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FreeBSD-SA-08:03.sendfile
Security Advisory
The FreeBSD Project
Topic: sendfile(2) write-only file permission
bypass
Category: core
Module: sys_kern
Announced: 2008-02-14
Credits: Kostik Belousov
Affects: All supported versions of FreeBSD
Corrected: 2008-02-14 11:45:00 UTC (RELENG_7,
7.0-PRERELEASE)
2008-02-14 11:45:41 UTC (RELENG_7_0,
7.0-RELEASE)
2008-02-14 11:46:08 UTC (RELENG_6,
6.3-STABLE)
2008-02-14 11:46:41 UTC (RELENG_6_3,
6.3-RELEASE-p1)
2008-02-14 11:47:06 UTC (RELENG_6_2,
6.2-RELEASE-p11)
2008-02-14 11:47:39 UTC (RELENG_6_1,
6.1-RELEASE-p23)
2008-02-14 11:49:39 UTC (RELENG_5,
5.5-STABLE)
2008-02-14 11:50:28 UTC (RELENG_5_5,
5.5-RELEASE-p19)
CVE Name: CVE-2008-0777
For general information regarding FreeBSD Security
Advisories,
including descriptions of the fields above, security
branches, and the
following sections, please visit <URL:http://security.Fre
eBSD.org/>.
I. Background
The sendfile(2) system call allows a server application
(such as a
HTTP or FTP server) to transmit the contents of a file over
a network
connection without first copying it to application memory.
High
performance servers such as the Apache HTTP Server and ftpd
use sendfile.
II. Problem Description
When a process opens a file (and other file system objects,
such as
directories), it specifies access flags indicating its
intent to read,
write, or perform other operations. These flags are checked
against
file system permissions, and then stored in the resulting
file
descriptor to validate future operations against.
The sendfile(2) system call does not check the file
descriptor access
flags before sending data from a file.
III. Impact
If a file is write-only, a user process can open the file
and use
sendfile to send the content of the file over a socket, even
though the
user does not have read access to the file, resulting in
possible
disclosure of sensitive information.
IV. Workaround
No workaround is available, but systems are only vulnerable
if
write-only files exist, which are not widely used.
V. Solution
Perform one of the following:
1) Upgrade your vulnerable system to 5-STABLE, 6-STABLE, or
7.0-PRERELEASE, or to the RELENG_7_0, RELENG_6_3,
RELENG_6_2,
RELENG_6_1, or RELENG_5_5 security branch dated after the
correction
date.
2) To patch your present system:
The following patches have been verified to apply to FreeBSD
5.5, 6.1,
6.2, 6.3, and 7.0 systems.
a) Download the relevant patch from the location below, and
verify the
detached PGP signature using your PGP utility.
[FreeBSD 6.2, 6.3, and 7.0]
# fetch http://security.FreeBSD.org/patches/SA-08:03/sendfile
.patch
# fetch http://security.FreeBSD.org/patches/SA-08:03/send
file.patch.asc
[FreeBSD 6.1]
# fetch http://security.FreeBSD.org/patches/SA-08:03/sendfi
le61.patch
# fetch http://security.FreeBSD.org/patches/SA-08:03/se
ndfile61.patch.asc
[FreeBSD 5.5]
# fetch http://security.FreeBSD.org/patches/SA-08:03/sendfi
le55.patch
# fetch http://security.FreeBSD.org/patches/SA-08:03/se
ndfile55.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
-
------------------------------------------------------------
-------------
RELENG_5
src/sys/kern/kern_descrip.c
1.243.2.11
RELENG_5_5
src/UPDATING
1.342.2.35.2.20
src/sys/conf/newvers.sh
1.62.2.21.2.21
src/sys/kern/kern_descrip.c
1.243.2.9.2.1
RELENG_6
src/sys/kern/kern_descrip.c
1.279.2.16
src/sys/kern/uipc_syscalls.c
1.221.2.5
RELENG_6_3
src/UPDATING
1.416.2.37.2.5
src/sys/conf/newvers.sh
1.69.2.15.2.4
src/sys/kern/kern_descrip.c
1.279.2.15.2.1
src/sys/kern/uipc_syscalls.c
1.221.2.4.4.1
RELENG_6_2
src/UPDATING
1.416.2.29.2.15
src/sys/conf/newvers.sh
1.69.2.13.2.14
src/sys/kern/kern_descrip.c
1.279.2.9.2.1
src/sys/kern/uipc_syscalls.c
1.221.2.4.2.1
RELENG_6_1
src/UPDATING
1.416.2.22.2.26
src/sys/conf/newvers.sh
1.69.2.11.2.25
src/sys/kern/kern_descrip.c
1.279.2.6.2.1
src/sys/kern/uipc_syscalls.c
1.221.2.1.2.1
RELENG_7
src/sys/kern/kern_descrip.c
1.313.2.1
src/sys/kern/uipc_syscalls.c
1.259.2.2
RELENG_7_0
src/UPDATING
1.507.2.3.2.3
src/sys/kern/kern_descrip.c
1.313.4.1
src/sys/kern/uipc_syscalls.c
1.259.4.2
-
------------------------------------------------------------
-------------
VII. References
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-200
8-0777
The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeB
SD-SA-08:03.sendfile.asc
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