Dynamically linked libraries are commonly used in software programs to facilitate code reuse. Once a library is linked into a software program, a bug in the library can lead to compromise of the whole program. Moreover, the library may also contain malicious code. Existing solutions for software component isolation assume simple interactions between a library and the main program, otherwise, they require significant modification of the main program and the library. In this paper, we propose a novel solution, Codejail, which supports a partial isolation of libraries that have tight memory interactions with the main program. Codejail requires no modification to the main program or the library. We demonstrate using a Linux prototype that Codejail can work easily with real-world programs and libraries. The performance is good for a portable implementation with costs commensurate with the degree of tight interaction.