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/*
**
** Copyright 2010, The Android Open Source Project
**
** Licensed under the Apache License, Version 2.0 (the "License");
** you may not use this file except in compliance with the License.
** You may obtain a copy of the License at
**
** http://www.apache.org/licenses/LICENSE-2.0
**
** Unless required by applicable law or agreed to in writing, software
** distributed under the License is distributed on an "AS IS" BASIS,
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
** See the License for the specific language governing permissions and
** limitations under the License.
*/
#define PROGNAME "run-as"
#define LOG_TAG PROGNAME
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <dirent.h>
#include <errno.h>
#include <unistd.h>
#include <time.h>
#include <stdarg.h>
#include <selinux/android.h>
#include <private/android_filesystem_config.h>
#include "package.h"
/*
* WARNING WARNING WARNING WARNING
*
* This program runs with CAP_SETUID and CAP_SETGID capabilities on Android
* production devices. Be very conservative when modifying it to avoid any
* serious security issue. Keep in mind the following:
*
* - This program should only run for the 'root' or 'shell' users
*
* - Avoid anything that is more complex than simple system calls
* until the uid/gid has been dropped to that of a normal user
* or you are sure to exit.
*
* This avoids depending on environment variables, system properties
* and other external factors that may affect the C library in
* unpredictable ways.
*
* - Do not trust user input and/or the filesystem whenever possible.
*
* Read README.TXT for more details.
*
*
*
* The purpose of this program is to run a command as a specific
* application user-id. Typical usage is:
*
* run-as <package-name> <command> <args>
*
* The 'run-as' binary is installed with CAP_SETUID and CAP_SETGID file
* capabilities, but will check the following:
*
* - that it is invoked from the 'shell' or 'root' user (abort otherwise)
* - that '<package-name>' is the name of an installed and debuggable package
* - that the package's data directory is well-formed (see package.c)
*
* If so, it will drop to the application's user id / group id, cd to the
* package's data directory, then run the command there.
*
* NOTE: In the future it might not be possible to cd to the package's data
* directory under that package's user id / group id, in which case this
* utility will need to be changed accordingly.
*
* This can be useful for a number of different things on production devices:
*
* - Allow application developers to look at their own applicative data
* during development.
*
* - Run the 'gdbserver' binary executable to allow native debugging
*/
static void
usage(void)
{
const char* str = "Usage: " PROGNAME " <package-name> <command> [<args>]\n\n";
write(1, str, strlen(str));
exit(1);
}
static void
panic(const char* format, ...)
{
va_list args;
fprintf(stderr, "%s: ", PROGNAME);
va_start(args, format);
vfprintf(stderr, format, args);
va_end(args);
exit(1);
}
int main(int argc, char **argv)
{
const char* pkgname;
int myuid, uid, gid;
PackageInfo info;
/* check arguments */
if (argc < 2)
usage();
/* check userid of caller - must be 'shell' or 'root' */
myuid = getuid();
if (myuid != AID_SHELL && myuid != AID_ROOT) {
panic("only 'shell' or 'root' users can run this program\n");
}
/* retrieve package information from system */
pkgname = argv[1];
if (get_package_info(pkgname, &info) < 0) {
panic("Package '%s' is unknown\n", pkgname);
return 1;
}
/* reject system packages */
if (info.uid < AID_APP) {
panic("Package '%s' is not an application\n", pkgname);
return 1;
}
/* reject any non-debuggable package */
if (!info.isDebuggable) {
panic("Package '%s' is not debuggable\n", pkgname);
return 1;
}
/* check that the data directory path is valid */
if (check_data_path(info.dataDir, info.uid) < 0) {
panic("Package '%s' has corrupt installation\n", pkgname);
return 1;
}
/* Ensure that we change all real/effective/saved IDs at the
* same time to avoid nasty surprises.
*/
uid = gid = info.uid;
if(setresgid(gid,gid,gid) || setresuid(uid,uid,uid)) {
panic("Permission denied\n");
return 1;
}
if (selinux_android_setcontext(uid, 0, info.seinfo, pkgname) < 0) {
panic("Could not set SELinux security context: %s\n", strerror(errno));
return 1;
}
/* cd into the data directory */
{
int ret;
do {
ret = chdir(info.dataDir);
} while (ret < 0 && errno == EINTR);
if (ret < 0) {
panic("Could not cd to package's data directory: %s\n", strerror(errno));
return 1;
}
}
/* User specified command for exec. */
if (argc >= 3 ) {
if (execvp(argv[2], argv+2) < 0) {
panic("exec failed for %s Error:%s\n", argv[2], strerror(errno));
return -errno;
}
}
/* Default exec shell. */
execlp("/system/bin/sh", "sh", NULL);
panic("exec failed\n");
return 1;
}
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