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FreeBSD-SA-14:05.nfsserver                                  Security Advisory
                                                          The FreeBSD Project

Topic:          Deadlock in the NFS server

Category:       core
Module:         nfsserver
Announced:      2014-04-08
Credits:        Rick Macklem
Affects:        All supported versions of FreeBSD.
Corrected:      2014-04-08 18:27:39 UTC (stable/10, 10.0-STABLE)
                2014-04-08 18:27:46 UTC (releng/10.0, 10.0-RELEASE-p1)
                2014-04-08 23:16:19 UTC (stable/9, 9.2-STABLE)
                2014-04-08 23:16:05 UTC (releng/9.2, 9.2-RELEASE-p4)
                2014-04-08 23:16:05 UTC (releng/9.1, 9.1-RELEASE-p11)
                2014-04-08 23:16:19 UTC (stable/8, 8.4-STABLE)
                2014-04-08 23:16:05 UTC (releng/8.4, 8.4-RELEASE-p8)
                2014-04-08 23:16:05 UTC (releng/8.3, 8.3-RELEASE-p15)
CVE Name:       CVE-2014-1453

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 Network File System (NFS) allows a host to export some or all of its
file systems so that other hosts can access them over the network and mount
them as if they were on local disks.  FreeBSD includes both server and client
implementations of NFS.

II.  Problem Description

The kernel holds a lock over the source directory vnode while trying to
convert the target directory file handle to a vnode, which needs to be
returned with the lock held, too.  This order may be in violation of normal
lock order, which in conjunction with other threads that grab locks in the
right order, constitutes a deadlock condition because no thread can proceed.

III. Impact

An attacker on a trusted client could cause the NFS server become deadlocked,
resulting in a denial of service.

IV.  Workaround

Systems that do not provide NFS services are not vulnerable.  Neither
are systems that do but use the old NFS implementation, which is the
default in FreeBSD 8.x.

To determine which implementation an NFS server is running, run the
following command:

# kldstat -v | grep -cw nfsd

This will print 1 if the system is running the new NFS implementation,
and 0 otherwise.

To switch to the old NFS implementation:

1) Append the following lines to /etc/rc.conf:

   nfsv4_server_enable="no"
   oldnfs_server_enable="yes"

2) If the NFS server is compiled into the kernel (which is the case
   for the stock GENERIC kernel), replace the NFSD option with the
   NFSSERVER option, then recompile your kernel as described in
   <URL:http://www.FreeBSD.org/handbook/kernelconfig.html>.

   If the NFS server is not compiled into the kernel, the correct
   module will be loaded at boot time.

3) Finally, reboot the system.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

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

# fetch http://security.FreeBSD.org/patches/SA-14:05/nfsserver.patch
# fetch http://security.FreeBSD.org/patches/SA-14:05/nfsserver.patch.asc
# gpg --verify nfsserver.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.

3) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/8/                                                         r264285
releng/8.3/                                                       r264284
releng/8.4/                                                       r264284
stable/9/                                                         r264285
releng/9.1/                                                       r264284
releng/9.2/                                                       r264284
stable/10/                                                        r264266
releng/10.0/                                                      r264267
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:http://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-1453>

The latest revision of this advisory is available at
<URL:http://security.FreeBSD.org/advisories/FreeBSD-SA-14:05.nfsserver.asc>
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