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Fix run-as which was broken in Android 4.3

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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

(cherry picked from commit f2904a7b63)

Change-Id: I0f6cb9efd49f5c2c491f7aa1d614d700a5ec2304
This commit is contained in:
Alex Klyubin 2013-08-05 13:03:58 -07:00
parent 821678e1c7
commit b0739c662d
1 changed files with 24 additions and 19 deletions
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43
run-as/run-as.c
View file

@ -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 @@ int main(int argc, char **argv)
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 @@ int main(int argc, char **argv)
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) {