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. Should be called only once during system startup. struct veriexec_file_entry *vfe veriexec_lookup(struct vnode *vp) Lookup private Veriexec data associated with vp. Returns NULL if file is not monitored by Veriexec. int veriexec_verify(struct lwp *l, struct vnode *vp, const u_char *name, int flag, boolean_t *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. void veriexec_report(const u_char *msg, u_char *name, struct lwp *l, int flags) Log a Veriexec message in msg for file name. l is optionally the LWP context in question. flags control how the message will be formatted, where will it be logged to, and whether the system should panic after posting it. Flags can be binary-OR'd together. Available flags include: REPORT_ALWAYS The message should always be printed. This is a synonym for 0. REPORT_VERBOSE The message should be printed only if Veriexec is in verbose mode. REPORT_DEBUG The message should be printed only if Veriexec is in debug verbosity. REPORT_ALARM The message is an alarm. If l is not NULL, user and process ids will be printed. The log will be sent to the LOG_ALERT syslog facility. REPORT_PANIC The system should panic(9) after posting the mes- sage. 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_table_add(struct lwp *l, prop_dictionary_t dict) Prepare storage for a Veriexec table, to optimize the lookup time. dict holds the following elements: Name TypePurpose mount stringmount-point count uint64estimated number of entries 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 access flags above) fp-type string fingerprint hashing algorithm fp data the fingerprint int veriexec_table_delete(struct mount *mp) Remove Veriexec table for mount-point mp. int veriexec_file_delete(struct vnode *vp) Remove Veriexec entry for vp. Hook Handlers int veriexec_renamechk(struct vnode *fromvp, const char *fromname, struct vnode *tovp, const char *toname, struct lwp *l) 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 vnode *vp, const char *name, struct lwp *l) 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 (see above) 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. 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), 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 commited 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 4.0 December 1, 2006 NetBSD 4.0