Date: Tue, 7 Jan 2003 17:08:15 +1000 (EST) From: Keyran Bayliss <k.bayliss@qut.edu.au> To: freebsd-security@FreeBSD.ORG Subject: (AUSCERT ESB-2003.0007) Pine Digital Security Advisory - Integer overflow in FreeBSD kernel (fwd) Message-ID: <20030107170645.B75677@danger.its.dias.qut.edu.au>
next in thread | raw e-mail | index | archive | help
Havn't seen anthing about it on this list yet.... can't see a patch
on the site.... ??
K.
---------- Forwarded message ----------
Date: Tue, 07 Jan 2003 11:16:21 +1000 (EST)
From: auscert@auscert.org.au
To: auscert-subscriber@auscert.org.au
Subject: (AUSCERT ESB-2003.0007) Pine Digital Security Advisory - Integer
overflow in FreeBSD kernel
-----BEGIN PGP SIGNED MESSAGE-----
===========================================================================
AUSCERT External Security Bulletin Redistribution
ESB-2003.0007 -- Pine Digital Security Advisory
Integer overflow in FreeBSD kernel
07 January 2003
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: kernel
Vendor: Pine Digital Security
Operating System: FreeBSD
Impact: Root Compromise
Denial of Service
Access Required: Existing Account
- --------------------------BEGIN INCLUDED TEXT--------------------
- -----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
- - -----------------------------------------------------------------------------
Pine Digital Security Advisory
- - -----------------------------------------------------------------------------
Advisory ID : PINE-CERT-20030101
Authors : Joost Pol
Vendor Informed : 2002-12-30
Issue date : 2003-01-06
Application : Kernel
Version(s) : Various
Platforms : FreeBSD
Availability : http://www.pine.nl/press/pine-cert-20030101.txt
- - -----------------------------------------------------------------------------
Synopsis
While performing an audit for a customer, Pine Digital Security
found an integer overflow in the FreeBSD kernel.
Versions
FreeBSD:
RELENG_4 (aka -STABLE) : not vulnerable after 20021111
RELENG_5_0 (aka -CURRENT) : vulnerable in lseek(2) (199)
All current -RELEASE versions : vulnerable in fpathconf(2) (192)
OpenBSD/NetBSD: not vulnerable
Impact
Serious.
This integer overflow could cause a system panic, resulting in a
Denial-of-Service (DoS). Also, this could be used to escalate
privileges or cause the system to disclose (sensitive) files.
Description
Inside the FreeBSD kernel each file (socket, device or regular
file) opened is represented by a file structure (sys/file.h).
Amongst other members this structure holds a reference counter
(int f_count). This reference counter is increased by the fhold()
function and decreased by the fdrop() function. (both in sys/file.h)
For example, when a file is open(2)ed or dup(2)ed the reference
counter is increased and when the file is close(2)ed again the
reference counter is decreased. Once the reference counter reaches
zero, the file structure itself is deallocated.
Most system calls which perform (blocking) operations on a file
will issue a fhold() call to prevent the file from being closed
in the middle of an operation. Once the operation is finished the
(extra) reference will be released again by issuing a fdrop() call.
Inside the fpathconf(2) (192) system call we spotted a condition
where a call to fdrop() is missing. When issueing a fpathconf(2)
call on a socket it will return with an error condition but it
will not release the extra file reference.
Due to the missing fdrop() call inside the fpathconf(2) system
call is it possible to overflow the reference counter of the
file structure (int f_count).
FreeBSD -CURRENT suffers from the same problem in another syscall.
Exploitability
Causing a system panic and privilege escalation have been confirmed.
Exploitation of this bug will take time, depending on machine
speed and system limits this could vary between hours and days.
1. System Panic
A system panic can be caused by issuing around 2^31 calls to
fpathconf(2) with a filedescriptor which references a socket.
The reference counter (int f_count) will wrap to a negative
value and this will cause a panic in close(2).
2. Privilege Escalation
It is also possible (although more difficult) to gain root access
using this bug. One would open(2) a socket and dup(2) it. One would
then issue around 2^32 - 1 calls to fpathconf(2) causing the reference
counter to wrap to 1.
After closing the original filedescriptor the file structure will
be deallocated. At this point the dup(2)ed file descriptor is still
hanging around with a file structure pointing to unallocated memory.
The final step, which is left as an excercise for the reader, is
to have a sensitive file (like /etc/skeykeys) opened and
allocated at the previously freed location.
Once this happens the dup(2)ed file descriptor is still hanging
around providing access to this file. This could result in the
escalation of user privileges.
Disclaimer
Pine Digital Security does not release exploits.
Although the missing fdrop() call in fpathconf(2) was noticed
before by Nakamura Takayuki <tak@st.rim.or.jp> its impact
was severely underestimated.
Patches
FreeBSD CVS should be updated.
References
http://www.pine.nl/press/pine-cert-20030101.txt
file://usr/include/sys/file.h
file://usr/src/sys/kern/kern_descrip.c
file://usr/src/sys/kern/vfs_syscalls.c
- -----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.1 (SunOS)
iD8DBQE+GXVR0jbIKvNgu5MRAlEMAJ9hCd/HkUfUsVyriSXTv9YvAChfeQCgtoJo
0AlK0bqR4Qtq0YLZJxiPnFc=
=8KfX
- -----END PGP SIGNATURE-----
- --------------------------END INCLUDED TEXT--------------------
You have received this e-mail bulletin as a result of your organisation's
registration with AusCERT. The mailing list you are subscribed to is
maintained within your organisation, so if you do not wish to continue
receiving these bulletins you should contact your local IT manager. If
you do not know who that is, please send an email to auscert@auscert.org.au
and we will forward your request to the appropriate person.
This security bulletin is provided as a service to AusCERT's members. As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content. The decision to use any or all of this information is
the responsibility of each user or organisation, and should be done so in
accordance with site policies and procedures.
NOTE: This is only the original release of the security bulletin. It may
not be updated when updates to the original are made. If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the author's website to ensure that the information is still current.
Contact information for the authors of the original document is included
in the Security Bulletin above. If you have any questions or need further
information, please contact them directly.
Previous advisories and external security bulletins can be retrieved from:
http://www.auscert.org.au/render.html?cid=1980
If you believe that your system has been compromised, contact AusCERT or
your representative in FIRST (Forum of Incident Response and Security
Teams).
Internet Email: auscert@auscert.org.au
Facsimile: (07) 3365 7031
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
AusCERT personnel answer during Queensland business
hours which are GMT+10:00 (AEST). On call after hours
for member emergencies only.
-----BEGIN PGP SIGNATURE-----
Version: 2.6.3i
Charset: noconv
Comment: http://www.auscert.org.au/render.html?it=1967
iQCVAwUBPhqu7Ch9+71yA2DNAQHXKgP/eaCn13hYy348VjR+bFlFIecxvSFSnC2m
up0fom96MkKt1U3pxNKt8Nnt9kk3PKGpCAmoHipQRJ+hV0P9w7IrFWIhv1RSf15l
lSSeU4KQxor7zn6j1xPj25Tmtlov1xAFj8LsLrnbYYM8fMG3YoA0TNYI1VAMVDBU
WDWAghBU0nI=
=2UKi
-----END PGP SIGNATURE-----
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-security" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20030107170645.B75677>