );
-
-	default:	/* parent */
-		close( p2c[0] );
-		close( c2p[1] );
-		break;
 	}

+#endif /* SHELL_SURROGATE_PARENT */
+
+	/* parent */
 	if ( (*rfp = fdopen( c2p[0], "r" )) == NULL || (*wfp = fdopen( p2c[1],
 	    "w" )) == NULL ) {
 		Debug( LDAP_DEBUG_ANY, "fdopen failed\n", 0, 0, 0 );
--- a/servers/slapd/back-shell/init.c
+++ b/servers/slapd/back-shell/init.c
@ -10,6 +10,7 @@
 #include <stdio.h>

 #include <ac/socket.h>
+#include <ac/unistd.h>

 #include "slap.h"
 #include "shell.h"
@ -37,7 +38,7 @@ shell_back_initialize(
 	bi->bi_open = 0;
 	bi->bi_config = 0;
 	bi->bi_close = 0;
-	bi->bi_destroy = 0;
+	bi->bi_destroy = shell_back_destroy;

 	bi->bi_db_init = shell_back_db_init;
 	bi->bi_db_config = shell_back_db_config;
@ -64,6 +65,32 @@ shell_back_initialize(
 	bi->bi_connection_init = 0;
 	bi->bi_connection_destroy = 0;

+#ifdef SHELL_SURROGATE_PARENT
+	ldap_pvt_thread_mutex_init( &shell_surrogate_index_mutex );
+	ldap_pvt_thread_mutex_init( &shell_surrogate_fd_mutex[0] );
+	ldap_pvt_thread_mutex_init( &shell_surrogate_fd_mutex[1] );
+#endif
+
+	return 0;
+}
+
+int
+shell_back_destroy(
+	BackendInfo *bi
+)
+{
+#ifdef SHELL_SURROGATE_PARENT
+	ldap_pvt_thread_mutex_destroy( &shell_surrogate_index_mutex );
+	ldap_pvt_thread_mutex_destroy( &shell_surrogate_fd_mutex[0] );
+	ldap_pvt_thread_mutex_destroy( &shell_surrogate_fd_mutex[1] );
+	if ( shell_surrogate_fd[0] >= 0 ) {
+		close( shell_surrogate_fd[0] );
+		close( shell_surrogate_fd[1] );
+	}
+	if ( shell_surrogate_pid >= 0 )
+		kill( shell_surrogate_pid, SIGTERM );
+#endif
+
 	return 0;
 }

@ -74,6 +101,11 @@ shell_back_db_init(
 {
 	struct shellinfo	*si;

+#ifdef SHELL_SURROGATE_PARENT
+	if ( shell_surrogate_fd[0] < 0 )
+		make_surrogate_parent();
+#endif
+
 	si = (struct shellinfo *) ch_calloc( 1, sizeof(struct shellinfo) );

 	be->be_private = si;
--- a/servers/slapd/back-shell/modify.c
+++ b/servers/slapd/back-shell/modify.c
@ -30,7 +30,7 @@ shell_back_modify(
 	FILE			*rfp, *wfp;
 	int			i;

-	if ( si->si_modify == NULL ) {
+	if ( IS_NULLCMD( si->si_modify ) ) {
 		send_ldap_result( conn, op, LDAP_UNWILLING_TO_PERFORM, NULL,
 		    "modify not implemented", NULL, NULL );
 		return( -1 );
--- a/servers/slapd/back-shell/modrdn.c
+++ b/servers/slapd/back-shell/modrdn.c
@ -45,7 +45,7 @@ shell_back_modrdn(
 	struct shellinfo	*si = (struct shellinfo *) be->be_private;
 	FILE			*rfp, *wfp;

-	if ( si->si_modrdn == NULL ) {
+	if ( IS_NULLCMD( si->si_modrdn ) ) {
 		send_ldap_result( conn, op, LDAP_UNWILLING_TO_PERFORM, NULL,
 		    "modrdn not implemented", NULL, NULL );
 		return( -1 );
--- a/servers/slapd/back-shell/search.c
+++ b/servers/slapd/back-shell/search.c
@ -33,11 +33,10 @@ shell_back_search(
 )
 {
 	struct shellinfo	*si = (struct shellinfo *) be->be_private;
-	int 			i;
 	FILE			*rfp, *wfp;
 	AttributeName		*an;

-	if ( si->si_search == NULL ) {
+	if ( IS_NULLCMD( si->si_search ) ) {
 		send_ldap_result( conn, op, LDAP_UNWILLING_TO_PERFORM, NULL,
 		    "search not implemented", NULL, NULL );
 		return( -1 );
--- a/servers/slapd/back-shell/shell.h
+++ b/servers/slapd/back-shell/shell.h
@ -12,16 +12,41 @@

 LDAP_BEGIN_DECL

+#if defined(HAVE_RECVMSG) && !defined(NO_THREADS)
+#  define SHELL_SURROGATE_PARENT
+#endif
+
+#ifdef SHELL_SURROGATE_PARENT
+
+extern ldap_pvt_thread_mutex_t shell_surrogate_index_mutex;
+extern ldap_pvt_thread_mutex_t shell_surrogate_fd_mutex[2];
+extern int                     shell_surrogate_fd[2];
+extern pid_t                   shell_surrogate_pid;
+
+typedef struct berval Cmd_info;
+#define MAKE_CMD_INFO(args)  make_cmd_info( args )
+#define IS_NULLCMD(cmd)      ((cmd).bv_val == NULL)
+
+extern void make_surrogate_parent LDAP_P(( void ));
+
+#else /* !SHELL_SURROGATE_PARENT */
+
+typedef char **Cmd_info;
+#define MAKE_CMD_INFO(args)  charray_dup( args )
+#define IS_NULLCMD(cmd)      ((cmd) == NULL)
+
+#endif /* SHELL_SURROGATE_PARENT */
+
 struct shellinfo {
-	char	**si_bind;	/* cmd + args to exec for bind	  */
-	char	**si_unbind;	/* cmd + args to exec for unbind  */
-	char	**si_search;	/* cmd + args to exec for search  */
-	char	**si_compare;	/* cmd + args to exec for compare */
-	char	**si_modify;	/* cmd + args to exec for modify  */
-	char	**si_modrdn;	/* cmd + args to exec for modrdn  */
-	char	**si_add;	/* cmd + args to exec for add	  */
-	char	**si_delete;	/* cmd + args to exec for delete  */
-	char	**si_abandon;	/* cmd + args to exec for abandon */
+	Cmd_info si_bind;	/* cmd + args to exec for bind	  */
+	Cmd_info si_unbind;	/* cmd + args to exec for unbind  */
+	Cmd_info si_search;	/* cmd + args to exec for search  */
+	Cmd_info si_compare;	/* cmd + args to exec for compare */
+	Cmd_info si_modify;	/* cmd + args to exec for modify  */
+	Cmd_info si_modrdn;	/* cmd + args to exec for modrdn  */
+	Cmd_info si_add;	/* cmd + args to exec for add	  */
+	Cmd_info si_delete;	/* cmd + args to exec for delete  */
+	Cmd_info si_abandon;	/* cmd + args to exec for abandon */
 };

 struct slap_backend_db;
@ -29,7 +54,7 @@ struct slap_conn;
 struct slap_op;

 extern pid_t forkandexec LDAP_P((
-	char **args,
+	Cmd_info args,
 	FILE **rfp,
 	FILE **wfp));

--- a/servers/slapd/back-shell/unbind.c
+++ b/servers/slapd/back-shell/unbind.c
@ -25,7 +25,7 @@ shell_back_unbind(
 	struct shellinfo	*si = (struct shellinfo *) be->be_private;
 	FILE			*rfp, *wfp;

-	if ( si->si_unbind == NULL ) {
+	if ( IS_NULLCMD( si->si_unbind ) ) {
 		return 0;
 	}