add a special edition doas that only lets root drop privs.

maybe the installer can use something like this, wink wink.
ok deraadt

2 files changed, 113 insertions, 0 deletions

diff --git a/distrib/special/doas/Makefile b/distrib/special/doas/Makefile
new file mode 100644
index 00000000000..ae95c24ed68
--- /dev/null
+++ b/distrib/special/doas/Makefile
@@ -0,0 +1,6 @@
+#	$OpenBSD: Makefile,v 1.1 2016/08/16 04:55:33 tedu Exp $
+
+PROG=	doas
+SRCS=	doas.c
+
+.include <bsd.prog.mk>
diff --git a/distrib/special/doas/doas.c b/distrib/special/doas/doas.c
new file mode 100644
index 00000000000..42c4d80bbd0
--- /dev/null
+++ b/distrib/special/doas/doas.c
@@ -0,0 +1,107 @@
+/* $OpenBSD: doas.c,v 1.1 2016/08/16 04:55:33 tedu Exp $ */
+/*
+ * Copyright (c) 2015 Ted Unangst <tedu@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include <limits.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <err.h>
+#include <unistd.h>
+#include <pwd.h>
+#include <grp.h>
+#include <syslog.h>
+#include <errno.h>
+
+static void __dead
+usage(void)
+{
+	fprintf(stderr, "usage: doas [-u user] command [args]\n");
+	exit(1);
+}
+
+static int
+parseuid(const char *s, uid_t *uid)
+{
+	struct passwd *pw;
+	const char *errstr;
+
+	if ((pw = getpwnam(s)) != NULL) {
+		*uid = pw->pw_uid;
+		return 0;
+	}
+	*uid = strtonum(s, 0, UID_MAX, &errstr);
+	if (errstr)
+		return -1;
+	return 0;
+}
+
+int
+main(int argc, char **argv)
+{
+	const char *cmd;
+	struct passwd *pw;
+	uid_t uid;
+	uid_t target = 0;
+	gid_t groups[1];
+	int ngroups;
+	int i, ch;
+
+	setprogname("doas");
+
+	closefrom(STDERR_FILENO + 1);
+
+	uid = getuid();
+	if (uid != 0)
+		errc(1, EPERM, "root only");
+
+	while ((ch = getopt(argc, argv, "u:")) != -1) {
+		switch (ch) {
+		case 'u':
+			if (parseuid(optarg, &target) != 0)
+				errx(1, "unknown user");
+			break;
+		default:
+			usage();
+			break;
+		}
+	}
+	argv += optind;
+	argc -= optind;
+
+	if (!argc)
+		usage();
+
+	cmd = argv[0];
+
+	pw = getpwuid(target);
+	if (!pw)
+		errx(1, "no passwd entry for target");
+	groups[0] = pw->pw_gid;
+
+	if (setgroups(1, groups) ||
+	    setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) ||
+	    setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid))
+		err(1, "failed to change user"); 
+
+	execvp(cmd, argv);
+	if (errno == ENOENT)
+		errx(1, "%s: command not found", cmd);
+	err(1, "%s", cmd);
+}