/*
**
** 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 <stdio.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.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"
/* 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.
* Returns a pointer into the src string, leaving off where the copy
* has stopped. The copy will stop when dstlen, srclen or a null
* character on src has been reached.
*/
static const char*
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 src;
dstend--; /* make room for terminating zero */
while (dst < dstend && src < srcend && *src != '\0')
*dst++ = *src++;
*dst = '\0'; /* zero-terminate result */
return src;
}
/* Open 'filename' and map it into our address-space.
* Returns buffer address, or NULL on error
* On exit, *filesize will be set to the file's size, or 0 on error
*/
static void*
map_file(const char* filename, size_t* filesize)
{
int fd, ret, old_errno;
struct stat st;
size_t length = 0;
void* address = NULL;
gid_t oldegid;
*filesize = 0;
/*
* Temporarily switch effective GID to allow us to read
* the packages file
*/
oldegid = getegid();
if (setegid(AID_PACKAGE_INFO) < 0) {
return NULL;
}
/* open the file for reading */
fd = TEMP_FAILURE_RETRY(open(filename, O_RDONLY));
if (fd < 0) {
return NULL;
}
/* restore back to our old egid */
if (setegid(oldegid) < 0) {
goto EXIT;
}
/* get its size */
ret = TEMP_FAILURE_RETRY(fstat(fd, &st));
if (ret < 0)
goto EXIT;
/* Ensure that the file is owned by the system user */
if ((st.st_uid != AID_SYSTEM) || (st.st_gid != AID_PACKAGE_INFO)) {
goto EXIT;
}
/* Ensure that the file has sane permissions */
if ((st.st_mode & S_IWOTH) != 0) {
goto EXIT;
}
/* Ensure that the size is not ridiculously large */
length = (size_t)st.st_size;
if ((off_t)length != st.st_size) {
errno = ENOMEM;
goto EXIT;
}
/* Memory-map the file now */
do {
address = mmap(NULL, length, PROT_READ, MAP_PRIVATE, fd, 0);
} while (address == MAP_FAILED && errno == EINTR);
if (address == MAP_FAILED) {
address = NULL;
goto EXIT;
}
/* We're good, return size */
*filesize = length;
EXIT:
/* close the file, preserve old errno for better diagnostics */
old_errno = errno;
close(fd);
errno = old_errno;
return address;
}
/* unmap the file, but preserve errno */
static void
unmap_file(void* address, size_t size)
{
int old_errno = errno;
TEMP_FAILURE_RETRY(munmap(address, size));
errno = old_errno;
}
/* 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;
/* /data/user/0 is a known safe symlink */
if (strcmp("/data/user/0", path) == 0)
return 0;
/* 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;
}
/* 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, uid_t userId, PackageInfo *info)
{
char* buffer;
size_t buffer_len;
const char* p;
const char* buffer_end;
int result = -1;
info->uid = 0;
info->isDebuggable = 0;
info->dataDir[0] = '\0';
info->seinfo[0] = '\0';
buffer = map_file(PACKAGES_LIST_FILE, &buffer_len);
if (buffer == NULL)
return -1;
p = buffer;
buffer_end = buffer + buffer_len;
/* expect the following format on each line of the control file:
*
* <pkgName> <uid> <debugFlag> <dataDir> <seinfo>
*
* 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)
* <seinfo> is the seinfo label associated with the package
*
* 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;
/* If userId == 0 (i.e. user is device owner) we can use dataDir value
* from packages.list, otherwise compose data directory as
* /data/user/$uid/$packageId
*/
if (userId == 0) {
p = string_copy(info->dataDir, sizeof info->dataDir, p, q - p);
} else {
snprintf(info->dataDir,
sizeof info->dataDir,
"/data/user/%d/%s",
userId,
pkgName);
p = q;
}
/* skip spaces */
if (parse_spaces(&p, end) < 0)
goto BAD_FORMAT;
/* fifth field is the seinfo string */
q = skip_non_spaces(p, end);
if (q == p)
goto BAD_FORMAT;
string_copy(info->seinfo, sizeof info->seinfo, p, q - p);
/* Ignore the rest */
result = 0;
goto EXIT;
NEXT_LINE:
p = next;
}
/* the package is unknown */
errno = ENOENT;
result = -1;
goto EXIT;
BAD_FORMAT:
errno = EINVAL;
result = -1;
EXIT:
unmap_file(buffer, buffer_len);
return result;
}