When we work with hardened kernels and tools like grsecurity and PaX, we face problems like:
- The kernel kills applications.
- Some applications can not start.
- We can't compile applications.
- And many others.....
This problem depends on the security level configured in the kernel. We need to configure and tell the system that some blocked applications are reliable and trusted, this is because some legitimate applications will attempt to generate code at run time which is executed out of memory. PaX does not allow this and will promptly kill the offending application.
The most notable of these applications are XFree/Xorg, mplayer, and multimedia tools based on xine-lib and Java virtual machine.
homero / # java -version Killedhomero / # uname -a Linux homero 2.6.27.15-grsec-2.1.12-vs2.3.0.36.4 #11 SMP Fri Mar 25 17:30:38 CST 2011 i686 Intel(R) Xeon(TM) CPU 3.20GHz GenuineIntel GNU/Linuxhomero ~ # tail -f /var/log/pax.log Aug 8 13:06:23 homero kernel: [7748633.853670] PAX: From X.X.X.X: execution attempt in:, 48f7f000-48fa7000 48f7f000 Aug 8 13:06:23 homero kernel: [7748633.853683] PAX: terminating task: /usr/local/jdk1.6.0_26/bin/java(java):18549, uid/euid: 0/0, PC: 48f7f040, SP: 4b05dddc Aug 8 13:06:23 homero kernel: [7748633.853695] PAX: bytes at PC: f0 83 04 24 00 8b 44 24 0c c3 00 00 00 00 00 00 00 00 00 00 Aug 8 13:06:23 homero kernel: [7748633.853718] PAX: bytes at SP-4: homero bin # pwd /usr/local/jdk1.6.0_26/bin
To solve this problem we need to work with some PaX utils and applications, such as paxctl and chpax, in order to change the rules of security but only with some applications.
homero bin # emerge pax-utils pax paxctl paxtest -pv These are the packages that would be merged, in order: Calculating dependencies... done! [ebuild R ] sys-apps/paxctl-0.5 0 kB [ebuild R ] app-misc/pax-utils-0.2.2 USE="caps" 0 kB [ebuild R ] app-arch/pax-3.3.4 0 kB [ebuild R ~] app-admin/paxtest-0.9.9-r2 0 kB Total: 4 packages (4 reinstalls), Size of downloads: 0 kB * IMPORTANT: 4 news items need reading for repository 'gentoo'. * Use eselect news to read news items.
First, we need to create the PT_PAX_FLAGS
homero bin # paxctl -C * file ControlPanel is not a valid ELF executable file HtmlConverter is not a valid ELF executable file appletviewer got a new PT_PAX_FLAGS program header file apt got a new PT_PAX_FLAGS program header file extcheck got a new PT_PAX_FLAGS program header file idlj got a new PT_PAX_FLAGS program header file jar got a new PT_PAX_FLAGS program header file jarsigner got a new PT_PAX_FLAGS program header file java got a new PT_PAX_FLAGS program header file java-rmi.cgi is not a valid ELF executable file javac got a new PT_PAX_FLAGS program header file javadoc got a new PT_PAX_FLAGS program header file javah got a new PT_PAX_FLAGS program header file javap got a new PT_PAX_FLAGS program header file javaws got a new PT_PAX_FLAGS program header file jconsole got a new PT_PAX_FLAGS program header file jcontrol is not a valid ELF executable file jdb got a new PT_PAX_FLAGS program header file jhat got a new PT_PAX_FLAGS program header file jinfo got a new PT_PAX_FLAGS program header file jmap got a new PT_PAX_FLAGS program header file jps got a new PT_PAX_FLAGS program header file jrunscript got a new PT_PAX_FLAGS program header file jsadebugd got a new PT_PAX_FLAGS program header file jstack got a new PT_PAX_FLAGS program header file jstat got a new PT_PAX_FLAGS program header file jstatd got a new PT_PAX_FLAGS program header file jvisualvm is not a valid ELF executable file keytool got a new PT_PAX_FLAGS program header file native2ascii got a new PT_PAX_FLAGS program header file orbd got a new PT_PAX_FLAGS program header file pack200 got a new PT_PAX_FLAGS program header file policytool got a new PT_PAX_FLAGS program header file rmic got a new PT_PAX_FLAGS program header file rmid got a new PT_PAX_FLAGS program header file rmiregistry got a new PT_PAX_FLAGS program header file schemagen got a new PT_PAX_FLAGS program header file serialver got a new PT_PAX_FLAGS program header file servertool got a new PT_PAX_FLAGS program header file tnameserv got a new PT_PAX_FLAGS program header file unpack200 got a new PT_PAX_FLAGS program header file wsgen got a new PT_PAX_FLAGS program header file wsimport got a new PT_PAX_FLAGS program header file xjc got a new PT_PAX_FLAGS program headerhomero bin # paxctl -v java PaX control v0.5 Copyright 2004,2005,2006,2007 PaX Team- PaX flags: -------x-e-- [java] RANDEXEC is disabled EMUTRAMP is disabled
The problem is the mprotect flag, because it is enabled.
Name
mprotect - control allowable accesses to a region of memory Synopsis #includeint mprotect(const void *addr, size_t len, int prot); Description The function mprotect() specifies the desired protection for the memory page(s) containing part or all of the interval [addr,addr+len-1]. If an access is disallowed by the protection given it, the program receives a SIGSEGV. The goal of MPROTECT is to help prevent the introduction of new executable code into the task’s address space. This is accomplished by restricting the mmap() and mprotect() interfaces. The restrictions prevent: - Creating executable anonymous mappings. - Creating executable/writable file mappings. - Making an executable/read-only file mapping writable except for performing relocations on an ET_DYN ELF file (non-PIC shared library). - Making a non-executable mapping executable.
So we need to disable it.
homero bin # paxctl -m * file ControlPanel is not a valid ELF executable file HtmlConverter is not a valid ELF executable file java-rmi.cgi is not a valid ELF executable file jcontrol is not a valid ELF executable file jvisualvm is not a valid ELF executablehomero bin # paxctl -v java PaX control v0.5 Copyright 2004,2005,2006,2007 PaX Team- PaX flags: -----m-x-e-- [java] MPROTECT is disabled RANDEXEC is disabled EMUTRAMP is disabled homero bin # java -version java version "1.6.0_26" Java(TM) SE Runtime Environment (build 1.6.0_26-b03) Java HotSpot(TM) Client VM (build 20.1-b02, mixed mode)
And now we can run any java application on our hardened system.
