Date: Tue, 11 May 1999 12:55:40 -0700 (PDT) From: Thamer Al-Herbish <shadows@whitefang.com> To: freebsd-security@FreeBSD.ORG Subject: Wrapping syscalls Message-ID: <Pine.BSF.4.05.9905111251500.253-100000@rage.whitefang.com>
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I've recently had the idea of wrapping system calls with a capability check per process. The end objective is to have a patch for FreeBSD that adds a system call which can be used to drop the capability of calling a certain system call. The simplest example would be a web server that after chroot()ing would call lsyscall(EXECVE) and drop its ability to execve(). It may also drop its write() ability and so on. Leaving only a few read-only system calls that would effectively make it read-only. Has anyone attempted something similar? Is there an inherent effeciency problem with just adding checks to the beginning of every system call? I'm aware of some security issues that are _not_ solved by this: specificially dropping write() capabilities but still being able to truncate files with the open() call. Additionally, the child process will inheret its parent's disposition and never be able to reclaim a system call. -- Thamer Al-Herbish PGP public key: shadows@whitefang.com http://www.whitefang.com/pgpkey.txt [ The Secure UNIX Programming FAQ http://www.whitefang.com/sup/ ] To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-security" in the body of the message
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