executing insmod hangs the entire os

[Valdis.Kletnieks at vt.edu]

On Tue, 17 Feb 2015 21:46:00 +0530, noyb noybee said:

> am on a VM running CentOS 6.6 with kernel version 2.6.32-504.

Which probably has kernel relocation and ASLR enabled.

> unsigned long *syscall_table = (unsigned long *)0xffffffff81600560;

So that isn't pointing at the syscall table in the running kernel.

>     syscall_table[__NR_chroot] = new_chroot;

So you just trashed an essentially random location in memory.

You explained in a private email what you were trying to do here - and
I'll point out that it essentially changes the kernel API in unexpected
and undocumented ways.  It even introduces some security holes and bugs (hint -
if you close all file descriptors, what happens to programs that were expecting
stdin/stdout/stderr to be open?  In particular, programs that open, say,
/dev/log so they have syslog output, and then chroot.  Or programs that
open a socket, then chroot and drop permissions (like openssh's sshd for
privilege separation).

You're really not doing yourself a favor with this whack-a-mole approach
to security.  You *really* need to sit down and think about what problem
you're trying to solve here.


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