Linker and Libraries Guide


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 super-user, and the real user and effective user identifiers are not equal. Similarly, if the user is not a super-user and the real group and effective group identifiers are not equal, the process is deemed secure. 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, only the trusted directories specified by this variable are 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 is used, provided it is a full pathname, that is, the pathname 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_CONFIG is ignored. A secure process uses the default configuration file, if it exists. See crle(1).

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. Simple file names 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 expressed as full or relative path names are used as is. 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.