FreeBSD Security Advisory FreeBSD-SA-08:03.sendfile

From: FreeBSD Security Advisories <security-advisories_at_nospam>
Date: Thu Feb 14 2008 - 12:10:41 GMT
To: Bugtraq <bugtraq@securityfocus.com>

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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.FreeBSD.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:

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.
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.

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/sendfile.patch.asc

[FreeBSD 6.1]
# fetch http://security.FreeBSD.org/patches/SA-08:03/sendfile61.patch
# fetch http://security.FreeBSD.org/patches/SA-08:03/sendfile61.patch.asc

[FreeBSD 5.5]
# fetch http://security.FreeBSD.org/patches/SA-08:03/sendfile55.patch
# fetch http://security.FreeBSD.org/patches/SA-08:03/sendfile55.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-2008-0777

The latest revision of this advisory is available at http://security.FreeBSD.org/advisories/FreeBSD-SA-08:03.sendfile.asc -----BEGIN PGP SIGNATURE-----
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