[Full-Disclosure] FreeBSD Security Advisory FreeBSD-SA-04:01.mksnap_ffs

From: FreeBSD Security Advisories (security-advisories_at_freebsd.org)
Date: 01/30/04

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    To: FreeBSD Security Advisories <security-advisories@freebsd.org>
    Date: Fri, 30 Jan 2004 08:07:12 -0800 (PST)
    
    

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    =============================================================================
    FreeBSD-SA-04:01.mksnap_ffs Security Advisory
                                                              The FreeBSD Project

    Topic: mksnap_ffs clears file system options

    Category: core
    Module: mksnap_ffs
    Announced: 2004-01-30
    Credits: Kimura Fuyuki <fuyuki@nigredo.org>
                    Wiktor Niesiobedzki <bsd@w.evip.pl>
    Affects: FreeBSD 5.1-RELEASE
                    FreeBSD 5.2-RELEASE
    Corrected: 2004-01-27 19:33:16 UTC (RELENG_5_1, 5.1-RELEASE-p12)
                    2004-01-29 22:54:31 UTC (RELENG_5_2, 5.2-RELEASE-p1)
    CVE Name: CAN-2004-0099
    FreeBSD only: YES

    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

    Mounted filesystems can have a variety of flags set on them. Some
    flags affect performance and reliability, while others enable or
    disable particular security-related features such as the ability to
    execute a binary stored on the filesystem or the use of access control
    lists to complement normal Unix file permissions.

    The mksnap_ffs(8) command creates a `snapshot' of a filesystem. A
    `snapshot' is a static representation of the state of the filesystem
    at a particular point in time. Snapshots have a variety of uses,
    but their primary purpose is to make it possible to run fsck(8) and
    dump(8) on live filesystems.

    II. Problem Description

    The kernel interface for creating a snapshot of a filesystem is the
    same as that for changing the flags on that filesystem. Due to an
    oversight, the mksnap_ffs(8) command called that interface with only
    the snapshot flag set, causing all other flags to be reset to the
    default value.

    III. Impact

    A regularly scheduled backup of a live filesystem, or any other
    process that uses the mksnap_ffs(8) command (for instance, to provide
    a rough undelete functionality on a file server), will clear any flags
    in effect on the filesystem being snapshot. Possible consequences
    depend on local usage, but can include disabling extended access
    control lists or enabling the use of setuid executables stored on an
    untrusted filesystem.

    The mksnap_ffs(8) command is normally only available to the superuser
    and members of the `operator' group. There is therefore no risk
    of a user gaining elevated privileges directly through use of the
    mksnap_ffs(8) command unless it has been intentionally made available
    to unprivileged users.

    IV. Workaround

    Do not use the mksnap_ffs(8) command, nor the -L option of the dump(8)
    command.

    It is recommended that you delete the mksnap_ffs(8) command from your
    system to prevent accidental use:

    # rm /sbin/mksnap_ffs

    V. Solution

    Do one of the following:

    1) Upgrade your vulnerable system to the RELENG_5_1 or RELENG_5_2
    security branch dated after the correction date.

    NOTE WELL: Due to release engineering in progress at the time of this
               writing, the RELENG_5_2 security branch (5.2-RELEASE-p1)
               also includes numerous other critical bug fixes, most of
               which are not security related. Please read src/UPDATING
               for details on these changes.

    2) To patch your present system:

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

    [FreeBSD 5.1 systems]
    # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-04:01/mksnap_ffs_5_1.patch
    # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-04:01/mksnap_ffs_5_1.patch.asc

    [FreeBSD 5.2 systems]
    # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-04:01/mksnap_ffs_5_2.patch
    # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-04:01/mksnap_ffs_5_2.patch.asc

    b) Execute the following commands as root:

    # cd /usr/src
    # patch < /path/to/patch
    # cd /usr/src/sbin/mksnap_ffs
    # make obj && make depend && make && make install

    You are strongly encouraged to verify that all your filesystems have
    the correct flags set. The mount(8) command can list currently mounted
    filesystems and flags. Run the following command as root:

    # mount

    VI. Correction details

    The following list contains the revision numbers of each file that was
    corrected in FreeBSD.

    Branch Revision
      Path
    - -------------------------------------------------------------------------
    RELENG_5_1
      src/sbin/mksnap_ffs/mksnap_ffs.c 1.2.2.1
      src/sys/conf/newvers.sh 1.50.2.14
    RELENG_5_2
      src/sbin/mksnap_ffs/mksnap_ffs.c 1.5.2.1
      src/sys/conf/newvers.sh 1.56.2.3
    - -------------------------------------------------------------------------
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