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FreeBSD Security Advisories

2005-Apr-04 17:09 UTC

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

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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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Uwe Doering

2005-Apr-05 01:14 UTC

head link

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

FreeBSD Security Advisories wrote:> [...]
> 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
> [...]
The patch file (and CVS, too) contains this:

--------------------- cut here ----------------------
--- sys/ufs/ffs/ffs_inode.c     5 Feb 2002 18:35:03 -0000       1.56.2.5
+++ sys/ufs/ffs/ffs_inode.c     11 Mar 2005 14:29:19 -0000
@@ -197,6 +197,7 @@
  #endif
                         softdep_setup_freeblocks(oip, length);
                         vinvalbuf(ovp, 0, cred, p, 0, 0);
+                       vnode_pager_setsize(vp, 0);
                         oip->i_flag |= IN_CHANGE | IN_UPDATE;
                         return (ffs_update(ovp, 0));
                 }
--------------------- cut here ----------------------

I wonder, isn't the variable 'vp' actually supposed to be
'ovp' in the
added line?  Technically they are identical.  'ovp' is assigned from 
'vp' once in the variable definition section at the start of the
function.

However, using 'vp' when calling vnode_pager_setsize() looks a little 
odd given that anywhere else in this function, including another call to 
vnode_pager_setsize(), the variable 'ovp' is used instead of
'vp'.

I can't tell why 'ovp' was introduced in the first place.  Might
have
historical reasons.  But that's how the code currently works.  In the 
MAIN branch as well, according to CVS.  So I'd suggest to replace
'vp'
with 'ovp' in the patch above, for the sake of clarity and consistency.

    Uwe
-- 
Uwe Doering         |  EscapeBox - Managed On-Demand UNIX Servers
gemini@geminix.org  |  http://www.escapebox.net

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