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FreeBSD-SA-05:02.sendfile                                   Security Advisory
                                                          The FreeBSD Project

Topic:          sendfile kernel memory disclosure

Category:       core
Module:         sys_kern
Announced:      2005-04-04
Credits:        Sven Berkvens <sven@berkvens.net>
                Marc Olzheim <zlo@zlo.nu>
Affects:        All FreeBSD 4.x releases
                All FreeBSD 5.x releases prior to 5.4-RELEASE
Corrected:      2005-04-04 23:52:02 UTC (RELENG_5, 5.4-STABLE)
                2005-04-04 23:52:35 UTC (RELENG_5_4, 5.4-RELEASE)
                2005-04-04 23:53:24 UTC (RELENG_5_3, 5.3-RELEASE-p7)
                2005-04-04 23:53:36 UTC (RELENG_4, 4.11-STABLE)
                2005-04-04 23:53:56 UTC (RELENG_4_11, 4.11-RELEASE-p2)
                2005-04-04 23:54:13 UTC (RELENG_4_10, 4.10-RELEASE-p7)
                2005-04-04 23:54:33 UTC (RELENG_4_8, 4.8-RELEASE-p29)
CVE Name:       CAN-2005-0708

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

The sendfile(2) system call allows a server application (such as an 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 Apache and ftpd use sendfile.

II.  Problem Description

If the file being transmitted is truncated after the transfer has started but before it completes, sendfile(2) will transfer the contents of more or less random portions of kernel memory in lieu of the missing part of the file.

III. Impact

A local user could create a large file and truncate it while transferring it to himself, thus obtaining a copy of portions of system memory to which he would normally not have access.  Such memory might contain sensitive information, such as portions of the file cache or terminal buffers.  This information might be directly useful, or it might be leveraged to obtain elevated privileges in some way.  For example, a terminal buffer might include a user-entered password.

IV.  Workaround

No known workaround.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 4-STABLE or 5-STABLE, or to the RELENG_5_3, RELENG_4_11, RELENG_4_10, or RELENG_4_8 security branch dated after the correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 4.8, 4.10, 4.11, and 5.3 systems.

a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility.

[FreeBSD 4.x]
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:02/sendfile_4.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:02/sendfile_4.patch.asc

[FreeBSD 5.3]
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:02/sendfile_5.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:02/sendfile_5.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_4
  src/sys/ufs/ffs/ffs_inode.c                                    1.56.2.6
RELENG_4_11
  src/UPDATING                                              1.73.2.91.2.3
  src/sys/conf/newvers.sh                                   1.44.2.39.2.6
  src/sys/ufs/ffs/ffs_inode.c                               1.56.2.5.12.1
RELENG_4_10
  src/UPDATING                                              1.73.2.90.2.8
  src/sys/conf/newvers.sh                                   1.44.2.34.2.8
  src/sys/ufs/ffs/ffs_inode.c                               1.56.2.5.10.1
RELENG_4_8
  src/UPDATING                                             1.73.2.80.2.33
  src/sys/conf/newvers.sh                                  1.44.2.29.2.29
  src/sys/ufs/ffs/ffs_inode.c                                1.56.2.5.6.1
RELENG_5
  src/sys/ufs/ffs/ffs_inode.c                                    1.93.2.2
RELENG_5_4
  src/UPDATING                                             1.342.2.24.2.1
  src/sys/ufs/ffs/ffs_inode.c                                1.93.2.1.2.1
RELENG_5_3
  src/UPDATING                                            1.342.2.13.2.10
  src/sys/conf/newvers.sh                                  1.62.2.15.2.12
  src/sys/ufs/ffs/ffs_inode.c                                    1.93.4.1
- -------------------------------------------------------------------------

The latest revision of this advisory is available at ftp://ftp.freebsd.org/pub/CERT/advisories/FreeBSD-SA-05:02.sendfile.asc
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