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Attachment #38088
sec-openwbem-arch.html	text/html	2005-05-25 10:33:54 UTC	8.24 KB	no flags	Details

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  <title>Outline of New Secure OpenWBEM Architecture</title>
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<h1>Outline of New Secure OpenWBEM Architecture</h1>
<p>Kevin Van Horn</p>
<p>Dan Nuffer<br>
</p>
<p><br>
Note: a &#8220;passive&#8221; provider is an instance provider, secondary
instance provider, method provider, or associator provider.
</p>
<h2>The CIMOM is now a collection of processes.</h2>
<p>
Separate processes act as bulkheads to limit the damage that may be
caused
by bugs and exploits.
</p>
<p>
Privileges of a subsystem limited based on userid of its process.
</p>
<p>
Wherever practical, code runs only with the userid of the entity that
initiated the operation.
</p>
<p>
Only a small amount of code, in 2 subsystems &#8212; the monitor and the
connection handler &#8212; runs as root.
</p>
<h2>Decomposition into subsystems</h2>
<p>Below are the various processes that comprise the CIMOM. Those that
persist for the entire time the CIMOM is running are marked with P
(persistent); those that last for only the duration of a single CIMOM
request
(or less) are marked with T (transient); others of intermediate
duration are
marked with S (semipermanent).</p>
<ul>
  <li>Monitor [P].
  </li>
  <li>Logger [P].
  </li>
  <li>Repository Server [P] (RS).
  </li>
  <li>Indication Server [P] (IS).
  </li>
  <li>Indication provider processes [S] (IPP).
  </li>
  <li>Pseudo Random Number Server [P] (PRNS).
  </li>
  <li>Connection Handler Creator [P] (CHC).
  </li>
  <li>Connection handlers [T] (CH).
  </li>
  <li>User provider processes [T] (UPP).
  </li>
</ul>
<h2>The Monitor</h2>
<p>The Monitor may grant other subsystems (OpenWBEM processes) limited
capabilities that they would not otherwise have.</p>
<p>Monitor knows identity of a subsystem process because it created the
process and created a Unix domain socket pair for communicating with it.</p>
<p>The sendmsg / recvmsg systems calls used to pass descriptors from
monitor to
subsystem process.</p>
<p>Kinds of requests a subsystem process might make to monitor:</p>
<ul>
  <li>Open a file for reading, or writing, or both, and return the file
descriptor.
  </li>
  <li>Create a file with given permissions and user, and return the
file
descriptor for writing it.
  </li>
  <li>Give ownership of a file to root. (The logger subsystem needs
this to
ensure that only root can read log files.)
  </li>
  <li>Fork a process running an executable as a particular user and
return fds
for stdin, stdout, and stderr. (This includes specification of a
timeout, so
the monitor can kill the new process if it hangs.)
  </li>
  <li>Grant one subsystem access to another subsystem. It does this by
creating
a Unix-domain socket pair, passing one socket descriptor to the
subsystem to
the subsystem providing a service, and the other socket descriptor to
the
subsystem requesting the service.
  </li>
  <li>Other requests related to authentication of users request an
operation from
the CIMOM.
  </li>
</ul>
<p>Monitor has its own access control lists that specify what requests
a
particular subsystem process can make (includes allowable arguments).
This may
also take into account the sequence of requests the subsystem has made,
using
a FSM.</p>
<p>If subsystem makes a disallowed request, the monitor will no longer
accept
requests from the subsystem. (Should it go so far as to kill the
process?)<br>
</p>
<p>All startup/shutdown/restart activity is coordinated by the monitor<br>
</p>
<h2>The Logger</h2>
<p> Runs as the OpenWBEM-Logger user. All logging is done
by sending a message to the logger. All processes created by the
monitor are given a descriptor for sending messages to the logger.
After
creating a log file, but before writing to it, the logger asks the
monitor to
change its owner to root so that only root can read the log output. </p>
<h2>The Repository Server</h2>
<p> Runs as the OpenWBEM-Repository user. All
repository files are owned by this user, and accessible only by owner.
The
repository holds access control lists that control what operations are
alowed
based on userid, groupid?, namespace, and class. When the monitor
grants a
process access to the repository server, it associates the userid of
the
requester with the descriptor it passes to the repository server. The
access
control lists are implemented as CIM instances in the repository. The
repository also contains information identifying which providers are
associated with a class. </p>
<h2>The Pseudo Random Number Server</h2>
<p>This process exists only on platforms that lack an acceptable
<tt>/dev/urandom</tt> or its equivalent. It runs a cryptographically
strong
pseudo-random number generator, seeded by the output of an entropy
collector.
(Do we restrict access to this server in some way to prevent DOS
attacks?)
</p>
<h2>Connection Handlers and Connection Handler Creator</h2>
<p>The Connection Handler Creator accepts connections to the CIMOM, and
for
each connection it forks off a connection handler process. (The purpose
of
the CHC is to reduce startup times, as it has already done the
initialization
the CH process will need.) The CH and CHC processes run as root. A CH
process is
responsible for parsing HTTP headers sufficiently to carry out
authentication, as well as doing SSL client authentication (the reason
it isn't a security advantage to run as a non-privileged user). Once
authentication has
occurred it changes to the appropriate userid. Then, the request is
parsed and the operations requested of the CIMOM are performed, doing
as much of the work itself as is practical. It runs as the user making
the
request, as determined in the authentication phase. It accesses the
repository server for operations on static data and to find out what
providers
(if any) it must use to carry out the operation.</p>
<p> The CH loads and runs any needed passive providers; hence these
providers
can only do whatever the requesting user is authorized to do. These
providers
may in turn request certain capabilities (typically file descriptors
opened
for reading) from the monitor; these capabilities will be granted or
not
depending on the userid of the process.</p>
<p>Some passive providers may run as independent processes because they
are
implemented in a scripting language (e.g., Perl) or to be isolated from
C++
binary compatibility problems. These run with the same userid as the
CH, and
again request from the Monitor any special capabilities they may need.</p>
<h2>User Provider Processes</h2>
<p> Described above under &#8220;Connection Handlers&#8221;</p>
<h2>Indication Server</h2>
<p> Runs as the OpenWBEM-indication-server user. Handles activation and
deactivation of indication providers and runs indication export
providers and
subscription filters (the &#8220;where&#8221; clause).</p>
<p>When a CH process requests creation of an indication subscription,
the indication server first contacts the repository server to determine
if
that user has permission to receive indications of the requested
indication
class, processed by the (provider for the) requested indication handler
class.
If so, it sends the appropriate activate message to the appropriate
indication
provider process, asking the monitor to create the process if it
doesn't
already exist, and updates its internal data structures for handling
indications.</p>
<p>When asked to remove a subscription, the indication server checks to
see if
the requester's userid is either explicitly authorized to remove the
subscription (based on indication class and indication handler class)
or is
the same userid used to create the subscription. If so, it sends the
appropriate deactivate message to the indication provider, and updates
its
internal data structures for handling indications.</p>
<p>The indication server receives all indications generated by
indication
providers and runs the appropriate indication export providers to
process
them.</p>
<h2>Indication Provider Processes</h2>
<p>There is one of these for each active indication provider. An IPP
runs the
code for an indication provider, sending the generated indications to
the
indication server. It may request certain capabilities (typically file
descriptors opened for reading) from the Monitor; these capabilities
will be
granted or not depending on which indication provider is requesting
them.</p>
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Attachment #39970
Audit report	application/pdf	2005-06-27 10:07:51 UTC	38.30 KB	no flags	Details

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Attachment #45841
patch for buffer overflow vulnerabilities	patch	2005-08-11 22:33:34 UTC	2.22 KB	no flags	Details

Attachment #47461
new patch	patch	2005-08-24 20:02:51 UTC	7.57 KB	no flags	Details