Bővebben a 2.2, 2.4, 2.6 kerneleket érintő hibáról

Marcelo Tosatti ma sebtében két kernel release-t is kiadott. Az egyik a 2.4.24-rc1 volt, majd néhány perccel később a 2.4.24-rc1-et kiadta változatlanul stabil 2.4.24-ként. Ennek az oka az, hogy olyan biztonsági hibát találtak a 2.2, 2.4 és 2.6 kernel kódjában, amelyet kihasználva root jogokhoz juthat a rosszindulatú támadó.

Van proof of concept exploit, és működik is. Kötelező olvasmány (hiba leírása) ->Synopsis: Linux kernel do_mremap local privilege escalation vulnerability

Product: Linux kernel

Version: 2.2, 2.4 and 2.6 series

Vendor: http://www.kernel.org/

URL: http://isec.pl/vulnerabilities/isec-0013-mremap.txt

CVE: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0985

Author: Paul Starzetz ,

Wojciech Purczynski

Date: January 5, 2004

Issue:

======

A critical security vulnerability has been found in the Linux kernel

memory management code in mremap(2) system call due to incorrect bound

checks.

Details:

========

The mremap system call provides functionality of resizing (shrinking or

growing) as well as moving across process's addressable space of existing

virtual memory areas (VMAs) or any of its parts.

A typical VMA covers at least one memory page (which is exactly 4kB on

the i386 architecture). An incorrect bound check discovered inside the

do_mremap() kernel code performing remapping of a virtual memory area

may lead to creation of a virtual memory area of 0 bytes length.

The problem bases on the general mremap flaw that remapping of 2 pages

from inside a VMA creates a memory hole of only one page in length but

an additional VMA of two pages. In the case of a zero sized remapping

request no VMA hole is created but an additional VMA descriptor of 0

bytes in length is created.

Such a malicious virtual memory area may disrupt the operation of other

parts of the kernel memory management subroutines finally leading to

unexpected behavior.

A typical process's memory layout showing invalid VMA created with

mremap system call:

08048000-0804c000 r-xp 00000000 03:05 959142 /tmp/test

0804c000-0804d000 rw-p 00003000 03:05 959142 /tmp/test

0804d000-0804e000 rwxp 00000000 00:00 0

40000000-40014000 r-xp 00000000 03:05 1544523 /lib/ld-2.3.2.so

40014000-40015000 rw-p 00013000 03:05 1544523 /lib/ld-2.3.2.so

40015000-40016000 rw-p 00000000 00:00 0

4002c000-40158000 r-xp 00000000 03:05 1544529 /lib/libc.so.6

40158000-4015d000 rw-p 0012b000 03:05 1544529 /lib/libc.so.6

4015d000-4015f000 rw-p 00000000 00:00 0

[*] 60000000-60000000 rwxp 00000000 00:00 0

bfffe000-c0000000 rwxp fffff000 00:00 0

The broken VMA in the above example has been marked with a [*].

Impact:

=======

Since no special privileges are required to use the mremap(2) system

call any process may misuse its unexpected behavior to disrupt the kernel

memory management subsystem. Proper exploitation of this vulnerability may

lead to local privilege escalation including execution of arbitrary code

with kernel level access. Proof-of-concept exploit code has been created

and successfully tested giving UID 0 shell on vulnerable systems.

The exploitability of the discovered vulnerability is possible, although

not a trivial one. We have identified at least two different attack

vectors for the 2.4 kernel series. All users are encouraged to patch all

vulnerable systems as soon as appropriate vendor patches are released.

Credits:

========

Paul Starzetz has identified the vulnerability and

performed further research.

Disclaimer:

===========

This document and all the information it contains are provided "as is",

for educational purposes only, without warranty of any kind, whether

express or implied.

The authors reserve the right not to be responsible for the topicality,

correctness, completeness or quality of the information provided in

this document. Liability claims regarding damage caused by the use of

any information provided, including any kind of information which is

incomplete or incorrect, will therefore be rejected.