231 lines
9.5 KiB
HTML
231 lines
9.5 KiB
HTML
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<title>Profile Registry Leak</title>
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<o:Author>Alex Armanasu</o:Author>
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<div class=Section1>
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<p class=MsoNormal align=center style='text-align:center'>Profile Registry Leak</p>
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<p class=Paragraph>This document describes a proposed solution to the registry
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leak problem that we could not fix for Windows 2000.<span style="mso-spacerun:
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yes"><EFBFBD> </span>Bugs 173929 and 435236 are partly caused by the registry
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leak.<span style="mso-spacerun: yes"><EFBFBD> </span>Here is one example of the
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problem.<span style="mso-spacerun: yes"><EFBFBD> </span>When a user logs off, userenv
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tries to unload the user's profile.<span style="mso-spacerun: yes"><EFBFBD>
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</span>Sometimes some process has a key open in the registry.<span
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style="mso-spacerun: yes"><EFBFBD> </span>This prevents userenv from unloading the
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hive.<span style="mso-spacerun: yes"><EFBFBD> </span>The spreadsheet below lists most
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of the known causes of the bug.</p>
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src="./registry%20leak_files/image002.gif" v:shapes="_x0000_i1025"><![endif]><!--[if gte mso 9]><xml>
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<p class=Paragraph>This bug has three symptoms that affect users.<span
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style="mso-spacerun: yes"><EFBFBD> </span>First, if userenv cannot unload the profile
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when the user logs off, userenv does not save the user's profile to the
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server.<span style="mso-spacerun: yes"><EFBFBD> </span>Second, since such profiles
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never get unloaded, they end up using a lot of memory on a terminal server that
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has lots of users logging in.<span style="mso-spacerun: yes"><EFBFBD> </span>Third, if
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the profile is still loaded the next time the user logs in, any changes stored
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on the server are not loaded and are lost.</p>
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<p class=Paragraph>I have a separate solution for each symptom.<span
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style="mso-spacerun: yes"><EFBFBD> </span>Currently when a user logs off, if the profile
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is locked we poll the profile for 60 seconds before giving up.<span
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style="mso-spacerun: yes"><EFBFBD> </span>I would change the code to use RegSaveKey to
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save the hive at the end of the 60 second delay rather then giving up.</p>
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<p class=Paragraph>To solve the second symptom, the memory leak, I propose
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using a new API that will soon be checked in.<span style="mso-spacerun: yes"><EFBFBD>
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</span>With this API we can tell the registry to set an event when no one is
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using the specified hive.<span style="mso-spacerun: yes"><EFBFBD> </span>At that point
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we can unload the hive.<span style="mso-spacerun: yes"><EFBFBD> </span>Our code would
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change so that after waiting 60 seconds for a hive to be unlocked, we would use
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the new API to receive notice when the hive was finally free.<span
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style="mso-spacerun: yes"><EFBFBD> </span>We would have to add a thread to wait for each
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group of 64 hives (WaitForMultipleObjects can only wait for 64 events).<span
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style="mso-spacerun: yes"><EFBFBD> </span>We would have to add code to tell the helper
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thread which hives to wait for.<span style="mso-spacerun: yes"><EFBFBD> </span>We
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would have to add code to synchronize the helper thread and LoadUserProfile in
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the case where the user logs back in before the hive gets unloaded.<span
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style="mso-spacerun: yes"><EFBFBD> </span>This does not completely solve the problem
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because wininet never releases some of the keys that it uses.<span
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style="mso-spacerun: yes"><EFBFBD> </span>However it makes sure that we behave
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correctly should wininet ever get fixed.<span style="mso-spacerun: yes"><EFBFBD>
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</span>We can show the terminal server team what dlls are leaking registry keys
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and they can spend the time getting the dlls fixed.</p>
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<p class=Code>NtUnloadKeyEx(<o:p></o:p></p>
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<p class=Code><span style="mso-spacerun: yes"><EFBFBD><EFBFBD><EFBFBD> </span>IN POBJECT_ATTRIBUTES
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TargetKey,<o:p></o:p></p>
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<p class=Code><span style="mso-spacerun: yes"><EFBFBD><EFBFBD><EFBFBD> </span>IN HANDLE Event
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OPTIONAL<o:p></o:p></p>
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<p class=Code><span style="mso-spacerun: yes"><EFBFBD><EFBFBD><EFBFBD> </span>)<o:p></o:p></p>
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<p class=Paragraph>It is unclear if we should solve the last symptom.<span
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style="mso-spacerun: yes"><EFBFBD> </span>Currently userenv does not handle overlapped
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logon sessions well.<span style="mso-spacerun: yes"><EFBFBD> </span>Userenv will lose
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one set of changes.<span style="mso-spacerun: yes"><EFBFBD> </span>A solution to that
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problem would probably solve this problem.<span style="mso-spacerun: yes"><EFBFBD>
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</span>We could solve this problem by using another new API.<span
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style="mso-spacerun: yes"><EFBFBD> </span>This API will let us rename a key even when
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it is in use.<span style="mso-spacerun: yes"><EFBFBD> </span>If a user logs on and his
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hive is loaded because the user has another logon session on the machine, we will
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use the loaded hive and lose any changes on the server.<span
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style="mso-spacerun: yes"><EFBFBD> </span>If a user logs on and his hive is loaded
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because some program still has a key open from the last logon session (or some
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program has loaded the hive for its own use), then we will rename the key and
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load the profile from the server.<span style="mso-spacerun: yes"><EFBFBD> </span>This
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requires that we change our code as described above.<span style="mso-spacerun:
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yes"><EFBFBD> </span>Unfortunately, since the name ntuser.dat is already taken, we
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need to use a new name for the hive from the server and remember that when the
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user logs out.<span style="mso-spacerun: yes"><EFBFBD> </span>At that time we need to
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make sure we copy the new hive and attempt to delete the old hive.<span
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style="mso-spacerun: yes"><EFBFBD> </span>We need to handle the case where the user
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has multiple hives leaked simultaneously.</p>
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<p class=Code>NTSTATUS<o:p></o:p></p>
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<p class=Code>NtRenameKey(<o:p></o:p></p>
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<p class=Code><span style="mso-spacerun: yes"><EFBFBD><EFBFBD><EFBFBD> </span>IN HANDLE<span
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style="mso-spacerun: yes"><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> </span>KeyHandle,<o:p></o:p></p>
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<p class=Code><span style="mso-spacerun: yes"><EFBFBD><EFBFBD><EFBFBD> </span>IN
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PUNICODE_STRING<span style="mso-spacerun: yes"><EFBFBD> </span>NewName<o:p></o:p></p>
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<p class=Code><span style="mso-spacerun: yes"><EFBFBD><EFBFBD><EFBFBD> </span>)<o:p></o:p></p>
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