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UNIRAS Brief - 46/04 - FreeBSD Security Bulletin - FreeBSD-SA-04:01.mksnap_ffs mksnap_ffs clears file system options


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   UNIRAS (UK Govt CERT) Briefing Notice - 46/04 dated 04.02.04  Time: 14:00
 UNIRAS is part of NISCC(National Infrastructure Security Co-ordination Centre)
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  UNIRAS material is also available from its website at www.uniras.gov.uk and
         Information about NISCC is available from www.niscc.gov.uk
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FreeBSD Security Bulletin:

ESB-2004.0081 -- FreeBSD-SA-04:01.mksnap_ffs mksnap_ffs clears file system options


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.

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@xxxxxxxxxxx>
                Wiktor Niesiobedzki <bsd@xxxxxxxxx>
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

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)

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
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UNIRAS wishes to acknowledge the contributions of FreeBSD for the information
contained in this Briefing. 
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This Briefing contains the information released by the original author. Some 
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