VERIEXEC(9)            NetBSD Kernel Developer's Manual            VERIEXEC(9)

NAME
     veriexec -- in-kernel file integrity subsystem KPI

SYNOPSIS
     #include <sys/verified_exec.h>

DESCRIPTION
     veriexec is the KPI for Veriexec, the NetBSD in-kernel file integrity
     subsystem.  It is responsible for managing the supported hashing algo-
     rithms, fingerprint calculation and comparison, file monitoring tables,
     and relevant hooks to enforce the Veriexec policy.

   Core Routines
     void veriexec_init(void)
               Initialize the Veriexec subsystem.  Called only once during
               system startup.

     bool veriexec_lookup(struct vnode *vp)
               Check if vp is monitored by Veriexec or not.  Returns true if
               it is, or false otherwise.

     int veriexec_verify(struct lwp *l, struct vnode *vp, const u_char *name,
               int flag, bool *found)
               Verifies the digital fingerprint of vp.  name is the filename,
               and flag is the access flag.  The access flag can be one of:

               VERIEXEC_DIRECT
                             The file was executed directly via execve(2).

               VERIEXEC_INDIRECT
                             The file was executed indirectly, either as an
                             interpreter for a script or mapped to an exe-
                             cutable memory region.

               VERIEXEC_FILE
                             The file was opened for reading/writing.

               l is the LWP for the request context.

               An optional argument, found, is a pointer to a boolean indicat-
               ing whether an entry for the file was found in the Veriexec
               tables.

     void veriexec_purge(struct vnode *vp)
               Purge the file entry for vp.  This invalidates the fingerprint
               so it will be evaluated next time the file is accessed.

   Fingerprint Related Routines
     veriexec_fpops_add(const char *fp_type, size_t hash_len, size_t ctx_size,
               veriexec_fpop_init_t init, veriexec_fpop_update_t update,
               veriexec_fpop_final_t final)
               Add support for fingerprinting algorithm fp_type with binary
               hash length hash_len and calculation context size ctx_size to
               Veriexec.  init, update, and final are the routines used to
               initialize, update, and finalize a calculation context.

   Table Management Routines
     int veriexec_file_add(struct lwp *l, prop_dictionary_t dict)
               Add a Veriexec entry for the file described by dict.

               dict is expected to have the following:

               Name          Type      Purpose
               file          string    filename
               entry-type    uint8     entry type flags (see veriexec(4))
               fp-type       string    fingerprint hashing algorithm
               fp            data      the fingerprint

     int veriexec_file_delete(struct lwp *l, struct vnode *vp)
               Remove Veriexec entry for vp.

     int veriexec_table_delete(struct lwp *l, struct mount *mp)
               Remove Veriexec table for mount-point mp.

     int veriexec_flush(struct lwp *l)
               Delete all Veriexec tables.

   Hook Handlers
     int veriexec_openchk(struct lwp *l, struct vnode *vp, const char *path,
               int fmode)
               Called when a file is opened.

               l is the LWP opening the file, vp is a vnode for the file being
               opened as returned from namei(9).  If NULL, the file is being
               created.  path is the pathname for the file (not necessarily a
               full path), and fmode are the mode bits with which the file was
               opened.

     int veriexec_renamechk(struct lwp *l, struct vnode *fromvp, const char
               *fromname, struct vnode *tovp, const char *toname)
               Called when a file is renamed.

               fromvp and fromname are the vnode and filename of the file
               being renamed.  tovp and toname are the vnode and filename of
               the target file.  l is the LWP renaming the file.

               Depending on the strict level, veriexec will either track
               changes appropriately or prevent the rename.

     int veriexec_removechk(struct lwp *l, struct vnode *vp, const char *name)
               Called when a file is removed.

               vp is the vnode of the file being removed, and name is the
               filename.  l is the LWP removing the file,

               Depending on the strict level, veriexec will either clean-up
               after the file or prevent its removal.

     int veriexec_unmountchk(struct mount *mp)
               Checks if the current strict level allows mp to be unmounted.

   Misc. Routines
     int veriexec_convert(struct vnode *vp, prop_dictionary_t rdict)
               Convert Veriexec entry for vp to human-readable proplib(3) dic-
               tionary, rdict, with the following elements:

               Name          Type      Purpose
               entry-type    uint8     entry type flags (see veriexec(4))
               status        uint8     entry status (see below)
               fp-type       string    fingerprint hashing algorithm
               fp            data      the fingerprint

               The ``status'' can be one of the following:

               Status                  Meaning
               FINGERPRINT_NOTEVAL     not evaluated
               FINGERPRINT_VALID       fingerprint match
               FINGERPRINT_MISMATCH    fingerprint mismatch

               If no entry was found, ENOENT is returned.  Otherwise, zero.

     int veriexec_dump(struct lwp *l, prop_array_t rarray)
               Fill rarray with entries for all files monitored by Veriexec
               that have a filename associated with them.

               Each element in rarray is a dictionary with the same elements
               as filled by veriexec_convert(), with an additional field,
               ``file'', containing the filename.

FILES
     Path                                Purpose
     src/sys/dev/verified_exec.c         driver for userland communication
     src/sys/sys/verified_exec.h         shared (userland/kernel) header file
     src/sys/kern/kern_verifiedexec.c    subsystem code
     src/sys/kern/vfs_syscalls.c         rename, remove, and unmount policies
     src/sys/kern/vfs_vnops.c            regular file access policy

SEE ALSO
     proplib(3), sysctl(3), veriexec(4), security(8), sysctl(8),
     veriexecctl(8), veriexecgen(8), fileassoc(9)

AUTHORS
     Brett Lymn <blymn@NetBSD.org>
     Elad Efrat <elad@NetBSD.org>

CAVEATS
     There are two known issues with Veriexec that should be considered when
     using it.

   Remote File-systems
     There is an issue providing protection for files residing on mounts from
     remote hosts.  Because access to the file-system does not necessarily go
     through veriexec, there is no way to track on-disk changes.  While it is
     possible to minimize the effect by evaluating the file's fingerprint on
     each access without caching the result, a problem arises when a file is
     overwritten after its fingerprint has been evaluated and it is running on
     the local host.

     An attacker could potentially overwrite the file contents in the remote
     host at that point, and force a flush on the local host, resulting in
     paging in of the files from the disk, introducing malicious code into a
     supposedly safe address space.

     There is a fix for this issue, however due to dependencies on other work
     that is still in progress it has not been committed yet.

   Layered File-systems
     Due to VFS limitations, veriexec cannot track the same on-disk file
     across multiple layers of overlay file-systems.  Therefore, you cannot
     expect changes to files on overlay mounts will be detected simply because
     the underlying mount is monitored by veriexec.

     A workaround for this issue is listing all files, under all mounts, you
     want monitored in the signature file.

NetBSD 5.0_STABLE              February 10, 2008             NetBSD 5.0_STABLE
