make these use setres[ug]id for simple privilege dropping;

ok deraadt@ millert@ moritz@

12 files changed, 102 insertions, 84 deletions

diff --git a/usr.bin/fstat/fstat.c b/usr.bin/fstat/fstat.c
index 88c5b088387..3c231a9ea55 100644
--- a/usr.bin/fstat/fstat.c
+++ b/usr.bin/fstat/fstat.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: fstat.c,v 1.51 2005/05/26 05:15:56 tedu Exp $	*/
+/*	$OpenBSD: fstat.c,v 1.52 2005/07/04 01:54:09 djm Exp $	*/
 
 /*-
  * Copyright (c) 1988, 1993
@@ -37,7 +37,7 @@ static char copyright[] =
 
 #ifndef lint
 /*static char sccsid[] = "from: @(#)fstat.c	8.1 (Berkeley) 6/6/93";*/
-static char *rcsid = "$OpenBSD: fstat.c,v 1.51 2005/05/26 05:15:56 tedu Exp $";
+static char *rcsid = "$OpenBSD: fstat.c,v 1.52 2005/07/04 01:54:09 djm Exp $";
 #endif /* not lint */
 
 #include <sys/param.h>
@@ -174,6 +174,7 @@ main(int argc, char *argv[])
 	char *memf, *nlistf;
 	char buf[_POSIX2_LINE_MAX];
 	int cnt;
+	gid_t gid;
 
 	arg = 0;
 	what = KERN_PROC_ALL;
@@ -225,16 +226,17 @@ main(int argc, char *argv[])
 	 * Discard setgid privileges if not the running kernel so that bad
 	 * guys can't print interesting stuff from kernel memory.
 	 */
-	if (nlistf != NULL || memf != NULL) {
-		setegid(getgid());
-		setgid(getgid());
-	}
+	gid = getgid();
+	if (nlistf != NULL || memf != NULL)
+		if (setresgid(gid, gid, gid) == -1)
+			err(1, "setresgid");
 
 	if ((kd = kvm_openfiles(nlistf, memf, NULL, O_RDONLY, buf)) == NULL)
 		errx(1, "%s", buf);
 
-	setegid(getgid());
-	setgid(getgid());
+	if (nlistf == NULL && memf == NULL)
+		if (setresgid(gid, gid, gid) == -1)
+			err(1, "setresgid");
 
 	if (*(argv += optind)) {
 		for (; *argv; ++argv) {
diff --git a/usr.bin/modstat/modstat.c b/usr.bin/modstat/modstat.c
index d3934849f28..1eb46177998 100644
--- a/usr.bin/modstat/modstat.c
+++ b/usr.bin/modstat/modstat.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: modstat.c,v 1.21 2003/06/10 22:20:48 deraadt Exp $	*/
+/*	$OpenBSD: modstat.c,v 1.22 2005/07/04 01:54:10 djm Exp $	*/
 
 /*
  * Copyright (c) 1993 Terrence R. Lambert.
@@ -114,6 +114,7 @@ main(int argc, char *argv[])
 	char *modname = NULL;
 	char *endptr;
 	int devfd;
+	gid_t gid;
 
 	while ((c = getopt(argc, argv, "i:n:")) != -1) {
 		switch (c) {
@@ -143,8 +144,9 @@ main(int argc, char *argv[])
 	if ((devfd = open(_PATH_LKM, O_RDONLY)) == -1)
 		err(2, "%s", _PATH_LKM);
 
-	setegid(getgid());
-	setgid(getgid());
+	gid = getgid();
+	if (setresgid(gid, gid, gid) == -1)
+		err(1, "setresgid");
 
 	printf("Type     Id Off %-*s Size %-*s Rev Module Name\n",
 	    POINTERSIZE, "Loadaddr", POINTERSIZE, "Info");
diff --git a/usr.bin/msgs/msgs.c b/usr.bin/msgs/msgs.c
index 66091e883cb..d16e6fa93e4 100644
--- a/usr.bin/msgs/msgs.c
+++ b/usr.bin/msgs/msgs.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: msgs.c,v 1.29 2004/10/02 04:14:39 deraadt Exp $	*/
+/*	$OpenBSD: msgs.c,v 1.30 2005/07/04 01:54:10 djm Exp $	*/
 /*	$NetBSD: msgs.c,v 1.7 1995/09/28 06:57:40 tls Exp $	*/
 
 /*-
@@ -40,7 +40,7 @@ static char copyright[] =
 #if 0
 static char sccsid[] = "@(#)msgs.c	8.2 (Berkeley) 4/28/95";
 #else
-static char rcsid[] = "$OpenBSD: msgs.c,v 1.29 2004/10/02 04:14:39 deraadt Exp $";
+static char rcsid[] = "$OpenBSD: msgs.c,v 1.30 2005/07/04 01:54:10 djm Exp $";
 #endif
 #endif /* not lint */
 
@@ -173,8 +173,11 @@ main(int argc, char *argv[])
 #endif
 
 	time(&t);
-	seteuid(uid = getuid());
-	setuid(uid);
+	uid = getuid();
+	if (setresuid(uid, uid, uid) == -1) {
+		perror("setresuid");
+		exit(1);
+	}
 	ruptible = (signal(SIGINT, SIG_IGN) == SIG_DFL);
 	if (ruptible)
 		signal(SIGINT, SIG_DFL);
diff --git a/usr.bin/netstat/main.c b/usr.bin/netstat/main.c
index 6f024a1a734..bc69a48afa4 100644
--- a/usr.bin/netstat/main.c
+++ b/usr.bin/netstat/main.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: main.c,v 1.60 2005/06/16 16:03:32 jaredy Exp $	*/
+/*	$OpenBSD: main.c,v 1.61 2005/07/04 01:54:10 djm Exp $	*/
 /*	$NetBSD: main.c,v 1.9 1996/05/07 02:55:02 thorpej Exp $	*/
 
 /*
@@ -40,7 +40,7 @@ char copyright[] =
 #if 0
 static char sccsid[] = "from: @(#)main.c	8.4 (Berkeley) 3/1/94";
 #else
-static char *rcsid = "$OpenBSD: main.c,v 1.60 2005/06/16 16:03:32 jaredy Exp $";
+static char *rcsid = "$OpenBSD: main.c,v 1.61 2005/07/04 01:54:10 djm Exp $";
 #endif
 #endif /* not lint */
 
@@ -52,6 +52,7 @@ static char *rcsid = "$OpenBSD: main.c,v 1.60 2005/06/16 16:03:32 jaredy Exp $";
 #include <netinet/in.h>
 
 #include <ctype.h>
+#include <err.h>
 #include <errno.h>
 #include <kvm.h>
 #include <limits.h>
@@ -255,6 +256,7 @@ main(int argc, char *argv[])
 	int ch;
 	char *nlistf = NULL, *memf = NULL, *ep;
 	char buf[_POSIX2_LINE_MAX];
+	gid_t gid;
 	u_long pcbaddr = 0;
 
 	af = AF_UNSPEC;
@@ -390,18 +392,20 @@ main(int argc, char *argv[])
 	 * guys can't print interesting stuff from kernel memory.
 	 * Dumping PCB info is also restricted.
 	 */
-	if (nlistf != NULL || memf != NULL || Pflag) {
-		setegid(getgid());
-		setgid(getgid());
-	}
+	gid = getgid();
+	if (nlistf != NULL || memf != NULL || Pflag)
+		if (setresgid(gid, gid, gid) == -1)
+			err(1, "setresgid");
 
 	if ((kvmd = kvm_openfiles(nlistf, memf, NULL, O_RDONLY,
 	    buf)) == NULL) {
 		fprintf(stderr, "%s: kvm_open: %s\n", __progname, buf);
 		exit(1);
 	}
-	setegid(getgid());
-	setgid(getgid());
+
+	if (nlistf == NULL && memf == NULL && !Pflag)
+		if (setresgid(gid, gid, gid) == -1)
+			err(1, "setresgid");
 
 #define	BACKWARD_COMPATIBILITY
 #ifdef	BACKWARD_COMPATIBILITY
diff --git a/usr.bin/oldrdist/server.c b/usr.bin/oldrdist/server.c
index db1c6d6a7aa..775201b9329 100644
--- a/usr.bin/oldrdist/server.c
+++ b/usr.bin/oldrdist/server.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: server.c,v 1.28 2005/04/13 02:33:08 deraadt Exp $	*/
+/*	$OpenBSD: server.c,v 1.29 2005/07/04 01:54:10 djm Exp $	*/
 
 /*
  * Copyright (c) 1983, 1993
@@ -31,7 +31,7 @@
 
 #ifndef lint
 /* from: static char sccsid[] = "@(#)server.c	8.1 (Berkeley) 6/9/93"; */
-static char *rcsid = "$OpenBSD: server.c,v 1.28 2005/04/13 02:33:08 deraadt Exp $";
+static char *rcsid = "$OpenBSD: server.c,v 1.29 2005/07/04 01:54:10 djm Exp $";
 #endif /* not lint */
 
 #include <sys/wait.h>
@@ -1389,10 +1389,10 @@ dospecial(cmd)
 		(void) close(fd[0]);
 		(void) close(fd[1]);
 #if	defined(DIRECT_RCMD)
-		setegid(groupid);
-		setgid(groupid);
-		seteuid(userid);
-		setuid(userid);
+		if (setgroups(1, &groupid) == -1 ||
+		    setresgid(groupid, groupid, groupid) == -1 ||
+		    setresuid(userid, userid, userid) == -1)
+			_exit(127);
 #endif	/* DIRECT_RCMD */
 		execl(_PATH_BSHELL, "sh", "-c", cmd, (char *)NULL);
 		_exit(127);
diff --git a/usr.bin/rsh/rsh.c b/usr.bin/rsh/rsh.c
index 6a18aa836cf..39a693501de 100644
--- a/usr.bin/rsh/rsh.c
+++ b/usr.bin/rsh/rsh.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: rsh.c,v 1.37 2005/04/01 04:06:40 deraadt Exp $	*/
+/*	$OpenBSD: rsh.c,v 1.38 2005/07/04 01:54:10 djm Exp $	*/
 
 /*-
  * Copyright (c) 1983, 1990 The Regents of the University of California.
@@ -37,7 +37,7 @@ static const char copyright[] =
 
 #ifndef lint
 /*static const char sccsid[] = "from: @(#)rsh.c	5.24 (Berkeley) 7/1/91";*/
-static const char rcsid[] = "$OpenBSD: rsh.c,v 1.37 2005/04/01 04:06:40 deraadt Exp $";
+static const char rcsid[] = "$OpenBSD: rsh.c,v 1.38 2005/07/04 01:54:10 djm Exp $";
 #endif /* not lint */
 
 #include <sys/types.h>
@@ -77,10 +77,11 @@ main(int argc, char *argv[])
 	struct passwd *pw;
 	struct servent *sp;
 	sigset_t mask, omask;
-	int argoff = 0, asrsh = 0, ch, dflag = 0, nflag = 0, one = 1, rem, uid;
+	int argoff = 0, asrsh = 0, ch, dflag = 0, nflag = 0, one = 1, rem;
 	char *args, *host = NULL, *user = NULL;
 	pid_t pid = 0;
 	extern char *__progname;
+	uid_t uid;
 
 	/* if called as something other than "rsh", use it as the host name */
 	if (strcmp(__progname, "rsh") != 0)
@@ -116,14 +117,16 @@ main(int argc, char *argv[])
 		}
 	optind += argoff;
 
+	uid = getuid();
+
 	/* if haven't gotten a host yet, do so */
 	if (!host && !(host = argv[optind++]))
 		usage();
 
 	/* if no command, login to remote host via ssh. */
 	if (!argv[optind]) {
-		seteuid(getuid());
-		setuid(getuid());
+		if (setresuid(uid, uid, uid) == -1)
+			err(1, "setresuid");
 		if (asrsh)
 			*argv = "ssh";
 		execv(_PATH_SSH, argv);
@@ -135,7 +138,7 @@ main(int argc, char *argv[])
 
 	if (geteuid() != 0)
 		errx(1, "must be setuid root");
-	if ((pw = getpwuid(uid = getuid())) == NULL)
+	if ((pw = getpwuid(uid)) == NULL)
 		errx(1, "unknown user ID %u", uid);
 	if (user == NULL)
 		user = pw->pw_name;
@@ -154,8 +157,8 @@ main(int argc, char *argv[])
 	if (rfd2 < 0)
 		errx(1, "can't establish stderr");
 
-	(void)seteuid(uid);
-	(void)setuid(uid);
+	if (setresuid(uid, uid, uid) == -1)
+		err(1, "setresuid");
 
 	if (dflag) {
 		if (setsockopt(rem, SOL_SOCKET, SO_DEBUG, &one,
diff --git a/usr.bin/sup/src/run.c b/usr.bin/sup/src/run.c
index b49a4bdc668..c96a592dfa8 100644
--- a/usr.bin/sup/src/run.c
+++ b/usr.bin/sup/src/run.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: run.c,v 1.13 2002/06/12 06:07:16 mpech Exp $	*/
+/*	$OpenBSD: run.c,v 1.14 2005/07/04 01:54:10 djm Exp $	*/
 
 /*
  * Copyright (c) 1991 Carnegie Mellon University
@@ -170,15 +170,19 @@ dorun(name, argv, usepath)
 	pid_t pid;
 	struct sigaction ignoresig, intsig, quitsig;
 	int status;
+	uid_t uid;
+	gid_t gid;
 
 	if ((pid = fork()) == -1)
 		return(-1);	/* no more process's, so exit with error */
 
 	if (pid == 0) {			/* child process */
-		setegid(getgid());
-		setgid(getgid());
-		seteuid(getuid());
-		setuid(getuid());
+		uid = getuid();
+		gid = getgid();
+		if (setgroups(1, &gid) == -1 ||
+		    setresgid(gid, gid, gid) == -1 ||
+		    setresuid(uid, uid, uid) == -1)
+			_exit(0377);
 		if (usepath)
 		    execvp(name,argv);
 		else
diff --git a/usr.bin/sup/src/supfilesrv.c b/usr.bin/sup/src/supfilesrv.c
index 31709e08f20..e90432e1bd7 100644
--- a/usr.bin/sup/src/supfilesrv.c
+++ b/usr.bin/sup/src/supfilesrv.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: supfilesrv.c,v 1.34 2004/05/31 15:48:26 pedro Exp $	*/
+/*	$OpenBSD: supfilesrv.c,v 1.35 2005/07/04 01:54:10 djm Exp $	*/
 
 /*
  * Copyright (c) 1992 Carnegie Mellon University
@@ -1852,14 +1852,10 @@ changeuid(namep, passwordp, fileuid, filegid)
 #if	CMUCS
 	if (setgroups(grps[0], &grps[1]) < 0)
 		logerr("setgroups: %%m");
-	if (setegid((gid_t)grp->gr_gid) < 0)
-		logerr("setegid: %%m");
-	if (setgid((gid_t)grp->gr_gid) < 0)
-		logerr("setgid: %%m");
-	if (seteuid(pwd->pw_uid) < 0)
-		logerr("seteuid: %%m");
-	if (setuid(pwd->pw_uid) < 0)
-		logerr("setuid: %%m");
+	if (setresgid(grp->gr_gid, grp->gr_gid, grp->gr_gid) < 0)
+		logerr("setresgid: %%m");
+	if (setresuid(pwd->pw_uid, pwd->pw_uid, pwd->pw_uid) < 0)
+		logerr("setresuid: %%m");
 #else   /* CMUCS */
 #ifdef HAS_LOGIN_CAP
 	if (setusercontext(NULL, pwd, pwd->pw_uid, LOGIN_SETALL) < 0)
@@ -1867,18 +1863,14 @@ changeuid(namep, passwordp, fileuid, filegid)
 #else
 	if (initgroups(pwd->pw_name,pwd->pw_gid) < 0)
 		return ("Error setting group list");
-	if (setegid(pwd->pw_gid) < 0)
-		logerr("setegid: %%m");
-	if (setgid(pwd->pw_gid) < 0)
-		logerr("setgid: %%m");
+	if (setresgid(pwd->pw_gid, pwd->pw_gid, pwd->pw_gid) < 0)
+		logerr("setresgid: %%m");
 #ifndef NO_SETLOGIN
 	if (setlogin(pwd->pw_name) < 0)
 		logerr("setlogin: %%m");
 #endif
-	if (seteuid(pwd->pw_uid) < 0)
-		logerr("seteuid: %%m");
-	if (setuid(pwd->pw_uid) < 0)
-		logerr("setuid: %%m");
+	if (setresuid(pwd->pw_uid, pwd->pw_uid, pwd->pw_uid) < 0)
+		logerr("setresuid: %%m");
 #endif	/* HAS_LOGIN_CAP */
 #endif	/* CMUCS */
 	return (NULL);
diff --git a/usr.bin/systat/main.c b/usr.bin/systat/main.c
index 78e5acf5ee2..f74c6647eb6 100644
--- a/usr.bin/systat/main.c
+++ b/usr.bin/systat/main.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: main.c,v 1.30 2004/04/26 19:22:30 itojun Exp $	*/
+/*	$OpenBSD: main.c,v 1.31 2005/07/04 01:54:10 djm Exp $	*/
 /*	$NetBSD: main.c,v 1.8 1996/05/10 23:16:36 thorpej Exp $	*/
 
 /*-
@@ -40,7 +40,7 @@ static char copyright[] =
 #if 0
 static char sccsid[] = "@(#)main.c	8.1 (Berkeley) 6/6/93";
 #endif
-static char rcsid[] = "$OpenBSD: main.c,v 1.30 2004/04/26 19:22:30 itojun Exp $";
+static char rcsid[] = "$OpenBSD: main.c,v 1.31 2005/07/04 01:54:10 djm Exp $";
 #endif /* not lint */
 
 #include <sys/param.h>
@@ -87,6 +87,7 @@ main(int argc, char *argv[])
 {
 	int ch;
 	char errbuf[_POSIX2_LINE_MAX];
+	gid_t gid;
 
 	kd = kvm_openfiles(NULL, NULL, NULL, O_RDONLY, errbuf);
 	if (kd == NULL) {
@@ -94,8 +95,9 @@ main(int argc, char *argv[])
 		exit(1);
 	}
 
-	setegid(getgid());
-	setgid(getgid());
+	gid = getgid();
+	if (setresgid(gid, gid, gid) == -1)
+		err(1, "setresgid");
 
 	while ((ch = getopt(argc, argv, "nw:")) != -1)
 		switch (ch) {
diff --git a/usr.bin/vmstat/dkstats.c b/usr.bin/vmstat/dkstats.c
index 2b58fe53304..d27244d5f71 100644
--- a/usr.bin/vmstat/dkstats.c
+++ b/usr.bin/vmstat/dkstats.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: dkstats.c,v 1.25 2004/04/22 22:28:37 millert Exp $	*/
+/*	$OpenBSD: dkstats.c,v 1.26 2005/07/04 01:54:10 djm Exp $	*/
 /*	$NetBSD: dkstats.c,v 1.1 1996/05/10 23:19:27 thorpej Exp $	*/
 
 /*
@@ -409,16 +409,17 @@ dkinit(int select)
 	size_t		size;
 	struct clockinfo clkinfo;
 	char		*disknames, *name, *bufpp;
+	gid_t		gid;
 
 	if (once)
 		return(1);
 
+	gid = getgid();
 	if (nlistf != NULL || memf != NULL) {
 #if !defined(NOKVM)
-		if (memf != NULL) {
-			setegid(getgid());
-			setgid(getgid());
-		}
+		if (memf != NULL)
+			if (setresgid(gid, gid, gid) == -1)
+				err(1, "setresgid");
 
 		/* Open the kernel. */
 		if (kd == NULL &&
@@ -426,8 +427,9 @@ dkinit(int select)
 		    errbuf)) == NULL)
 			errx(1, "kvm_openfiles: %s", errbuf);
 
-		setegid(getgid());
-		setgid(getgid());
+		if (memf == NULL)
+			if (setresgid(gid, gid, gid) == -1)
+				err(1, "setresgid");
 
 		/* Obtain the namelist symbols from the kernel. */
 		if (kvm_nlist(kd, namelist))
diff --git a/usr.bin/vmstat/vmstat.c b/usr.bin/vmstat/vmstat.c
index 31bb4233d6d..d989e1a0fd9 100644
--- a/usr.bin/vmstat/vmstat.c
+++ b/usr.bin/vmstat/vmstat.c
@@ -1,5 +1,5 @@
 /*	$NetBSD: vmstat.c,v 1.29.4.1 1996/06/05 00:21:05 cgd Exp $	*/
-/*	$OpenBSD: vmstat.c,v 1.95 2005/04/21 04:42:56 mickey Exp $	*/
+/*	$OpenBSD: vmstat.c,v 1.96 2005/07/04 01:54:10 djm Exp $	*/
 
 /*
  * Copyright (c) 1980, 1986, 1991, 1993
@@ -40,7 +40,7 @@ static char copyright[] =
 #if 0
 static char sccsid[] = "@(#)vmstat.c	8.1 (Berkeley) 6/6/93";
 #else
-static const char rcsid[] = "$OpenBSD: vmstat.c,v 1.95 2005/04/21 04:42:56 mickey Exp $";
+static const char rcsid[] = "$OpenBSD: vmstat.c,v 1.96 2005/07/04 01:54:10 djm Exp $";
 #endif
 #endif /* not lint */
 
@@ -151,6 +151,7 @@ main(int argc, char *argv[])
 	u_int interval;
 	int reps;
 	char errbuf[_POSIX2_LINE_MAX];
+	gid_t gid;
 
 	interval = reps = todo = 0;
 	while ((c = getopt(argc, argv, "c:fiM:mN:stw:vz")) != -1) {
@@ -199,9 +200,10 @@ main(int argc, char *argv[])
 	if (todo == 0)
 		todo = VMSTAT;
 
+	gid = getgid();
 	if (nlistf != NULL || memf != NULL) {
-		setegid(getgid());
-		setgid(getgid());
+		if (setresgid(gid, gid, gid) == -1)
+			err(1, "setresgid");
 	}
 
 	/*
@@ -215,9 +217,11 @@ main(int argc, char *argv[])
 		if (kd == 0)
 			errx(1, "kvm_openfiles: %s", errbuf);
 
+		if (nlistf == NULL && memf == NULL)
+			if (setresgid(gid, gid, gid) == -1)
+				err(1, "setresgid");
+
 		if ((c = kvm_nlist(kd, namelist)) != 0) {
-			setgid(getgid());
-			setegid(getegid());
 
 			if (c > 0) {
 				(void)fprintf(stderr,
@@ -234,12 +238,10 @@ main(int argc, char *argv[])
 				errx(1, "kvm_nlist: %s", kvm_geterr(kd));
 		}
 #ifdef notyet
-	}
+	} else if (setresgid(gid, gid, gid) == -1)
+		err(1, "setresgid");
 #endif /* notyet */
 
-	setegid(getegid());
-	setgid(getgid());
-
 	mib[0] = CTL_HW;
 	mib[1] = HW_NCPU;
 	size = sizeof(ncpu);
diff --git a/usr.bin/write/write.c b/usr.bin/write/write.c
index 70c4b8e434a..442abdcd23d 100644
--- a/usr.bin/write/write.c
+++ b/usr.bin/write/write.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: write.c,v 1.22 2003/07/10 00:06:52 david Exp $	*/
+/*	$OpenBSD: write.c,v 1.23 2005/07/04 01:54:11 djm Exp $	*/
 /*	$NetBSD: write.c,v 1.5 1995/08/31 21:48:32 jtc Exp $	*/
 
 /*
@@ -43,7 +43,7 @@ static char copyright[] =
 #if 0
 static char sccsid[] = "@(#)write.c	8.2 (Berkeley) 4/27/95";
 #endif
-static char *rcsid = "$OpenBSD: write.c,v 1.22 2003/07/10 00:06:52 david Exp $";
+static char *rcsid = "$OpenBSD: write.c,v 1.23 2005/07/04 01:54:11 djm Exp $";
 #endif /* not lint */
 
 #include <sys/param.h>
@@ -240,6 +240,7 @@ do_write(char *tty, char *mytty, uid_t myuid)
 	struct passwd *pwd;
 	time_t now;
 	char path[MAXPATHLEN], host[MAXHOSTNAMELEN], line[512];
+	gid_t gid;
 
 	/* Determine our login name before the we reopen() stdout */
 	if ((login = getlogin()) == NULL) {
@@ -254,8 +255,9 @@ do_write(char *tty, char *mytty, uid_t myuid)
 		err(1, "%s", path);
 
 	/* revoke privs, now that we have opened the tty */
-	setegid(getgid());
-	setgid(getgid());
+	gid = getgid();
+	if (setresgid(gid, gid, gid) == -1)
+		err(1, "setresgid");
 
 	(void)signal(SIGINT, done);
 	(void)signal(SIGHUP, done);