138 lines
5.3 KiB
Text
138 lines
5.3 KiB
Text
-----BEGIN PGP SIGNED MESSAGE-----
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Hash: SHA1
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=============================================================================
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FreeBSD-SA-13:13.nullfs Security Advisory
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The FreeBSD Project
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Topic: Cross-mount links between nullfs(5) mounts
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Category: core
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Module: nullfs
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Announced: 2013-09-10
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Credits: Konstantin Belousov
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Affects: All supported versions of FreeBSD.
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Corrected: 2013-09-10 10:07:21 UTC (stable/9, 9.2-STABLE)
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2013-09-10 10:08:20 UTC (releng/9.2, 9.2-RC1-p2)
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2013-09-10 10:08:20 UTC (releng/9.2, 9.2-RC2-p2)
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2013-09-10 10:08:20 UTC (releng/9.2, 9.2-RC3-p1)
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2013-09-10 10:15:33 UTC (releng/9.1, 9.1-RELEASE-p7)
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2013-09-10 10:12:09 UTC (stable/8, 8.4-STABLE)
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2013-09-10 10:14:19 UTC (releng/8.4, 8.4-RELEASE-p4)
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2013-09-10 10:13:14 UTC (releng/8.3, 8.3-RELEASE-p11)
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CVE Name: CVE-2013-5710
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For general information regarding FreeBSD Security Advisories,
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including descriptions of the fields above, security branches, and the
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following sections, please visit <URL:http://security.FreeBSD.org/>.
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I. Background
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The nullfs(5) filesystem allows all or a part of an already mounted
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filesystem to be made available in a different part of the global
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filesystem namespace. It is commonly used to make a set of files
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available to multiple chroot(2) or jail(2) environments without
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replicating the files in each environment. A common idiom, described
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in the FreeBSD Handbook, is to mount one subtree of a filesystem
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read-only within a jail's filesystem namespace, and mount a different
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subtree of the same filesystem read-write.
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II. Problem Description
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The nullfs(5) implementation of the VOP_LINK(9) VFS operation does not
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check whether the source and target of the link are both in the same
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nullfs instance. It is therefore possible to create a hardlink from a
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location in one nullfs instance to a file in another, as long as the
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underlying (source) filesystem is the same.
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III. Impact
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If multiple nullfs views into the same filesystem are mounted in
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different locations, a user with read access to one of these views and
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write access to another will be able to create a hard link from the
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latter to a file in the former, even though they are, from the user's
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perspective, different filesystems. The user may thereby gain write
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access to files which are nominally on a read-only filesystem.
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IV. Workaround
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No workaround is available, but systems which do not use the nullfs(5)
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filesystem, or do not null-mount different subtrees of the same source
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filesystem with different permissions, are not vulnerable.
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V. Solution
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Perform one of the following:
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1) Upgrade your vulnerable system to a supported FreeBSD stable or
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release / security branch (releng) dated after the correction date.
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2) To update your vulnerable system via a source code patch:
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The following patches have been verified to apply to the applicable
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FreeBSD release branches.
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a) Download the relevant patch from the location below, and verify the
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detached PGP signature using your PGP utility.
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# fetch http://security.FreeBSD.org/patches/SA-13:13/nullfs.patch
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# fetch http://security.FreeBSD.org/patches/SA-13:13/nullfs.patch.asc
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# gpg --verify nullfs.patch.asc
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b) Apply the patch.
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# cd /usr/src
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# patch < /path/to/patch
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c) Recompile your kernel as described in
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<URL:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
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system.
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3) To update your vulnerable system via a binary patch:
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Systems running a RELEASE version of FreeBSD on the i386 or amd64
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platforms can be updated via the freebsd-update(8) utility:
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# freebsd-update fetch
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# freebsd-update install
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VI. Correction details
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The following list contains the correction revision numbers for each
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affected branch.
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Branch/path Revision
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- -------------------------------------------------------------------------
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stable/8/ r255445
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releng/8.3/ r255446
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releng/8.4/ r255447
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stable/9/ r255443
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releng/9.1/ r255448
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releng/9.2/ r255444
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- -------------------------------------------------------------------------
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To see which files were modified by a particular revision, run the
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following command, replacing NNNNNN with the revision number, on a
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machine with Subversion installed:
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# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base
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Or visit the following URL, replacing NNNNNN with the revision number:
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<URL:http://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>
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VII. References
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<URL:http://www.freebsd.org/doc/en/books/handbook/jails-application.html>
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<URL:http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2013-5710>
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The latest revision of this advisory is available at
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<URL:http://security.FreeBSD.org/advisories/FreeBSD-SA-13:13.nullfs.asc>
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