unix: add bindings for keyutils syscalls

This CL adds support for the ADD_KEY, REQUESET_KEY, and KEYCTL syscalls.
These syscalls allow access to the kernel keyring facilities. In C code,
these syscalls are wrapped by the libkeyutils package. See:
	http://man7.org/linux/man-pages/man7/keyutils.7.html

The ADD_KEY and REQUEST_KEY calls are fairly straightforward, but the
KEYCTL syscall is a multiplexor for a number of key management
functions. See:
	http://man7.org/linux/man-pages/man3/keyctl.3.html

The Go bindings for the KEYCTL functions attempt to replicate what
libkeyutils does. This is done via generated helper functions.

Change-Id: If8c97d4ef5bce14c43dee3e6772ded42dc3c595a
Reviewed-on: https://go-review.googlesource.com/41415
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/syscall_linux.go

@@ -755,6 +755,113 @@ func SetsockoptIPMreqn(fd, level, opt int, mreq *IPMreqn) (err error) {
 	return setsockopt(fd, level, opt, unsafe.Pointer(mreq), unsafe.Sizeof(*mreq))
 }
 
+// Keyctl Commands (http://man7.org/linux/man-pages/man2/keyctl.2.html)
+
+// KeyctlInt calls keyctl commands in which each argument is an int.
+// These commands are KEYCTL_REVOKE, KEYCTL_CHOWN, KEYCTL_CLEAR, KEYCTL_LINK,
+// KEYCTL_UNLINK, KEYCTL_NEGATE, KEYCTL_SET_REQKEY_KEYRING, KEYCTL_SET_TIMEOUT,
+// KEYCTL_ASSUME_AUTHORITY, KEYCTL_SESSION_TO_PARENT, KEYCTL_REJECT,
+// KEYCTL_INVALIDATE, and KEYCTL_GET_PERSISTENT.
+//sys	KeyctlInt(cmd int, arg2 int, arg3 int, arg4 int, arg5 int) (ret int, err error) = SYS_KEYCTL
+
+// KeyctlBuffer calls keyctl commands in which the third and fourth
+// arguments are a buffer and its length, respectively.
+// These commands are KEYCTL_UPDATE, KEYCTL_READ, and KEYCTL_INSTANTIATE.
+//sys	KeyctlBuffer(cmd int, arg2 int, buf []byte, arg5 int) (ret int, err error) = SYS_KEYCTL
+
+// KeyctlString calls keyctl commands which return a string.
+// These commands are KEYCTL_DESCRIBE and KEYCTL_GET_SECURITY.
+func KeyctlString(cmd int, id int) (string, error) {
+	// We must loop as the string data may change in between the syscalls.
+	// We could allocate a large buffer here to reduce the chance that the
+	// syscall needs to be called twice; however, this is unnecessary as
+	// the performance loss is negligible.
+	var buffer []byte
+	for {
+		// Try to fill the buffer with data
+		length, err := KeyctlBuffer(cmd, id, buffer, 0)
+		if err != nil {
+			return "", err
+		}
+
+		// Check if the data was written
+		if length <= len(buffer) {
+			// Exclude the null terminator
+			return string(buffer[:length-1]), nil
+		}
+
+		// Make a bigger buffer if needed
+		buffer = make([]byte, length)
+	}
+}
+
+// Keyctl commands with special signatures.
+
+// KeyctlGetKeyringID implements the KEYCTL_GET_KEYRING_ID command.
+// See the full documentation at:
+// http://man7.org/linux/man-pages/man3/keyctl_get_keyring_ID.3.html
+func KeyctlGetKeyringID(id int, create bool) (ringid int, err error) {
+	createInt := 0
+	if create {
+		createInt = 1
+	}
+	return KeyctlInt(KEYCTL_GET_KEYRING_ID, id, createInt, 0, 0)
+}
+
+// KeyctlSetperm implements the KEYCTL_SETPERM command. The perm value is the
+// key handle permission mask as described in the "keyctl setperm" section of
+// http://man7.org/linux/man-pages/man1/keyctl.1.html.
+// See the full documentation at:
+// http://man7.org/linux/man-pages/man3/keyctl_setperm.3.html
+func KeyctlSetperm(id int, perm uint32) error {
+	_, err := KeyctlInt(KEYCTL_SETPERM, id, int(perm), 0, 0)
+	return err
+}
+
+//sys	keyctlJoin(cmd int, arg2 string) (ret int, err error) = SYS_KEYCTL
+
+// KeyctlJoinSessionKeyring implements the KEYCTL_JOIN_SESSION_KEYRING command.
+// See the full documentation at:
+// http://man7.org/linux/man-pages/man3/keyctl_join_session_keyring.3.html
+func KeyctlJoinSessionKeyring(name string) (ringid int, err error) {
+	return keyctlJoin(KEYCTL_JOIN_SESSION_KEYRING, name)
+}
+
+//sys	keyctlSearch(cmd int, arg2 int, arg3 string, arg4 string, arg5 int) (ret int, err error) = SYS_KEYCTL
+
+// KeyctlSearch implements the KEYCTL_SEARCH command.
+// See the full documentation at:
+// http://man7.org/linux/man-pages/man3/keyctl_search.3.html
+func KeyctlSearch(ringid int, keyType, description string, destRingid int) (id int, err error) {
+	return keyctlSearch(KEYCTL_SEARCH, ringid, keyType, description, destRingid)
+}
+
+//sys	keyctlIOV(cmd int, arg2 int, payload []Iovec, arg5 int) (err error) = SYS_KEYCTL
+
+// KeyctlInstantiateIOV implements the KEYCTL_INSTANTIATE_IOV command. This
+// command is similar to KEYCTL_INSTANTIATE, except that the payload is a slice
+// of Iovec (each of which represents a buffer) instead of a single buffer.
+// See the full documentation at:
+// http://man7.org/linux/man-pages/man3/keyctl_instantiate_iov.3.html
+func KeyctlInstantiateIOV(id int, payload []Iovec, ringid int) error {
+	return keyctlIOV(KEYCTL_INSTANTIATE_IOV, id, payload, ringid)
+}
+
+//sys	keyctlDH(cmd int, arg2 *KeyctlDHParams, buf []byte) (ret int, err error) = SYS_KEYCTL
+
+// KeyctlDHCompute implements the KEYCTL_DH_COMPUTE command. This command
+// computes a Diffie-Hellman shared secret based on the provide params. The
+// secret is written to the provided buffer and the returned size is the number
+// of bytes written (returning an error if there is insufficient space in the
+// buffer). If a nil buffer is passed in, this function returns the minimum
+// buffer length needed to store the appropriate data. Note that this differs
+// from KEYCTL_READ's behavior which always returns the requested payload size.
+// See the full documentation at:
+// http://man7.org/linux/man-pages/man3/keyctl_dh_compute.3.html
+func KeyctlDHCompute(params *KeyctlDHParams, buffer []byte) (size int, err error) {
+	return keyctlDH(KEYCTL_DH_COMPUTE, params, buffer)
+}
+
 func Recvmsg(fd int, p, oob []byte, flags int) (n, oobn int, recvflags int, from Sockaddr, err error) {
 	var msg Msghdr
 	var rsa RawSockaddrAny
@@ -1033,6 +1140,7 @@ func Mount(source string, target string, fstype string, flags uintptr, data stri
  * Direct access
  */
 //sys	Acct(path string) (err error)
+//sys	AddKey(keyType string, description string, payload []byte, ringid int) (id int, err error)
 //sys	Adjtimex(buf *Timex) (state int, err error)
 //sys	Chdir(path string) (err error)
 //sys	Chroot(path string) (err error)
@@ -1086,6 +1194,7 @@ func Getpgrp() (pid int) {
 //sys	read(fd int, p []byte) (n int, err error)
 //sys	Removexattr(path string, attr string) (err error)
 //sys	Renameat(olddirfd int, oldpath string, newdirfd int, newpath string) (err error)
+//sys	RequestKey(keyType string, description string, callback string, destRingid int) (id int, err error)
 //sys	Setdomainname(p []byte) (err error)
 //sys	Sethostname(p []byte) (err error)
 //sysnb	Setpgid(pid int, pgid int) (err error)
@@ -1169,7 +1278,6 @@ func Vmsplice(fd int, iovs []Iovec, flags int) (int, error) {
 /*
  * Unimplemented
  */
-// AddKey
 // AfsSyscall
 // Alarm
 // ArchPrctl
@@ -1208,7 +1316,6 @@ func Vmsplice(fd int, iovs []Iovec, flags int) (int, error) {
 // IoprioGet
 // IoprioSet
 // KexecLoad
-// Keyctl
 // Lgetxattr
 // Llistxattr
 // LookupDcookie
@@ -1244,7 +1351,6 @@ func Vmsplice(fd int, iovs []Iovec, flags int) (int, error) {
 // Readahead
 // Readv
 // RemapFilePages
-// RequestKey
 // RestartSyscall
 // RtSigaction
 // RtSigpending