Add 'run-as' command implementation as set-uid program.
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 !
diff --git a/run-as/package.c b/run-as/package.c
new file mode 100644
index 0000000..46f8239
--- /dev/null
+++ b/run-as/package.c
@@ -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;
+}