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Add 'run-as' command implementation as set-uid program.

Browse source 
Typical usage is 'run-as <package-name> <command>' to run <command>
in the data directory, and the user id, of <package-name> if, and only
if <package-name> is the name of an installed and debuggable application.

This relies on the /data/system/packages.list file generated by the
PackageManager service.

BEWARE: This is intended to be available on production devices !
This commit is contained in:
David 'Digit' Turner 2010-03-02 18:05:23 -08:00
parent 5fc070be85
commit 1f4d95296a
6 changed files with 896 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

5
include/private/android_filesystem_config.h
View file

@ -169,7 +169,7 @@ static struct fs_path_config android_files[] = {
* Do not change. */
{ 02755, AID_ROOT, AID_NET_RAW, "system/bin/ping" },
{ 02750, AID_ROOT, AID_INET, "system/bin/netcfg" },
/* the following four files are INTENTIONALLY set-uid, but they
/* the following five files are INTENTIONALLY set-uid, but they
* are NOT included on user builds. */
{ 06755, AID_ROOT, AID_ROOT, "system/xbin/su" },
{ 06755, AID_ROOT, AID_ROOT, "system/xbin/librank" },
@ -177,6 +177,9 @@ static struct fs_path_config android_files[] = {
{ 06755, AID_ROOT, AID_ROOT, "system/xbin/procmem" },
{ 06755, AID_ROOT, AID_ROOT, "system/xbin/tcpdump" },
{ 04770, AID_ROOT, AID_RADIO, "system/bin/pppd-ril" },
/* the following file is INTENTIONALLY set-uid, and IS included
* in user builds. */
{ 06750, AID_ROOT, AID_SHELL, "system/bin/run-as" },
{ 00755, AID_ROOT, AID_SHELL, "system/bin/*" },
{ 00755, AID_ROOT, AID_SHELL, "system/xbin/*" },
{ 00750, AID_ROOT, AID_SHELL, "sbin/*" },

12
run-as/Android.mk Normal file
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@ -0,0 +1,12 @@
LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
LOCAL_SRC_FILES:= run-as.c package.c
LOCAL_MODULE:= run-as
LOCAL_FORCE_STATIC_EXECUTABLE := true
LOCAL_STATIC_LIBRARIES := libc
include $(BUILD_EXECUTABLE)

190
run-as/NOTICE Normal file
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@ -0,0 +1,190 @@
Copyright (c) 2005-2008, 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.
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.
Apache License
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http://www.apache.org/licenses/
TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
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"Work" shall mean the work of authorship, whether in Source or
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"Contribution" shall mean any work of authorship, including
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institute patent litigation against any entity (including a
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471
run-as/package.c Normal file
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@ -0,0 +1,471 @@
/*
**
** 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.
*/
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <private/android_filesystem_config.h>
#include "package.h"
/*
* WARNING WARNING WARNING WARNING
*
* The following code runs as root on production devices, before
* the run-as command has dropped the uid/gid. Hence be very
* conservative and keep in mind the following:
*
* - Performance does not matter here, clarity and safety of the code
* does however. Documentation is a must.
*
* - Avoid calling C library functions with complex implementations
* like malloc() and printf(). You want to depend on simple system
* calls instead, which behaviour is not going to be altered in
* unpredictible ways by environment variables or system properties.
*
* - Do not trust user input and/or the filesystem whenever possible.
*
*/
/* The file containing the list of installed packages on the system */
#define PACKAGES_LIST_FILE "/data/system/packages.list"
/* This should be large enough to hold the content of the package database file */
#define PACKAGES_LIST_BUFFER_SIZE 8192
/* Copy 'srclen' string bytes from 'src' into buffer 'dst' of size 'dstlen'
* This function always zero-terminate the destination buffer unless
* 'dstlen' is 0, even in case of overflow.
*/
static void
string_copy(char* dst, size_t dstlen, const char* src, size_t srclen)
{
const char* srcend = src + srclen;
const char* dstend = dst + dstlen;
if (dstlen == 0)
return;
dstend--; /* make room for terminating zero */
while (dst < dstend && src < srcend && *src != '\0')
*dst++ = *src++;
*dst = '\0'; /* zero-terminate result */
}
/* Read up to 'buffsize' bytes into 'buff' from the file
* named 'filename'. Return byte length on success, or -1
* on error.
*/
static int
read_file(const char* filename, char* buff, size_t buffsize)
{
int fd, len, old_errno;
/* check the input buffer size */
if (buffsize >= INT_MAX) {
errno = EINVAL;
return -1;
}
/* open the file for reading */
do {
fd = open(filename, O_RDONLY);
} while (fd < 0 && errno == EINTR);
if (fd < 0)
return -1;
/* read the content */
do {
len = read(fd, buff, buffsize);
} while (len < 0 && errno == EINTR);
/* close the file, preserve old errno for better diagnostics */
old_errno = errno;
close(fd);
errno = old_errno;
return len;
}
/* Check that a given directory:
* - exists
* - is owned by a given uid/gid
* - is a real directory, not a symlink
* - isn't readable or writable by others
*
* Return 0 on success, or -1 on error.
* errno is set to EINVAL in case of failed check.
*/
static int
check_directory_ownership(const char* path, uid_t uid)
{
int ret;
struct stat st;
do {
ret = lstat(path, &st);
} while (ret < 0 && errno == EINTR);
if (ret < 0)
return -1;
/* must be a real directory, not a symlink */
if (!S_ISDIR(st.st_mode))
goto BAD;
/* must be owned by specific uid/gid */
if (st.st_uid != uid || st.st_gid != uid)
goto BAD;
/* must not be readable or writable by others */
if ((st.st_mode & (S_IROTH|S_IWOTH)) != 0)
goto BAD;
/* everything ok */
return 0;
BAD:
errno = EINVAL;
return -1;
}
/* This function is used to check the data directory path for safety.
* We check that every sub-directory is owned by the 'system' user
* and exists and is not a symlink. We also check that the full directory
* path is properly owned by the user ID.
*
* Return 0 on success, -1 on error.
*/
int
check_data_path(const char* dataPath, uid_t uid)
{
int nn;
/* the path should be absolute */
if (dataPath[0] != '/') {
errno = EINVAL;
return -1;
}
/* look for all sub-paths, we do that by finding
* directory separators in the input path and
* checking each sub-path independently
*/
for (nn = 1; dataPath[nn] != '\0'; nn++)
{
char subpath[PATH_MAX];
/* skip non-separator characters */
if (dataPath[nn] != '/')
continue;
/* handle trailing separator case */
if (dataPath[nn+1] == '\0') {
break;
}
/* found a separator, check that dataPath is not too long. */
if (nn >= (int)(sizeof subpath)) {
errno = EINVAL;
return -1;
}
/* reject any '..' subpath */
if (nn >= 3 &&
dataPath[nn-3] == '/' &&
dataPath[nn-2] == '.' &&
dataPath[nn-1] == '.') {
errno = EINVAL;
return -1;
}
/* copy to 'subpath', then check ownership */
memcpy(subpath, dataPath, nn);
subpath[nn] = '\0';
if (check_directory_ownership(subpath, AID_SYSTEM) < 0)
return -1;
}
/* All sub-paths were checked, now verify that the full data
* directory is owned by the application uid
*/
if (check_directory_ownership(dataPath, uid) < 0)
return -1;
/* all clear */
return 0;
}
/* Return TRUE iff a character is a space or tab */
static inline int
is_space(char c)
{
return (c == ' ' || c == '\t');
}
/* Skip any space or tab character from 'p' until 'end' is reached.
* Return new position.
*/
static const char*
skip_spaces(const char* p, const char* end)
{
while (p < end && is_space(*p))
p++;
return p;
}
/* Skip any non-space and non-tab character from 'p' until 'end'.
* Return new position.
*/
static const char*
skip_non_spaces(const char* p, const char* end)
{
while (p < end && !is_space(*p))
p++;
return p;
}
/* Find the first occurence of 'ch' between 'p' and 'end'
* Return its position, or 'end' if none is found.
*/
static const char*
find_first(const char* p, const char* end, char ch)
{
while (p < end && *p != ch)
p++;
return p;
}
/* Check that the non-space string starting at 'p' and eventually
* ending at 'end' equals 'name'. Return new position (after name)
* on success, or NULL on failure.
*
* This function fails is 'name' is NULL, empty or contains any space.
*/
static const char*
compare_name(const char* p, const char* end, const char* name)
{
/* 'name' must not be NULL or empty */
if (name == NULL || name[0] == '\0' || p == end)
return NULL;
/* compare characters to those in 'name', excluding spaces */
while (*name) {
/* note, we don't check for *p == '\0' since
* it will be caught in the next conditional.
*/
if (p >= end || is_space(*p))
goto BAD;
if (*p != *name)
goto BAD;
p++;
name++;
}
/* must be followed by end of line or space */
if (p < end && !is_space(*p))
goto BAD;
return p;
BAD:
return NULL;
}
/* Parse one or more whitespace characters starting from '*pp'
* until 'end' is reached. Updates '*pp' on exit.
*
* Return 0 on success, -1 on failure.
*/
static int
parse_spaces(const char** pp, const char* end)
{
const char* p = *pp;
if (p >= end || !is_space(*p)) {
errno = EINVAL;
return -1;
}
p = skip_spaces(p, end);
*pp = p;
return 0;
}
/* Parse a positive decimal number starting from '*pp' until 'end'
* is reached. Adjust '*pp' on exit. Return decimal value or -1
* in case of error.
*
* If the value is larger than INT_MAX, -1 will be returned,
* and errno set to EOVERFLOW.
*
* If '*pp' does not start with a decimal digit, -1 is returned
* and errno set to EINVAL.
*/
static int
parse_positive_decimal(const char** pp, const char* end)
{
const char* p = *pp;
int value = 0;
int overflow = 0;
if (p >= end || *p < '0' || *p > '9') {
errno = EINVAL;
return -1;
}
while (p < end) {
int ch = *p;
unsigned d = (unsigned)(ch - '0');
int val2;
if (d >= 10U) /* d is unsigned, no lower bound check */
break;
val2 = value*10 + (int)d;
if (val2 < value)
overflow = 1;
value = val2;
p++;
}
*pp = p;
if (overflow) {
errno = EOVERFLOW;
value = -1;
}
return value;
BAD:
*pp = p;
return -1;
}
/* Read the system's package database and extract information about
* 'pkgname'. Return 0 in case of success, or -1 in case of error.
*
* If the package is unknown, return -1 and set errno to ENOENT
* If the package database is corrupted, return -1 and set errno to EINVAL
*/
int
get_package_info(const char* pkgName, PackageInfo *info)
{
static char buffer[PACKAGES_LIST_BUFFER_SIZE];
int buffer_len;
const char* p;
const char* buffer_end;
int result;
info->uid = 0;
info->isDebuggable = 0;
info->dataDir[0] = '\0';
buffer_len = read_file(PACKAGES_LIST_FILE, buffer, sizeof buffer);
if (buffer_len < 0)
return -1;
p = buffer;
buffer_end = buffer + buffer_len;
/* expect the following format on each line of the control file:
*
* <pkgName> <uid> <debugFlag> <dataDir>
*
* where:
* <pkgName> is the package's name
* <uid> is the application-specific user Id (decimal)
* <debugFlag> is 1 if the package is debuggable, or 0 otherwise
* <dataDir> is the path to the package's data directory (e.g. /data/data/com.example.foo)
*
* The file is generated in com.android.server.PackageManagerService.Settings.writeLP()
*/
while (p < buffer_end) {
/* find end of current line and start of next one */
const char* end = find_first(p, buffer_end, '\n');
const char* next = (end < buffer_end) ? end + 1 : buffer_end;
const char* q;
int uid, debugFlag;
/* first field is the package name */
p = compare_name(p, end, pkgName);
if (p == NULL)
goto NEXT_LINE;
/* skip spaces */
if (parse_spaces(&p, end) < 0)
goto BAD_FORMAT;
/* second field is the pid */
uid = parse_positive_decimal(&p, end);
if (uid < 0)
return -1;
info->uid = (uid_t) uid;
/* skip spaces */
if (parse_spaces(&p, end) < 0)
goto BAD_FORMAT;
/* third field is debug flag (0 or 1) */
debugFlag = parse_positive_decimal(&p, end);
switch (debugFlag) {
case 0:
info->isDebuggable = 0;
break;
case 1:
info->isDebuggable = 1;
break;
default:
goto BAD_FORMAT;
}
/* skip spaces */
if (parse_spaces(&p, end) < 0)
goto BAD_FORMAT;
/* fourth field is data directory path and must not contain
* spaces.
*/
q = skip_non_spaces(p, end);
if (q == p)
goto BAD_FORMAT;
string_copy(info->dataDir, sizeof info->dataDir, p, q - p);
/* Ignore the rest */
return 0;
NEXT_LINE:
p = next;
}
/* the package is unknown */
errno = ENOENT;
return -1;
BAD_FORMAT:
errno = EINVAL;
return -1;
}

41
run-as/package.h Normal file
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@ -0,0 +1,41 @@
/*
**
** 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.
*/
#ifndef RUN_AS_PACKAGE_H
#define RUN_AS_PACKAGE_H
#include <limits.h>
#include <sys/types.h>
typedef enum {
PACKAGE_IS_DEBUGGABLE = 0,
PACKAGE_IS_NOT_DEBUGGABLE,
PACKAGE_IS_UNKNOWN,
} PackageStatus;
typedef struct {
uid_t uid;
char isDebuggable;
char dataDir[PATH_MAX];
} PackageInfo;
/* see documentation in package.c for these functiosn */
extern int get_package_info(const char* packageName, PackageInfo* info);
extern int check_data_path(const char* dataDir, uid_t uid);
#endif /* RUN_AS_PACKAGE_H */

178
run-as/run-as.c Normal file
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@ -0,0 +1,178 @@
/*
**
** 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 <private/android_filesystem_config.h>
#include "package.h"
/*
* WARNING WARNING WARNING WARNING
*
* This program runs as set-uid root 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
*
* - Statically link against the C library, and 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 setuid, 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 cd to the package's data directory, drop to the application's
* user id / group id then run the command there.
*
* 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;
}
/* then move to it */
{
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;
}
}
/* 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;
}
/* 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;
}