Abstract:
A system and method for identity decisions and invalidation. Modified objects (e.g., files, executables, etc.) are flagged for reevaluation. Privileges associated with the object are only persisted if the modifications are determined to be authorized (e.g., updates and patches). In one embodiment, a tagging system registers to be notified of all writes, renames, truncations, moves, deletions, or any other relevant modifications to objects. If the tagging system detects a modification operation targeting the object, it invalidates all identity decisions cached with the object. The next time the object runs, the system does not recognize the object and it is forced to reevaluate its identity. Thus, patching and other write operations are still permitted, but the system detects the changed object and reevaluates the identity.

Description:
FIELD OF THE INVENTION 
   The embodiment of the present invention relates to identities in a computer system, and more particularly, to a system and method for identity decisions and invalidation. 
   BACKGROUND OF THE INVENTION 
   Spoofing and impersonation software attacks take advantage of the privileges assigned to executable objects to achieve their nefarious ends. Typically, the attack modifies the executable to perform the malicious acts using (implicit or explicit) privileges or capabilities associated with the unmodified executable. This vulnerability can be addressed by altering the ACL governing the executable to make it non-writable, but this approach also prevents patching and upgrading of the executable. 
   The embodiment of the present invention is directed to providing a system and method that overcome the foregoing and other disadvantages. More specifically, the present invention is directed to an improved system and method for identity decisions and invalidation. 
   SUMMARY OF THE INVENTION 
   A system and method for identity decisions and invalidation is provided. Related methods are described in U.S. patent application Ser. No. 10/938,126, filed Sep. 10, 2004, U.S. patent application Ser. No. 10/963,479, filed Oct. 12, 2004, and U.S. patent application Ser. No. 10/868,183, filed Jun. 15, 2004, each of which is hereby incorporated by reference in its entirety. In accordance with one aspect of the invention, modified objects are flagged for reevaluation. Privileges and decisions associated with the object are only persisted if the modifications are determined to be authorized (e.g., updates and patches). In one embodiment, a tagging system registers to be notified of all writes, renames, truncations, moves, deletions, and any other relevant modifications to the object. If the tagging system detects a modification operation targeting the object, it invalidates all identity decisions cached with the object. The next time the object runs, the system does not recognize the object and it is forced to reevaluate its identity. Thus, patching and other write operations are still permitted, but the system detects the changed object and reevaluates the identity. It will be appreciated that the embodiment of the present invention is intended as an improvement on computing a hash or signature of the object and checking the object each time it is executed, because, in the absence of any writes, there is no significant per run computational cost. This avoids slowing down normal process creation, DLL loads, or other file accesses while computing the hash. Additional implementations may also be envisioned in which the system responds to the appropriate notifications that the target object has/will/might change by deleting the corresponding identity data stored for the target object. 
   In accordance with another aspect of the invention, the system includes an ID engine, a sources ID manifest, decision makers, a metadata cache, and metadata providers (policy engines). The ID engine generates identifications for particular applications and the objects, such as executables, associated with them, and may include a detection component, a protection component, an invalidation component, and a cache for object/identity. The identification engine and decision makers may exchange information regarding objects and identifications. The decision makers and metadata cache may exchange information regarding identifications and metadata. The metadata cache may include an invalidation engine, which is used to invalidate the identity metadata that is cached for an object when a change is detected to the object. 
   In accordance with another aspect of the invention, a per-identity table and a global current sequence number table are maintained. The sequence numbers of the tables are associated with metadata providers, which provide information about the innate characteristics of the application as well as encapsulating explicit policies of the system. A sequence number from the per identity table for an associated provider is compared to the corresponding sequence number from the global current sequence number table to determine if the provider will be invoked to generate current metadata for the identity. 
   In accordance with another aspect of the invention, for untrusted media, such as removable media or an insecure file system, such as FAT, the system may detect that the object is stored on untrusted media, and copy the target object into a trusted directory (perhaps on non-removable or otherwise secured media, such as an NTFS directory with proper ACLs). The identity may then be recomputed on the trusted copy. A determination may then be made as to whether the system has notifications for media removal and media arrival (as well as across system reboots). If the system has such notifications, then the ID may be cached. If the system does not have such notifications, then the ID may not be cached (in other words, the local copy may essentially be thrown out in that it will not have a cached ID and will have to be recopied and have the ID recomputed each time.) The identification is then returned. In a system which has notifications for media removal (as well as across system reboots), if a notification of media removal (or change notification in some file systems) or reboot is received, then the media&#39;s cache may be invalidated. It will be appreciated that other embodiments of this routine for untrusted media may also be envisioned, and that the general point is that the correctness of the system depends on reliable change notifications, which prompt the invalidation of the media&#39;s cache. A media removal notification is one example, a per-file change notification is another. In many systems, such reliable change notifications may be available. In cases where they are not, whether it is because the media doesn&#39;t support a removal notice or the file system doesn&#39;t support the necessary per-file changes, or in general if the file system is not trusted, the fall back is the “recomputed on every run” alternative described above where the ID is not cached and is recomputed each time. In general the “recomputed on every run” alternative will be slower, but may be preferred in cases where reliable change notifications are not available. 
   In accordance with another aspect of the invention, for a network volume system, the operating system may detect such volumes and copy the object into a secure directory (on the local system or to a trusted network location). If the remote system or object store is not trusted, or if a determination is made that the object was changed during the copying, then the identity is recomputed on the trusted copy. If the system and object are trusted, and if there were no changes to the object during the copying, then the identification is obtained from the trusted system. With regard to this routine for network volumes, it will be appreciated that in one embodiment a local copy does not need to be made for all network volumes. Instead, a local copy is only made for untrusted network volumes. If the remote machine is trusted, and if the remote machine is able to send reliable change notifications, then the system doesn&#39;t have to fall back to copying it locally and recomputing the identification every time. Instead, it may be treated like a file on a trusted local volume. 
   In accordance with another aspect of the invention, for a multi-boot system, the tagging system stores a unique identifier denoting the current executing operating system to uniquely denote which operating system is identified and the associated data for the object. When the system accesses the stored data, the currently executing operating system identification gets checked against the stored operating system identification with the data. If there is a mismatch of operating system IDs, then the system invalidates the stored identity and data and reevaluates the object&#39;s identity and stores the current data along with the current operating system identification. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a block diagram of a system for identity decisions and invalidations; 
       FIG. 2A  is a diagram of a per-identity table; 
       FIG. 2B  is a diagram of a global current sequence number table; 
       FIG. 3  is a flow diagram illustrative of a general routine for obtaining valid decision metadata for an identity utilizing the tables of  FIGS. 2A and 2B ; 
       FIG. 4  is a flow diagram illustrative of a routine for retrieving decision metadata for an object; 
       FIG. 5  is a flow diagram illustrative of a routine for the revocation of identity data associated with an object based on notification of changes to the object, e.g. by a filter; 
       FIGS. 6A and 6B  are flow diagrams illustrative of a routine for associating identities with objects on removable media; 
       FIG. 7  is a flow diagram illustrative of a routine for associating identities with objects on network volumes; and 
       FIG. 8  is a flow diagram illustrative of a routine for associating identities with objects in a multi-boot system. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  is a block diagram of an identity decision system  100  in accordance with the embodiment of the present invention. As shown in  FIG. 1 , the identity decision system  100  includes an ID engine  110 , a sources ID manifest  120 , decision makers  130 , a metadata cache  140 , and metadata providers  150 . The ID engine  110  generates identifications and may include a detection component  112 , a protection component  114 , an invalidation component  116 , and an object identity cache  118 . The identification engine  110  and decision makers  130  exchange information regarding objects and identifications. The decision makers  130  and metadata cache  140  exchange information regarding identifications and metadata. The metadata cache  140  includes an invalidation engine  142 , which is utilized to invalidate identity metadata that is cached for an object under certain conditions, such as when a change is detected to the object. In one embodiment, the decision metadata may be invalidated either when the object is modified, or as initiated by the metadata provider due to changes in policy. As will be described in more detail below with reference to  FIGS. 2A and 2B , a per identity table and a global current sequence number table may be maintained, and a sequence number for a provider from the per identity table may be compared with the provider&#39;s current sequence number from the global table to determine if the provider will be invoked to generate current metadata for the current identity. 
     FIG. 2A  is a diagram of a per identity table  200 A. As will be described in more detail below, the table  200 A illustrates how in a cache to go from the object ID to the decision metadata for a provider. As shown in  FIG. 2A , the per identity table  200 A includes a provider column  210 , a provider sequence number column  220 , and a provider decision metadata for the object column  230 . The provider column  210  lists various providers (e.g., provider  1 , provider  2 , provider  3 , etc.). The provider sequence number column  220  includes sequence numbers for each of the associated providers. The provider decision metadata for the object column  230  includes decision metadata. In one embodiment, the sequence numbers of the provider sequence number column  220  may be thought of as being comparable to time stamps, in that they are compared to sequence numbers from another table (see  FIG. 2B ), as will be described in more detail below. 
     FIG. 2B  is a diagram of a global current sequence number table  200 B. As shown in  FIG. 2B , the global current sequence number table  200 B includes a provider column  250  and a sequence number column  260 . The provider column  250  lists various providers (e.g., provider  1 , provider  2 , provider  3 , etc.), while the sequence number column  260  lists the current sequence numbers associated with each of the providers. As will be described in more detail below with reference to  FIG. 3 , a sequence number from the sequence number column  220  of  FIG. 2A  is compared with a current sequence number from the sequence number column  260  of  FIG. 2B  to determine if the provider will be invoked to generate current metadata for the current identity. 
     FIG. 3  is a flow diagram illustrative of a general routine  300  for obtaining valid decision metadata for an identity utilizing the tables of  FIGS. 2A and 2B . As shown in  FIG. 3 , at a block  310 , the sequence number for a provider&#39;s metadata is obtained from a per identity table (e.g., see per identity table  200 A of  FIG. 2A ). At a block  320 , a current sequence number for the provider is obtained from a global table (e.g., see global current sequence number table  200 B of  FIG. 2B ). 
   At a decision block  330 , a determination is made as to whether the sequence numbers match. If the sequence numbers match, then the routine continues to a block  360 , as will be described in more detail below. If the sequence numbers do not match, then the routine continues to a block  340 . At block  340 , the provider is invoked to generate current metadata for the current identity. At a block  350 , the generated metadata is cached and the provider metadata sequence number is updated in the per identity table. At the block  360 , the metadata is returned for the provider. 
     FIG. 4  is a flow diagram illustrative of a routine  400  for retrieving decision metadata for an object (e.g., an object may be a file, an executable, etc.). At a decision block  410 , a determination is made as to whether an identity is present for the object. If an identity is present, then the routine continues to a decision block  430 , as will be described in more detail below. If an identity is not present, then the routine continues to a block  420 , where an identity is computed. 
   At decision block  430 , a determination is made as to whether the decision metadata for the object is available. If the decision metadata is available, then the routine ends. If the decision metadata is not available, then the routine continues to a block  440 , where the policy engine is asked to provide the decision metadata for the identified object. 
     FIG. 5  is a flow diagram illustrative of a routine  500  for revocation of an identity associated with an object. At a block  510 , a filter registers to be notified of all writes, renames, truncations, moves, deletions, and any other relevant modifications. The filter can be implemented as a filter on file system operations, or use notifications (such as OpLocks) or other synchronous callback mechanisms to detect modification. At a block  520 , upon detecting a modification to a tagged object, the filter invalidates all identity cached with that object. 
   As will be described in more detail below with regard to  FIGS. 6A ,  6 B, and  7 , removable media and network volumes are notable since a malicious user may alter the object/file beyond the detection of the local system. Since an ordinary user may control a network volume, they may tamper with a network object/file after the tagging system stores the identity and the data. Similarly, with removable media, the user may remove the media and change the contents on a different operating system. As will be described in more detail below with regard to  FIGS. 6A ,  6 B, and  7 , a copy mechanism may be utilized as part of the identity process. 
     FIGS. 6A and 6B  are flow diagrams illustrative of routines  600 A and  600 B for associating identities with objects on removable media. As shown in  FIG. 6A , at a block  610 , an object is copied. (In another embodiment, the copy may be avoided if the system can securely store the cache ID and upon media insertion any existing cached identity and data are deleted for that media.) At a block  620 , the identity is computed. At a decision block  630 , a determination is made as to whether the system has notifications for media removal and media arrival (as well as across system reboots). If the system does not have such notifications, then the identity may not be cached and the routine continues to block  650 , as will be described in more detail below (in other words, the local copy may essentially be thrown out in that it will not have a cached identity and will have to be recopied and have the identity recomputed each time). If the system has such notifications, then the routine continues to block  640 , where the identification is cached. At the block  650 , the identification is returned. 
   It will be appreciated that other embodiments of this routine for untrusted media may also be envisioned, and that the general point is that the correctness of the system depends on reliable change notifications, which prompt the invalidation of the media&#39;s cache. A media removal notification is one example, a per-file change notification is another. In many systems, such reliable change notifications may be available. In cases where they are not, whether it is because the media doesn&#39;t support a removal notice or the file system doesn&#39;t support the necessary per-file changes, or in general if the file system is not trusted, the fall back is the “recomputed on every run” alternative described above where the ID is not cached and is recomputed each time. In general the “recomputed on every run” alternative will be slower, but may be preferred in cases where reliable change notifications are not available. 
     FIG. 6B  is a flow diagram illustrative of a routine  600 B for invalidating a removable media&#39;s cache. As shown in  FIG. 6B , at a block  670 , a notification of media removal (or change notification in some file systems) or reboot is received. At a block  680 , the media&#39;s cache is invalidated. 
     FIG. 7  is a flow diagram illustrative of a routine  700  for associating identities with objects on a network volume system. At a block  710 , an object and ID are copied. In another embodiment, only the object may be copied at the block  710 , however the copying of both the object and ID provides more of an atomic mechanism, and the ID is not used until a determination is made that the object and ID were not changed, as will be described in more detail below with respect to block  740 . At a decision block  720 , a determination is made as to whether the system is trusted. If the system is not trusted, then the routine continues to a block  760 , where the identity is computed. If the system is trusted, then the routine continues to a decision block  730 . At decision block  730 , a determination is made as to whether the object is trusted. If the object is not trusted, then the routine continues to the block  760  where the identity is computed. If the object is trusted, then the routine continues to a decision block  740 . At decision block  740 , a determination is made as to whether the object was changed during the copying. If the object and ID were changed, then the routine continues to block  760  where the identity is computed. If the object and ID were not changed during the copying, then the routine continues to a block  750 , where the identity is obtained from the trusted system. In some embodiments, an ID might not be present, in which case the system may also make a determination prior to block  750  whether an ID was provided, and if an ID was provided, then at block  750  the ID is used, while if an ID was not provided, then the routine would continue to block  760 . 
   With regard to the routine  700  for network volumes, it will be appreciated that in one embodiment a local copy does not need to be made for all network volumes. Instead, a local copy is only made for untrusted network volumes. If the remote machine is trusted, and if the remote machine is able to send reliable change notifications, then the system doesn&#39;t have to fall back to copying it locally and recomputing the identification every time. Instead, it may be treated like a file on a trusted local volume. 
     FIG. 8  is a flow diagram illustrative of a routine  800  for associating identities with objects in a multi-boot system. At a block  810 , the tagging system stores a unique identifier denoting the current executing operating system to uniquely denote which operating system is identified and the associated data for the object. At a block  820 , when the system accesses the stored data, the currently executing operating system identification gets checked against the stored operating system identification with the data, and if there is a mismatch of the operating system&#39;s identifications, then the system invalidates the stored identity and data and reevaluates/verifies the object&#39;s identity and stores the current data along with the current operating system identification. 
   While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.