On Fri, 30 Jul 2010, Selphie Keller wrote:
Kernel module for chmod restrictions while in securelevel one or higher:
http://gist.github.com/501800 (fbsd 8.x)
Was looking at the new recent sendfile/mbuf exploit and it was using a
shellcode that calls chmod syscall to make a setuid/setgid binary. However
was thinking of ways to block the creation of suid/sgid binaries if the
machine is in a securelevel, beyond the normal things like nosuid/noexec
mount flags for /tmp.
So came up with this quick module to handle it, but the concept of
restricting the creation of suid/sgid binaries while in securelevel seems
like a good idea to be part of the base.
While I'm not convinced this approach is a good idea (the remainder of the
thread suggests some reasons why), a better way to implement the same policy
would be to use the MAC Framework's mpo_vnode_check_setmode entry point. This
would catch all the chmod variations, including ones in compatibility ABIs
such as the Linux ABI.
Robert
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