Need to Know's

The difference between setuid and non-setuid (logging-only) mode

The gLExec executable is installable in two ways, with and without the setuid (file system) bit on root. With the setuid-bit enabled on root, this effectively means that gLExec is being executed with root privileges. Without the setuid or setgid bits on root the gLExec executable is like any other regular executable.

The safety features of gLExec are implemented with great care to avoid misuse and exploitation by anybody who executes it. As gLExec is typically installed with a setuid bit on root, this effectively means that anybody on the system is able to execute something with root privileges for a brief moment of time to perform the user switch.

Safety features

A couple of safety features that are build in the gLExec tool are:

• The LD_LIBRARY_PATH, LD_RUN_PATH and other LD_* environment variables are removed from the process environment by the Operating System before the first line of gLExec code is executed by a Unix and Linux system. Only the /etc/ld.so.conf{.d/}, RPATH settings and other system specific paths are used and resolved. This statement holds for any setuid or setgid executable.

• The rest of the environment is stripped off by gLExec. There are a couple of environment settings that can easily lead to a root exploit in the standard library of a Unix and Linux system. Only the GLEXEC_* environment variables are kept. There is an option in the glexec.conf file to preserve more variables, but these must be selected with great care and setup by each System Administrator on all their machines. These can not be influenced by the user.

• If the target user is authorized and when a mapping and Unix process identity switch the HOME and X509_USER_PROXY will be rewritten. Their value will contain the paths that are relevant for the target user account.

• The target user process has the Unix identity as mapped by LCMAPS. This could be from a separate set of pool accounts, or the regular set of pool accounts as given by the same user credentials from an LCG-CE or CREAM-CE. It could be a poolaccount defined locally on the machine. The only assumption that holds is that the target user account has the privileges that are appointed to them by the local site administrator.

Workarounds

To cope with the environment clean-up we've developed gLExec wrapper scripts which are capable of transporting your environment variables.

More information about them can be found on the GLExec Environment Wrap and Unwrap scripts page.