PengDroid: a healthy fusion of Debian and Android

config.sh

#!/bin/sh

set -e -x

export PATH=$PATH:/usr/local/sbin:/usr/sbin:/sbin

mkdir -p /usr/share/man/man1
/var/lib/dpkg/info/dash.preinst install || true
dpkg --configure -a
ln -sf update-rc.d-insserv /usr/sbin/update-rc.d
dpkg --clear-selections
dpkg --set-selections < /selections
apt-get -u dselect-upgrade --purge
ln -sf update-rc.d-insserv /usr/sbin/update-rc.d
ln -sf /bin/sh /bin/bash
echo BotBrew > /etc/debian_chroot

mkdir /android
ln -s /android/system	/system
ln -s /android/data	/data
ln -s /android/cache	/cache

rm /config.sh
rm /selections
rm /usr/bin/qemu-arm-static

init.c

#include <libgen.h>
#include <getopt.h>
#include <stdio.h>
#include <stdlib.h>
#include <alloca.h>
#include <malloc.h>
#include <unistd.h>
#include <sched.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/mount.h>
#include <sys/types.h>
#include <sys/wait.h>

#include "strnstr.h"

#define ENV_PATH	"/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/local/games:/usr/games:/usr/libexec/busybox"

struct config {
	char *target;
	char *cwd;
	char *const *argv;
};

struct mountspec {
	char *src;
	char *dst;
	char *type;
	unsigned long flags;
	void *data;
	unsigned long remount_flags;
};

static struct mountspec foreign_mounts[] = {
	{NULL,"/proc","proc",0,NULL,0},
	{"/dev","/dev",NULL,MS_BIND,NULL,0},
	{"/dev/pts","/dev/pts",NULL,MS_BIND,NULL,0},
	{NULL,"/sys","sysfs",0,NULL,0},
	{NULL,"/android","tmpfs",MS_NODEV|MS_NOEXEC|MS_NOATIME,"size=1M,mode=0755",0},
	{"/cache","/android/cache",NULL,MS_BIND,NULL,0},
	{"/data","/android/data",NULL,MS_BIND,NULL,0},
	{"/emmc","/android/emmc",NULL,MS_BIND,NULL,0},
	{"/sd-ext","/android/sd-ext",NULL,MS_BIND,NULL,0},
	{"/sdcard","/android/sdcard",NULL,MS_BIND,NULL,0},
	{"/system","/android/system",NULL,MS_BIND,NULL,MS_REMOUNT|MS_NODEV|MS_NOATIME},
	{"/usbdisk","/android/usbdisk",NULL,MS_BIND,NULL,0},
	{"/system/xbin","/android/system/xbin",NULL,MS_BIND,NULL,MS_REMOUNT|MS_NODEV|MS_NOATIME}
};
static int n_foreign_mounts = sizeof(foreign_mounts)/sizeof(foreign_mounts[0]);

static void usage(char *progname) {
	fprintf(stderr,
		"Usage: %s [options] [--] [<command>...]\n"
		"\n"
		"Available options:\n"
		"\t-d <directory>\t| --dir=<directory>\tSpecify chroot directory\n",
	progname);
	exit(EXIT_FAILURE);
}

static void privdrop(void) {
	gid_t gid = getgid();
	uid_t uid = getuid();
	setgroups(1,&gid);
#ifdef linux
	setregid(gid,gid);
	setreuid(uid,uid);
#else
	setegid(gid);
	setgid(gid);
	seteuid(uid);
	setuid(uid);
#endif
}

static int main_clone(struct config *config) {
	char *initsh = alloca(snprintf(NULL,0,"%s/init.sh",config->target)+1);
	sprintf(initsh,"%s/init.sh",config->target);
	char cwd[PATH_MAX];
	if(getcwd(cwd,sizeof(cwd)) == NULL) {
		fprintf(stderr,"whoops: cannot get working directory\n");
		return EXIT_FAILURE;
	}
	if(chdir(config->target)) {
		fprintf(stderr,"whoops: cannot chdir to namespace\n");
		return EXIT_FAILURE;
	}
	size_t target_len = strlen(config->target);
	int i;
	for(i = 0; i < n_foreign_mounts; i++) {
		struct mountspec m = foreign_mounts[i];
		size_t dst_len = strlen(m.dst);
		char *dst = malloc(target_len+dst_len+1);
		memcpy(dst,config->target,target_len);
		memcpy(dst+target_len,m.dst,dst_len+1);	// includes null terminator
		mkdir(dst,0755);
		if(mount(m.src,dst,m.type,m.flags,m.data)) rmdir(dst);
		else if(m.remount_flags) mount(dst,dst,NULL,m.remount_flags|MS_REMOUNT,NULL);
		free(dst);
	}
	if(chroot(".")) {
		fprintf(stderr,"whoops: cannot chroot\n");
		return EXIT_FAILURE;
	}
	if((chdir(cwd))&&(chdir("/"))) {
		fprintf(stderr,"whoops: cannot chdir to chroot\n");
		return EXIT_FAILURE;
	}
	privdrop();
	char *env_path = getenv("PATH");
	if((env_path)&&(env_path[0])) {
		size_t env_path_len = strlen(env_path);
		char *newpath = malloc(sizeof(ENV_PATH)+env_path_len);
		char *append = strstr(env_path,"::");
		if(append) {	// break string at :: and insert
			append++;
			size_t prepend_len = append-env_path;
			memcpy(newpath,env_path,prepend_len);
			memcpy(newpath+prepend_len,ENV_PATH,sizeof(ENV_PATH)-1);
			memcpy(newpath+prepend_len+sizeof(ENV_PATH)-1,append,env_path_len-prepend_len+1);
		} else {
			memcpy(newpath,ENV_PATH":",sizeof(ENV_PATH":")-1);
			memcpy(newpath+sizeof(ENV_PATH":")-1,env_path,env_path_len+1);	// includes null terminator
		}
		setenv("PATH",newpath,1);
		free(newpath);
	} else setenv("PATH",ENV_PATH":/android/sbin:/system/sbin:/system/bin:/system/xbin",1);
	if(config->argv == NULL) {
		char *argv0[2];
		argv0[0] = "/init.sh";
		argv0[1] = 0;
		config->argv = (char**)&argv0;
	}
	if(execvp(config->argv[0],config->argv)) {
		int i = 1;
		fprintf(stderr,"whoops: cannot run `%s",config->argv[0]);
		while(config->argv[i]) fprintf(stderr," %s",config->argv[i++]);
		fprintf(stderr,"'\n");
		return errno;
	}
	return 0;	// wtf
}

int main(int argc, char *argv[]) {
	struct config config;
	struct stat st;
	char apath[PATH_MAX];
	// get absolute path
	config.target = realpath(dirname(argv[0]),apath);
	uid_t uid = getuid();
	int c;
	while(1) {
		static struct option long_options[] = {
			{"dir",required_argument,0,'d'},
			{0,0,0,0}
		};
		int option_index = 0;
		c = getopt_long(argc,argv,"d:",long_options,&option_index);
		if(c == -1) break;
		switch(c) {
			case 'd':
				// prevent privilege escalation: only superuser can chroot to arbitrary directories
				if(uid) {
					fprintf(stderr,"whoops: --dir is only available for uid=0\n");
					return EXIT_FAILURE;
				}
				config.target = realpath(optarg,apath);
				break;
			default:
				usage(argv[0]);
		}
	}
	config.argv = (optind==argc)?NULL:(argv+optind);
	// prevent privilege escalation: fail if link/symlink is not owned by superuser
	if(uid) {
		if(lstat(argv[0],&st)) {
			fprintf(stderr,"whoops: cannot stat `%s'\n",argv[0]);
			return EXIT_FAILURE;
		}
		if(st.st_uid) {
			fprintf(stderr,"whoops: `%s' is not owned by uid=0\n",argv[0]);
			return EXIT_FAILURE;
		}
	}
	// check if directory exists
	if((stat(config.target,&st))||(!S_ISDIR(st.st_mode))) {
		fprintf(stderr,"whoops: `%s' is not a directory\n",config.target);
		return EXIT_FAILURE;
	}
	if((st.st_uid)||(st.st_gid)) chown(config.target,0,0);
	if((st.st_mode&S_IWGRP)||(st.st_mode&S_IWOTH)) chmod(config.target,0755);
	// check if directory mounted
	FILE *fp;
	char *haystack;
	size_t len;
	size_t target_len = strlen(config.target);
	char *needle = malloc(target_len+3);
	needle[0] = needle[target_len+1] = ' ';
	memcpy(needle+1,config.target,target_len+1);	// includes null terminator
	int mounted = 0;
	if(fp = fopen("/proc/self/mounts","r")) while(haystack = fgetln(fp,&len)) if(strnstr(haystack,needle,len)) {
		mounted = 1;
		break;
	}
	free(needle);
	if(!mounted) {
		if(geteuid()) {
			fprintf(stderr,"whoops: superuser privileges required for first invocation of `%s'\n",argv[0]);
			return EXIT_FAILURE;
		}
		mount(config.target,config.target,NULL,MS_BIND,NULL);
		mount(config.target,config.target,NULL,MS_REMOUNT|MS_NODEV|MS_NOATIME,NULL);
		if(!stat(argv[0],&st)) {
			// setuid
			if((st.st_uid)||(st.st_gid)) chown(argv[0],0,0);
			if((st.st_mode&S_IWGRP)||(st.st_mode&S_IWOTH)||!(st.st_mode&S_ISUID)) chmod(argv[0],04755);
		}
	}
	// clone with new namespace
	long stacksz = sysconf(_SC_PAGESIZE);
	void *stack = alloca(stacksz)+stacksz;
	pid_t pid = clone(main_clone,stack,SIGCHLD|CLONE_NEWNS|CLONE_FILES,(void*)&config);
	if(pid < 0) {
		fprintf(stderr,"whoops: cannot clone\n");
		return EXIT_FAILURE;
	} else {
		int ret;
		privdrop();
		while((waitpid(pid,&ret,0)<0)&&(errno == EINTR));
		return WIFEXITED(ret)?WEXITSTATUS(ret):EXIT_FAILURE;
	}
}

init.sh

#!/system/bin/sh

case "$0" in
	/init.sh)
		exec /system/bin/sh
		;;
esac

multi-strap

[General]
arch		= armel
directory	= ./pengdroid/
cleanup		= true
noauth		= true
unpack		= true
debootstrap	= Grip
aptsources	= Grip
setupscript= ./setup.sh
configscript= ./config.sh

[Grip]
keyring		= emdebian-archive-keyring
source		= http://www.emdebian.org/grip
suite		= squeeze

selections

apt						install
coreutils					install
dash						install
debconf						install
debconf-i18n					install
debian-archive-keyring				install
debianutils					install
dpkg						install
emdebian-archive-keyring			install
findutils					install
gcc-4.4-base					install
gnupg						install
gpgv						install
insserv						install
libacl1						install
libattr1					install
libbz2-1.0					install
libc-bin					install
libc6						install
libdb4.8					install
libgcc1						install
liblocale-gettext-perl				install
liblzma2					install
libncurses5					install
libpam-modules					install
libpam-runtime					install
libpam0g					install
libreadline6					install
libselinux1					install
libstdc++6					install
libtext-charwidth-perl				install
libtext-iconv-perl				install
libtext-wrapi18n-perl				install
libusb-0.1-4					install
mawk						install
passwd						install
perl-base					install
readline-common					install
sed						install
sensible-utils					install
xz-utils					install
zlib1g						install

setup.sh

#!/bin/sh

set -e -x

# pass path to the root. Don't let it run without one as it will break your system
if [ "" = "$1" ] ; then 
	echo "You need to specify a path to the target rootfs"
else
	if [ -e "$1" ] ; then
		ROOTFS="$1"
	else 
		echo "Root dir $ROOTFS not found"
	fi
fi

if [ "/" = "ROOTFS" ] ; then echo "Refusing to change your build system's files" ; fi

# set hostname
echo botbrew > $ROOTFS/etc/hostname
echo "127.0.0.1 localhost.localdomain localhost" > ${ROOTFS}/etc/hosts
echo "127.0.1.1 botbrew botbrew" >> ${ROOTFS}/etc/hosts
echo "nameserver 8.8.8.8" > ${ROOTFS}/etc/resolv.conf
echo "nameserver 8.8.4.4" >> ${ROOTFS}/etc/resolv.conf
cp /usr/bin/qemu-arm-static ${ROOTFS}/usr/bin/
cp selections ${ROOTFS}/
cp init.sh ${ROOTFS}/

strnstr.c

/*-
 * Copyright (c) 2001 Mike Barcroft <[email protected]>
 * Copyright (c) 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Chris Torek.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)strstr.c	8.1 (Berkeley) 6/4/93";
#endif /* LIBC_SCCS and not lint */
#include <sys/cdefs.h>
__FBSDID("$FreeBSD: src/lib/libc/string/strnstr.c,v 1.2.2.1 2001/12/09 06:50:03 mike Exp $");

#include <string.h>

/*
 * Find the first occurrence of find in s, where the search is limited to the
 * first slen characters of s.
 */
char *
strnstr(s, find, slen)
	const char *s;
	const char *find;
	size_t slen;
{
	char c, sc;
	size_t len;

	if ((c = *find++) != '\0') {
		len = strlen(find);
		do {
			do {
				if ((sc = *s++) == '\0' || slen-- < 1)
					return (NULL);
			} while (sc != c);
			if (len > slen)
				return (NULL);
		} while (strncmp(s, find, len) != 0);
		s--;
	}
	return ((char *)s);
}

strnstr.h

#ifndef STRNSTR_H
#define STRNSTR_H

char *strnstr(const char *s, const char *find, size_t slen);

#endif