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Category:   OS (Linux)  >   Red Hat Global File System Vendors:   Red Hat
Red Hat Global File System gfs_lock() Lets Local Users Deny Service
SecurityTracker Alert ID:  1023812
SecurityTracker URL:
CVE Reference:   CVE-2010-0727   (Links to External Site)
Date:  Apr 1 2010
Impact:   Denial of service via local system
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): RHEL 5.5
Description:   A vulnerability was reported in Red Hat Global File System. A local user can cause denial of service conditions.

On a system that has a Global File System (GFS) mounted, a local user can exploit a flaw in the gfs_lock() implementation to trigger a kernel panic.

Impact:   A local user can cause a kernel panic on the target system.
Solution:   Red Hat has issued a fix for gfs-kmod for Red Hat Enterprise Linux 5.5.

The Red Hat advisory is available at:

Vendor URL: (Links to External Site)
Cause:   State error

Message History:   This archive entry is a follow-up to the message listed below.
Apr 1 2010 Red Hat Global File System gfs_lock() Lets Local Users Deny Service

 Source Message Contents

Subject:  [RHSA-2010:0291-04] Moderate: gfs-kmod security, bug fix and enhancement update

Hash: SHA1

                   Red Hat Security Advisory

Synopsis:          Moderate: gfs-kmod security, bug fix and enhancement update
Advisory ID:       RHSA-2010:0291-04
Product:           Red Hat Enterprise Linux
Advisory URL:
Issue date:        2010-03-30
CVE Names:         CVE-2010-0727 

1. Summary:

Updated gfs-kmod packages that fix one security issue, numerous bugs, and
add one enhancement are now available for Red Hat Enterprise Linux 5.5,
kernel release 2.6.18-194.el5.

The Red Hat Security Response Team has rated this update as having moderate
security impact. A Common Vulnerability Scoring System (CVSS) base score,
which gives a detailed severity rating, is available from the CVE link in
the References section.

2. Relevant releases/architectures:

RHEL Cluster-Storage (v. 5 server) - i386, ia64, ppc, x86_64

3. Description:

The gfs-kmod packages contain modules that provide the ability to mount and
use GFS file systems.

A flaw was found in the gfs_lock() implementation. The GFS locking code
could skip the lock operation for files that have the S_ISGID bit
(set-group-ID on execution) in their mode set. A local, unprivileged user
on a system that has a GFS file system mounted could use this flaw to cause
a kernel panic. (CVE-2010-0727)

These updated gfs-kmod packages are in sync with the latest kernel
(2.6.18-194.el5). The modules in earlier gfs-kmod packages failed to load
because they did not match the running kernel. It was possible to
force-load the modules. With this update, however, users no longer need to.

These updated gfs-kmod packages also fix the following bugs:

* when SELinux was in permissive mode, a race condition during file
creation could have caused one or more cluster nodes to be fenced and lock
the remaining nodes out of the GFS file system. This race condition no
longer occurs with this update. (BZ#471258)

* when ACLs (Access Control Lists) are enabled on a GFS file system, if a
transaction that has started to do a write request does not have enough
spare blocks for the operation it causes a kernel panic. This update
ensures that there are enough blocks for the write request before starting
the operation. (BZ#513885)

* requesting a "flock" on a file in GFS in either read-only or read-write
mode would sometimes cause a "Resource temporarily unavailable" state error
(error 11 for EWOULDBLOCK) to occur. In these cases, a flock could not be
obtained on the file in question. This has been fixed with this update so
that flocks can successfully be obtained on GFS files without this error
occurring. (BZ#515717)

* the GFS withdraw function is a data integrity feature of GFS file systems
in a cluster. If the GFS kernel module detects an inconsistency in a GFS
file system following an I/O operation, the file system becomes unavailable
to the cluster. The GFS withdraw function is less severe than a kernel
panic, which would cause another node to fence the node. With this update,
you can override the GFS withdraw function by mounting the file system with
the "-o errors=panic" option specified. When this option is specified, any
errors that would normally cause the system to withdraw cause the system to
panic instead. This stops the node's cluster communications, which causes
the node to be fenced. (BZ#517145)

Finally, these updated gfs-kmod packages provide the following enhancement:

* the GFS kernel modules have been updated to use the new generic freeze
and unfreeze ioctl interface that is also supported by the following file
systems: ext3, ext4, GFS2, JFS and ReiserFS. With this update, GFS supports
freeze/unfreeze through the VFS-level FIFREEZE/FITHAW ioctl interface.

Users are advised to upgrade to these latest gfs-kmod packages, updated for
use with the 2.6.18-194.el5 kernel, which contain backported patches to
correct these issues, fix these bugs, and add this enhancement.

4. Solution:

Before applying this update, make sure all previously-released errata
relevant to your system have been applied.

This update is available via the Red Hat Network. Details on how to
use the Red Hat Network to apply this update are available at

5. Bugs fixed (

471258 - fatal: assertion "gfs_glock_is_locked_by_me(gl) && gfs_glock_is_held_excl(gl)" failed
487610 - GFS: Change gfs freeze/unfreeze to use new standard
513885 - GFS kernel panic, suid + nfsd with posix ACLs enabled
515717 - Flock on GFS fs file will error with "Resource tempory unavailable" for EWOULDBLOCK
517145 - [RFE] GFS: New mount option: -o errors=withdraw|panic
570863 - CVE-2010-0727 bug in GFS/GFS2 locking code leads to dos

6. Package List:

RHEL Cluster-Storage (v. 5 server):






These packages are GPG signed by Red Hat for security.  Our key and 
details on how to verify the signature are available from

7. References:

8. Contact:

The Red Hat security contact is <>.  More contact
details at

Copyright 2010 Red Hat, Inc.
Version: GnuPG v1.4.4 (GNU/Linux)


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