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                         VSR Security Advisory
                       http://www.vsecurity.com/

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Advisory Name: Coda Filesystem Kernel Memory Disclosure
 Release Date: 2010-08-16
  Application: Coda kernel module for NetBSD and FreeBSD
     Versions: All known versions
     Severity: Medium
       Author: Dan Rosenberg < drosenberg (at) vsecurity (dot) com >
Vendor Status: Patch Released [2][3]
CVE Candidate: CVE-2010-3014
    Reference: http://www.vsecurity.com/resources/advisory/20100816-1/

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Product Description
- -------------------
- From [1]:

 "Coda is a distributed filesystem with its origin in AFS2.  It has many
 features that are very desirable for network filesystems.  Currently, Coda has
 several features not found elsewhere.

   1. disconnected operation for mobile computing
   2. is freely available under a liberal license
   3. high performance through client side persistent caching
   4. server replication
   5. security model for authentication, encryption and access control
   6. continued operation during partial network failures in server network
   7. network bandwidth adaptation
   8. good scalability
   9. well defined semantics of sharing, even in the presence of nework failure"


Vulnerability Overview
- ----------------------
On July 19th, VSR identified a vulnerability in the Coda filesystem kernel
module, as implemented for FreeBSD and NetBSD.  By sending a specially crafted
ioctl request to a mounted Coda filesystem, an unprivileged local user could
read large portions of kernel heap memory, leading to the disclosure of
potentially sensitive information.


Product Background
- ------------------
Coda is implemented as a kernel filesystem module with userland components.
System calls involving file I/O are passed to the Coda kernel module, which in
turn passes the request to the userland Venus cache manager via a character
device.  Venus answers the request by checking its cache or requesting content
from the Coda server.  Coda implements most standard filesystem operations,
including providing an ioctl interface. 


Vulnerability Details
- ---------------------
Coda ioctls are passed through the Coda filesystem module before being sent to
Venus.  The arguments to a Coda ioctl are encapsulated in a PioctlData struct,
which in turn contains a ViceIoctl struct.  The ViceIoctl struct contains
"in_size" and "out_size" fields, dictating the expected size of the input and
output data corresponding to a particular ioctl request.  The "in_size" field
is validated to prevent memory corruption via copying an unexpected amount of
data from userspace into a kernel buffer.  

However, the "out_size" field was missing this validation.  When copying the
output data of an ioctl request back to userspace, the "out_size" field was
used to determine the amount of data to copy, without restricting it to a
maximum possible size.  By specifying a large value for this field, the
contents of the kernel heap beyond the data intended to be returned to the user
would be copied into a userland buffer.  An unprivileged user could exploit
this to read large portions of the kernel heap, potentially disclosing
sensitive information.


Versions Affected
- -----------------
This vulnerability affects all known versions of the Coda filesystem module as
included in FreeBSD and NetBSD.  The Linux Coda module is not affected.


Vendor Response
- ---------------
The following timeline details FreeBSD's and NetBSD's response to the reported
issue:

2010-07-19    Vulnerability reported to FreeBSD and NetBSD
2010-07-20    Fix committed by NetBSD [2]
2010-07-21    Response from FreeBSD
2010-07-21    FreeBSD and NetBSD provided a draft advisory
2010-08-05    Fix committed by FreeBSD [3]
2010-08-16    Coordinated disclosure


Recommendation
- --------------

Coda users should apply the updates committed by NetBSD [2] and FreeBSD[3].


Common Vulnerabilities and Exposures (CVE) Information
- ------------------------------------------------------
The Common Vulnerabilities and Exposures (CVE) project has assigned
the number CVE-2010-3014 to this issue.  This is a candidates for
inclusion in the CVE list (http://cve.mitre.org), which standardizes
names for security problems.


Acknowledgements
- ----------------
Thanks to the FreeBSD and NetBSD security teams for their prompt responses.

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References:

1. Coda File System
 http://www.coda.cs.cmu.edu

2. Coda module in NetBSD CVS
 http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/coda/?only_with_tag=MAIN

3. FreeBSD SVN revision 210997
 http://svn.freebsd.org/viewvc/base?view=revision&revision=210997

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This advisory is distributed for educational purposes only with the sincere
hope that it will help promote public safety. This advisory comes with
absolutely NO WARRANTY; not even the implied warranty of merchantability or
fitness for a particular purpose. Virtual Security Research, LLC nor the author
accepts any liability for any direct, indirect, or consequential loss or damage
arising from use of, or reliance on, this information.

See the VSR disclosure policy for more information on our responsible
disclosure practices: http://www.vsecurity.com/company/disclosure

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     Copyright 2010 Virtual Security Research, LLC.  All rights reserved.

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