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AUSCERT External Security Bulletin Redistribution
ESB-2003.0558 -- FreeBSD-SA-03:09.signal
Insufficient range checking of signal numbers
11 August 2003
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: kernel
Publisher: FreeBSD
Operating System: FreeBSD 4-STABLE and prior
FreeBSD 4.8-RELEASE-p1 and prior
FreeBSD 5.1-RELEASE and prior
Impact: Denial of Service
Access Required: Existing Account
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FreeBSD-SA-03:09.signal Security Advisory
The FreeBSD Project
Topic: Insufficient range checking of signal numbers
Category: core
Module: sys
Announced: 2003-08-10
Affects: All releases of FreeBSD up to and including 4.8-RELEASE-p1,
5.1-RELEASE (but see `Problem Description' below)
FreeBSD 4-STABLE prior to the correction date
Corrected: 2003-08-10 23:09:28 UTC (RELENG_4)
2003-08-10 23:14:08 UTC (RELENG_5_1)
2003-08-10 23:17:48 UTC (RELENG_5_0)
2003-08-10 23:19:35 UTC (RELENG_4_8)
2003-08-10 23:20:30 UTC (RELENG_4_7)
2003-08-10 23:21:18 UTC (RELENG_4_6)
2003-08-10 23:22:19 UTC (RELENG_4_5)
2003-08-10 23:23:05 UTC (RELENG_4_4)
2003-08-10 23:23:56 UTC (RELENG_4_3)
FreeBSD only: YES
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit
<URL:http://www.freebsd.org/security/>.
I. Background
Signals are a UNIX mechanism for handling asynchronous events such as
pressing the terminal interrupt key (e.g. Ctrl-C), job control, memory
access violations, I/O completion, and many others. Each signal is
assigned a positive number. There are a number of mechanisms by which
a process may cause a signal to be sent, including using the kill(2)
system call or registering with certain device drivers.
II. Problem Description
Some mechanisms for causing a signal to be sent did not properly
validate the signal number, in some cases allowing the kernel to
attempt to deliver a negative or out-of-range signal number. Such
errors were present in the ptrace(2) system call and the `spigot'
video capture device driver.
The error in ptrace(2) was introduced in FreeBSD version 4.2-RELEASE
(4-STABLE dated Oct 26 04:34:41 2000 UTC).
The `spigot' device driver (including the error) was introduced in
FreeBSD 2.0.5. It has never been included in the kernel installed by
default, nor in the GENERIC kernel configuration. Only systems with
`device spigot' added to the kernel configuration are affected by this
instance of the error.
III. Impact
In most cases, attempted delivery of a negative or out-of-range signal
number will trigger an assertion failure and panic, thereby crashing
the system. A malicious local user could use this vulnerability
as a local denial-of-service attack.
However, in FreeBSD 5.x, the assertion code is not present if the
`INVARIANTS' kernel option is not used. In FreeBSD 5.0-RELEASE and
5.1-RELEASE, `INVARIANTS' is not enabled by default. In this
configuration, a malicious local user could use this vulnerability
to modify kernel memory, potentially leading to complete system
compromise. (FreeBSD 4.x is not vulnerable in this way.)
IV. Workaround
There is no workaround for the local denial-of-service attack.
The more severe impact, present only in FreeBSD 5.x systems, can be
avoided by uncommenting or adding the `INVARIANTS' line to your kernel
configuration:
options INVARIANTS #Enable calls of extra sanity checking
Recompile your kernel as described in
<URL:http://www.freebsd.org/handbook/kernelconfig.html>
and reboot the system.
NOTE WELL: This workaround is only for FreeBSD 5.x systems. This
workaround does not eliminate the possibility of a local
denial-of-service attack.
V. Solution
1) Upgrade your vulnerable system to 4.8-STABLE, or to any of the
RELENG_4_8 (4.8-RELEASE-p2), RELENG_4_7 (4.7-RELEASE-p12), or
RELENG_5_1 (5.1-RELEASE-p1) security branches dated after the
respective correction dates.
2) To patch your present system:
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
[FreeBSD 5.1-RELEASE]
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-03:09/signal51.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-03:09/signal51.patch.asc
[FreeBSD 5.0-RELEASE]
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-03:09/signal50.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-03:09/signal50.patch.asc
[FreeBSD 4.8-RELEASE, 4.8-STABLE, 4.7-STABLE dated Jan 2 20:39:13 2003 UTC
or later]
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-03:09/signal4s.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-03:09/signal4s.patch.asc
[FreeBSD 4.3-RELEASE through 4.7-RELEASE, 4.7-STABLE dated before
Jan 2 20:39:13 2003 UTC]
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-03:09/signal47.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-03:09/signal47.patch.asc
b) Apply the patch.
# cd /usr/src
# patch < /path/to/patch
c) Recompile your kernel as described in
<URL:http://www.freebsd.org/handbook/kernelconfig.html>
and reboot the system.
VI. Correction details
The following list contains the revision numbers of each file that was
corrected in FreeBSD.
Branch Revision
Path
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src/sys/UPDATING
RELENG_5_1 1.251.2.2
RELENG_5_0 1.229.2.15
RELENG_4_8 1.73.2.80.2.4
RELENG_4_7 1.73.2.74.2.15
RELENG_4_6 1.73.2.68.2.43
RELENG_4_5 1.73.2.50.2.45
RELENG_4_4 1.73.2.43.2.46
RELENG_4_3 1.73.2.28.2.33
src/sys/conf/newvers.sh
RELENG_5_1 1.50.2.3
RELENG_5_0 1.48.2.10
RELENG_4_8 1.44.2.29.2.3
RELENG_4_7 1.44.2.26.2.14
RELENG_4_6 1.44.2.23.2.32
RELENG_4_5 1.44.2.20.2.29
RELENG_4_4 1.44.2.17.2.37
RELENG_4_3 1.44.2.14.2.23
src/sys/i386/isa/spigot.c
RELENG_4 1.44.2.1
RELENG_5_1 1.58.2.1
RELENG_5_0 1.55.2.1
RELENG_4_8 1.44.14.1
RELENG_4_7 1.44.12.1
RELENG_4_6 1.44.10.1
RELENG_4_5 1.44.8.1
RELENG_4_4 1.44.6.1
RELENG_4_3 1.44.4.1
src/sys/kern/sys_process.c
RELENG_4 1.51.2.7
RELENG_5_1 1.108.2.1
RELENG_5_0 1.104.2.1
RELENG_4_8 1.51.2.6.2.1
RELENG_4_7 1.51.2.4.2.1
RELENG_4_6 1.51.2.3.4.1
RELENG_4_5 1.51.2.3.2.1
RELENG_4_4 1.51.2.1.4.2
RELENG_4_3 1.51.2.1.2.2
src/sys/kern_sig.c
RELENG_5_1 1.239.2.1
RELENG_5_0 1.197.2.1
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