Security

Secure processes have some restrictions applied to the evaluation of their dependencies and runpaths to prevent malicious dependency substitution or symbol interposition.

The runtime linker categorizes a process as secure if the user is not a superuser, and either the real user and effective user identifiers are not equal, or the real group and effective group identifiers are not equal. See the getuid(2), geteuid(2), getgid(2) and getegid(2) man pages.

The default trusted directory known to the runtime linker is /usr/lib/secure for 32–bit objects or /usr/lib/secure/64 for 64–bit objects. The utility crle(1) may be used to specify additional trusted directories applicable for secure applications. Administrators who use this technique should ensure that the target directories are suitably protected from malicious intrusion.

If an LD_LIBRARY_PATH family environment variable is in effect for a secure process, then only the trusted directories specified by this variable will be used to augment the runtime linker's search rules. See “Directories Searched by the Runtime Linker”.

In a secure process, any runpath specifications provided by the application or any of its dependencies are used, provided the runpaths are full path names (that is, the path name starts with a `/').

In a secure process, the expansion of the $ORIGIN string is allowed only if it expands to a trusted directory. See “Security”.

In a secure process, LD_SIGNAL is ignored.

Additional objects can be loaded with a secure process using the LD_PRELOAD or LD_AUDIT environment variables. These objects must be specified as full path names or simple file names. Full path names are restricted to known trusted directories. Simple file names, in which no `/' appears in the name, are located subject to the search path restrictions previously described. These files resolve only to known trusted directories.

In a secure process, any dependencies that consist of simple file names are processed using the path name restrictions previously described. Dependencies that are expressed as full or relative path names will be used as provided. Therefore, the developer of a secure process should ensure that the target directory referenced as a full or relative path name dependency is suitably protected from malicious intrusion.

When creating a secure process, do not use relative path names to express dependencies or to construct dlopen(3DL) path names. This restriction should be applied to the application and to all dependencies.