Fix run-as which was broken in Android 4.3
In Android 4.3 the run-as binary no longer has the SUID/SGID bits
set. Instead, it requires to be installed with setuid and setgid
file-based capabilities. As a result of the above two changes, the
binary no longer executes as root when invoked by the "shell" user
but can still change its UID/GID to that of the target package.
Unfortunately, run-as attempts to chdir into the target package's
data directory before changing its effective UID/GID. As a result,
when run-as is invoked by the "shell" user, the chdir operation
fails.
The fix is for run-as to chdir after changing the effective UID/GID
to those of the target package.
Bug: 10154652
Change-Id: I48ecfeab7cd36991968d49e2382ceb4110694709
diff --git a/run-as/run-as.c b/run-as/run-as.c
index 3c0ecc4..cc05e63 100644
--- a/run-as/run-as.c
+++ b/run-as/run-as.c
@@ -36,9 +36,9 @@
/*
* 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 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
*
@@ -61,14 +61,19 @@
*
* run-as <package-name> <command> <args>
*
- * The 'run-as' binary is setuid, but will check the following:
+ * 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 cd to the package's data directory, drop to the application's
- * user id / group id then run the command there.
+ * 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:
*
@@ -141,19 +146,6 @@
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.
*/
@@ -168,6 +160,19 @@
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) {