1 files changed, 280 insertions, 0 deletions
diff --git a/sys-utils/switch_root.c b/sys-utils/switch_root.c
new file mode 100644
index 00000000..b192a08e
--- /dev/null
+++ b/sys-utils/switch_root.c
@@ -0,0 +1,280 @@
+/*
+ * switchroot.c - switch to new root directory and start init.
+ *
+ * Copyright 2002-2009 Red Hat, Inc.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors:
+ *	Peter Jones <pjones@redhat.com>
+ *	Jeremy Katz <katzj@redhat.com>
+ */
+#include <sys/mount.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/param.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <ctype.h>
+#include <dirent.h>
+#include <err.h>
+#include <libgen.h>
+
+#ifndef MS_MOVE
+#define MS_MOVE 8192
+#endif
+
+/* remove all files/directories below dirName -- don't cross mountpoints */
+static int recursiveRemove(int fd)
+{
+	struct stat rb;
+	DIR *dir;
+	int rc = -1;
+	int dfd;
+
+	if (!(dir = fdopendir(fd))) {
+		warn("failed to open directory");
+		goto done;
+	}
+
+	/* fdopendir() precludes us from continuing to use the input fd */
+	dfd = dirfd(dir);
+
+	if (fstat(dfd, &rb)) {
+		warn("failed to stat directory");
+		goto done;
+	}
+
+	while(1) {
+		struct dirent *d;
+
+		errno = 0;
+		if (!(d = readdir(dir))) {
+			if (errno) {
+				warn("failed to read directory");
+				goto done;
+			}
+			break;	/* end of directory */
+		}
+
+		if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
+			continue;
+
+		if (d->d_type == DT_DIR) {
+			struct stat sb;
+
+			if (fstatat(dfd, d->d_name, &sb, AT_SYMLINK_NOFOLLOW)) {
+				warn("failed to stat %s", d->d_name);
+				continue;
+			}
+
+			/* remove subdirectories if device is same as dir */
+			if (sb.st_dev == rb.st_dev) {
+				int cfd;
+
+				cfd = openat(dfd, d->d_name, O_RDONLY);
+				if (cfd >= 0) {
+					recursiveRemove(cfd);
+					close(cfd);
+				}
+			} else
+				continue;
+		}
+
+		if (unlinkat(dfd, d->d_name,
+			     d->d_type == DT_DIR ? AT_REMOVEDIR : 0))
+			warn("failed to unlink %s", d->d_name);
+	}
+
+	rc = 0;	/* success */
+
+done:
+	if (dir)
+		closedir(dir);
+	return rc;
+}
+
+/* find the enclosing mount point of a path, by examining the backing device
+ * of parent directories until we reach / or find a parent with a differing
+ * device. Result must be freed.
+ */
+static char *get_parent_mount(const char *path)
+{
+	struct stat sb;
+	char *dir;
+	char tmp[PATH_MAX];
+	dev_t inner_dev;
+
+	if (stat(path, &sb) != 0) {
+		warn("failed to stat %s", path);
+		return NULL;
+	}
+
+	inner_dev = sb.st_dev;
+	dir = strdup(path);
+
+	while (dir) {
+		char *parent;
+
+		strncpy(tmp, dir, PATH_MAX);
+		tmp[PATH_MAX - 1] = '\0';
+		parent = dirname(tmp);
+
+		if (stat(parent, &sb) != 0) {
+			warn("failed to stat %s", parent);
+			return NULL;
+		}
+		if (sb.st_dev != inner_dev)
+			return dir;
+
+		strncpy(dir, parent, PATH_MAX);
+		dir[PATH_MAX - 1] = '\0';
+
+		/* maybe we've reached / */
+		if (*dir == '/' && !*(dir + 1))
+			return dir;
+	}
+	return NULL;
+}
+
+static int switchroot(const char *newroot)
+{
+	/*  Don't try to unmount the old "/", there's no way to do it. */
+	const char *umounts[] = { "/dev", "/proc", "/sys", NULL };
+	int i;
+	int cfd, rc = -1;
+	pid_t pid;
+	const char *chroot_path = NULL;
+	char *newroot_mnt;
+
+	for (i = 0; umounts[i] != NULL; i++) {
+		char newmount[PATH_MAX];
+
+		snprintf(newmount, sizeof(newmount), "%s%s", newroot, umounts[i]);
+
+		if (mount(umounts[i], newmount, NULL, MS_MOVE, NULL) < 0) {
+			warn("failed to mount moving %s to %s",
+				umounts[i], newmount);
+			warnx("forcing unmount of %s", umounts[i]);
+			umount2(umounts[i], MNT_FORCE);
+		}
+	}
+
+	newroot_mnt = get_parent_mount(newroot);
+	if (newroot_mnt && strcmp(newroot, newroot_mnt)) {
+		/* newroot is not a mount point, so we have to MS_MOVE the
+		 * parent mount point and then chroot in to the "subroot"
+		 */
+		chroot_path = newroot + strlen(newroot_mnt);
+		newroot = newroot_mnt;
+	}
+
+	if (chdir(newroot)) {
+		warn("failed to change directory to %s", newroot);
+		goto done;
+	}
+
+	cfd = open("/", O_RDONLY);
+
+	if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
+		warn("failed to mount moving %s to /", newroot);
+		goto done;
+	}
+
+	/* move to the real root of the device */
+	if (chroot(".")) {
+		warn("failed to change root");
+		goto done;
+	}
+
+	/* move to the subdirectory on the root device (subroot) */
+	if (chroot_path) {
+		if (chdir(chroot_path)) {
+			warn("failed to chdir to subroot %s", chroot_path);
+			goto done;
+		}
+		if (chroot(".")) {
+			warn("failed to change root to subroot %s", chroot_path);
+			goto done;
+		}
+	}
+
+	if (cfd >= 0) {
+		pid = fork();
+		if (pid <= 0) {
+			recursiveRemove(cfd);
+			if (pid == 0)
+				exit(EXIT_SUCCESS);
+		}
+		close(cfd);
+	}
+	rc = 0;
+done:
+	free(newroot_mnt);
+	return rc;
+}
+
+static void usage(FILE *output)
+{
+	fprintf(output, "usage: %s <newrootdir> <init> <args to init>\n",
+			program_invocation_short_name);
+	exit(output == stderr ? EXIT_FAILURE : EXIT_SUCCESS);
+}
+
+static void version(void)
+{
+	fprintf(stdout,  "%s from %s\n", program_invocation_short_name,
+			PACKAGE_STRING);
+	exit(EXIT_SUCCESS);
+}
+
+int main(int argc, char *argv[])
+{
+	char *newroot, *init, **initargs;
+
+	if (argv[1] && (!strcmp(argv[1], "--help") || !strcmp(argv[1], "-h")))
+		usage(stdout);
+	if (argv[1] && (!strcmp(argv[1], "--version") || !strcmp(argv[1], "-V")))
+		version();
+	if (argc < 3)
+		usage(stderr);
+
+	newroot = argv[1];
+	init = argv[2];
+	initargs = &argv[2];
+
+	if (!*newroot || !*init)
+		usage(stderr);
+
+	if (switchroot(newroot))
+		errx(EXIT_FAILURE, "failed. Sorry.");
+
+	if (access(init, X_OK))
+		warn("cannot access %s", init);
+
+	/* get session leader */
+	setsid();
+
+	/* set controlling terminal */
+	if (ioctl (0, TIOCSCTTY, 1))
+		warn("failed to TIOCSCTTY");
+
+	execv(init, initargs);
+	err(EXIT_FAILURE, "failed to execute %s", init);
+}
+