[PATCH 02/18] usbip: Add support for client authentication

From: Maximilian Eschenbacher
Date: Tue Sep 16 2014 - 18:11:39 EST

From: Dominik Paulus <dominik.paulus@xxxxxx>

This patch adds support for authenticating both client and server using
a pre-shared passphrase using SRP (Secure Remote Password) over TLS (see
RFC 5054) using GnuTLS. Both usbip and usbipd now accept a shared secret
as a command line argument. Currently, the established TLS connection is
only used to perform a secure handshake and dropped before the socket is
passed to the kernel. The code may be extended to exchange a session key
over TLS and pass it to the kernel to perform IPsec.

Signed-off-by: Maximilian Eschenbacher <maximilian@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Fjodor Schelichow <fjodor.schelichow@xxxxxxxxxxx>
Signed-off-by: Johannes Stadlinger <johannes.stadlinger@xxxxxx>
Signed-off-by: Dominik Paulus <dominik.paulus@xxxxxx>
Signed-off-by: Tobias Polzer <tobias.polzer@xxxxxx>
---
tools/usb/usbip/configure.ac | 14 +++
tools/usb/usbip/doc/usbip.8 | 4 +
tools/usb/usbip/doc/usbipd.8 | 5 +
tools/usb/usbip/src/usbip.c | 30 +++++-
tools/usb/usbip/src/usbip_attach.c | 2 +-
tools/usb/usbip/src/usbip_list.c | 2 +-
tools/usb/usbip/src/usbip_network.c | 185 ++++++++++++++++++++++++++++++++++++
tools/usb/usbip/src/usbip_network.h | 11 ++-
tools/usb/usbip/src/usbipd.c | 115 ++++++++++++++++------
9 files changed, 335 insertions(+), 33 deletions(-)

diff --git a/tools/usb/usbip/configure.ac b/tools/usb/usbip/configure.ac
index 607d05c..6a8156f 100644
--- a/tools/usb/usbip/configure.ac
+++ b/tools/usb/usbip/configure.ac
@@ -83,6 +83,20 @@ AC_ARG_WITH([tcp-wrappers],
AC_DEFINE([HAVE_LIBWRAP], [1], [use tcp wrapper])],
[AC_MSG_RESULT([no]); LIBS="$saved_LIBS"])])

+# Checks for the GnuTLS library
+AC_ARG_WITH([gnutls],
+ [AS_HELP_STRING([--with-gnutls],
+ [use the GnuTLS library for authentication])],
+ dnl [ACTION-IF-GIVEN]
+ [if test "$withval" = "yes"; then
+ PKG_CHECK_MODULES([GNUTLS], [gnutls])
+ AC_DEFINE([HAVE_GNUTLS], [1], [use gnutls])
+ CFLAGS="$CFLAGS $GNUTLS_CFLAGS"
+ LDFLAGS="$LDFLAGS $GNUTLS_LIBS"
+ fi
+ ],
+ )
+
# Sets directory containing usb.ids.
AC_ARG_WITH([usbids-dir],
[AS_HELP_STRING([--with-usbids-dir=DIR],
diff --git a/tools/usb/usbip/doc/usbip.8 b/tools/usb/usbip/doc/usbip.8
index a6097be..847aa40 100644
--- a/tools/usb/usbip/doc/usbip.8
+++ b/tools/usb/usbip/doc/usbip.8
@@ -27,6 +27,10 @@ Log to syslog.
\fB\-\-tcp-port PORT\fR
.IP
Connect to PORT on remote host (used for attach and list --remote).
+
+\fB\-\-auth\fR
+.IP
+Set the password to be used for client authentication. See usbipd(8) for more information.
.PP

.SH COMMANDS
diff --git a/tools/usb/usbip/doc/usbipd.8 b/tools/usb/usbip/doc/usbipd.8
index ac4635d..8beb95a 100644
--- a/tools/usb/usbip/doc/usbipd.8
+++ b/tools/usb/usbip/doc/usbipd.8
@@ -52,6 +52,11 @@ If no FILE specified, use /var/run/usbipd.pid
\fB\-tPORT\fR, \fB\-\-tcp\-port PORT\fR
.IP
Listen on TCP/IP port PORT.
+
+.HP
+\fB\-s\fR, \fB\-\-auth\fR
+.IP
+Sets the password to be used for client authentication. If -a is used, the server will only accept connections from authenticated clients. Note: USB traffic will still be unencrypted, this currently only serves for authentication.
.PP

\fB\-h\fR, \fB\-\-help\fR
diff --git a/tools/usb/usbip/src/usbip.c b/tools/usb/usbip/src/usbip.c
index d7599d9..cd7e420 100644
--- a/tools/usb/usbip/src/usbip.c
+++ b/tools/usb/usbip/src/usbip.c
@@ -25,6 +25,12 @@
#include <getopt.h>
#include <syslog.h>

+#include "../config.h"
+
+#ifdef HAVE_GNUTLS
+#include <gnutls/gnutls.h>
+#endif
+
#include "usbip_common.h"
#include "usbip_network.h"
#include "usbip.h"
@@ -35,8 +41,12 @@ static int usbip_version(int argc, char *argv[]);
static const char usbip_version_string[] = PACKAGE_STRING;

static const char usbip_usage_string[] =
- "usbip [--debug] [--log] [--tcp-port PORT] [version]\n"
- " [help] <command> <args>\n";
+ "usbip "
+#ifdef HAVE_GNUTLS
+ "[--auth PASSWORD] "
+#endif
+ "[--debug] [--log] [--tcp-port PORT]\n"
+ " [version] [help] <command> <args>\n";

static void usbip_usage(void)
{
@@ -148,6 +158,7 @@ int main(int argc, char *argv[])
{ "debug", no_argument, NULL, 'd' },
{ "log", no_argument, NULL, 'l' },
{ "tcp-port", required_argument, NULL, 't' },
+ { "auth", required_argument, NULL, 's' },
{ NULL, 0, NULL, 0 }
};

@@ -158,12 +169,25 @@ int main(int argc, char *argv[])
usbip_use_stderr = 1;
opterr = 0;
for (;;) {
- opt = getopt_long(argc, argv, "+dlt:", opts, NULL);
+ opt = getopt_long(argc, argv, "+dls:t:", opts, NULL);

if (opt == -1)
break;

switch (opt) {
+ case 's':
+#ifdef HAVE_GNUTLS
+ usbip_srp_password = optarg;
+ rc = gnutls_global_init();
+ if (rc < 0) {
+ err("Unable to initialize GnuTLS library: %s",
+ gnutls_strerror(rc));
+ return EXIT_FAILURE;
+ }
+#else
+ err("usbip has been compiled without GnuTLS support");
+#endif
+ break;
case 'd':
usbip_use_debug = 1;
break;
diff --git a/tools/usb/usbip/src/usbip_attach.c b/tools/usb/usbip/src/usbip_attach.c
index d58a14d..4421ebc 100644
--- a/tools/usb/usbip/src/usbip_attach.c
+++ b/tools/usb/usbip/src/usbip_attach.c
@@ -175,7 +175,7 @@ static int attach_device(char *host, char *busid)
int rc;
int rhport;

- sockfd = usbip_net_tcp_connect(host, usbip_port_string);
+ sockfd = usbip_net_connect(host);
if (sockfd < 0) {
err("tcp connect");
return -1;
diff --git a/tools/usb/usbip/src/usbip_list.c b/tools/usb/usbip/src/usbip_list.c
index d5ce34a..6042b7e 100644
--- a/tools/usb/usbip/src/usbip_list.c
+++ b/tools/usb/usbip/src/usbip_list.c
@@ -132,7 +132,7 @@ static int list_exported_devices(char *host)
int rc;
int sockfd;

- sockfd = usbip_net_tcp_connect(host, usbip_port_string);
+ sockfd = usbip_net_connect(host);
if (sockfd < 0) {
err("could not connect to %s:%s: %s", host,
usbip_port_string, gai_strerror(sockfd));
diff --git a/tools/usb/usbip/src/usbip_network.c b/tools/usb/usbip/src/usbip_network.c
index b4c37e7..6b8f949 100644
--- a/tools/usb/usbip/src/usbip_network.c
+++ b/tools/usb/usbip/src/usbip_network.c
@@ -29,11 +29,20 @@
#include <tcpd.h>
#endif

+#include "../config.h"
+#ifdef HAVE_GNUTLS
+#include <gnutls/gnutls.h>
+#include <gnutls/crypto.h>
+#endif
+
#include "usbip_common.h"
#include "usbip_network.h"

int usbip_port = 3240;
char *usbip_port_string = "3240";
+#ifdef HAVE_GNUTLS
+char *usbip_srp_password;
+#endif

void usbip_setup_port_number(char *arg)
{
@@ -301,3 +310,179 @@ int usbip_net_tcp_connect(char *hostname, char *service)

return sockfd;
}
+
+#ifdef HAVE_GNUTLS
+static gnutls_datum_t usbip_net_srp_salt, usbip_net_srp_verifier;
+static gnutls_srp_server_credentials_t usbip_net_srp_cred;
+
+#define SRP_GROUP gnutls_srp_2048_group_generator
+#define SRP_PRIME gnutls_srp_2048_group_prime
+
+int usbip_net_srp_client_handshake(int sockfd)
+{
+ int ret;
+ gnutls_session_t session;
+ gnutls_srp_client_credentials_t usbip_net_srp_cred;
+
+ ret = gnutls_srp_allocate_client_credentials(&usbip_net_srp_cred);
+ if (ret < 0)
+ return ret;
+
+ gnutls_srp_set_client_credentials(usbip_net_srp_cred, "dummyuser",
+ usbip_srp_password);
+
+ ret = gnutls_init(&session, GNUTLS_CLIENT);
+ if (ret < 0) {
+ gnutls_srp_free_client_credentials(usbip_net_srp_cred);
+ return ret;
+ }
+
+ gnutls_priority_set_direct(session, "NORMAL:+SRP", NULL);
+
+ gnutls_credentials_set(session, GNUTLS_CRD_SRP, usbip_net_srp_cred);
+ gnutls_transport_set_int (session, sockfd);
+
+ do {
+ ret = gnutls_handshake(session);
+ } while (ret < 0 && !gnutls_error_is_fatal(ret));
+
+ gnutls_bye(session, GNUTLS_SHUT_RDWR);
+
+ gnutls_deinit(session);
+ gnutls_srp_free_client_credentials(usbip_net_srp_cred);
+
+ return ret;
+}
+
+int net_srp_server_handshake(int connfd)
+{
+ int ret;
+ gnutls_session_t session;
+
+ if (gnutls_init(&session, GNUTLS_SERVER) != 0)
+ return -1;
+ gnutls_priority_set_direct(session, "NORMAL:-KX-ALL:+SRP", NULL);
+ ret = gnutls_credentials_set(session, GNUTLS_CRD_SRP,
+ usbip_net_srp_cred);
+ if (!ret)
+ return -1;
+
+ gnutls_transport_set_int(session, connfd);
+
+ do {
+ ret = gnutls_handshake(session);
+ } while (ret < 0 && gnutls_error_is_fatal(ret) == 0);
+
+ if (ret < 0)
+ err("GnuTLS handshake failed (%s)", gnutls_strerror(ret));
+ else
+ info("GnuTLS handshake completed");
+
+ if (gnutls_bye(session, GNUTLS_SHUT_RDWR) != 0)
+ err("Unable to shutdown TLS connection.");
+ gnutls_deinit(session);
+
+ return ret;
+}
+
+static int net_srp_callback(gnutls_session_t sess, const char *username,
+ gnutls_datum_t *nsalt, gnutls_datum_t *nverifier, gnutls_datum_t *g,
+ gnutls_datum_t *n)
+{
+ /*
+ * GnuTLS expects us to allocate all data returned from callbacks
+ * using gnutls_malloc(), thus, we have to create a fresh copy of
+ * our static credentials for every connection.
+ */
+ nsalt->data = gnutls_malloc(usbip_net_srp_salt.size);
+ nverifier->data = gnutls_malloc(usbip_net_srp_verifier.size);
+ if (nsalt->data == NULL || nverifier->data == NULL) {
+ gnutls_free(nsalt->data);
+ gnutls_free(nverifier->data);
+ return -1;
+ }
+ nsalt->size = usbip_net_srp_salt.size;
+ nverifier->size = usbip_net_srp_verifier.size;
+ memcpy(nverifier->data, usbip_net_srp_verifier.data,
+ usbip_net_srp_verifier.size);
+ memcpy(nsalt->data, usbip_net_srp_salt.data, usbip_net_srp_salt.size);
+
+ *g = SRP_GROUP;
+ *n = SRP_PRIME;
+
+ /* We only have a single session, thus, ignore it */
+ (void) sess;
+
+ if (strcmp(username, "dummyuser"))
+ /* User invalid, stored dummy data in g and n. */
+ return 1;
+
+ return 0;
+}
+
+int usbip_net_init_gnutls(void)
+{
+ int ret;
+
+ gnutls_global_init();
+
+ usbip_net_srp_salt.data = gnutls_malloc(16);
+ if (!usbip_net_srp_salt.data)
+ return GNUTLS_E_MEMORY_ERROR;
+
+ ret = gnutls_rnd(GNUTLS_RND_NONCE, usbip_net_srp_salt.data, 16);
+ if (ret < 0)
+ return ret;
+ usbip_net_srp_salt.size = 16;
+
+ ret = gnutls_srp_allocate_server_credentials(&usbip_net_srp_cred);
+ if (ret < 0)
+ return ret;
+
+ ret = gnutls_srp_verifier("dummyuser", optarg, &usbip_net_srp_salt,
+ &SRP_GROUP, &SRP_PRIME,
+ &usbip_net_srp_verifier);
+ if (ret < 0)
+ return ret;
+
+ gnutls_srp_set_server_credentials_function(usbip_net_srp_cred,
+ net_srp_callback);
+
+ return GNUTLS_E_SUCCESS;
+}
+#endif
+
+/*
+ * Connect to the server. Performs the TCP connection attempt
+ * and - if necessary - the TLS handshake used for authentication.
+ */
+int usbip_net_connect(char *hostname)
+{
+ int sockfd;
+
+ sockfd = usbip_net_tcp_connect(hostname, usbip_port_string);
+ if (sockfd < 0)
+ return sockfd;
+
+#ifdef HAVE_GNUTLS
+ if (usbip_srp_password) {
+ int rc;
+
+ rc = usbip_net_send_op_common(sockfd, OP_REQ_STARTTLS, 0);
+ if (rc < 0) {
+ err("usbip_net_send_op_common failed");
+ return EAI_SYSTEM;
+ }
+
+ rc = usbip_net_srp_client_handshake(sockfd);
+ if (rc < 0) {
+ err("Unable to perform TLS handshake (wrong password?): %s",
+ gnutls_strerror(rc));
+ close(sockfd);
+ return EAI_SYSTEM;
+ }
+ }
+#endif
+
+ return sockfd;
+}
diff --git a/tools/usb/usbip/src/usbip_network.h b/tools/usb/usbip/src/usbip_network.h
index c1e875c..292d584 100644
--- a/tools/usb/usbip/src/usbip_network.h
+++ b/tools/usb/usbip/src/usbip_network.h
@@ -15,6 +15,7 @@

extern int usbip_port;
extern char *usbip_port_string;
+extern char *usbip_srp_password;
void usbip_setup_port_number(char *arg);

/* ---------------------------------------------------------------------- */
@@ -167,6 +168,12 @@ struct op_devlist_reply_extra {
usbip_net_pack_uint32_t(pack, &(reply)->ndev);\
} while (0)

+/* ---------------------------------------------------------------------- */
+/* Initiate encrypted connection. */
+#define OP_STARTTLS 0x06
+#define OP_REQ_STARTTLS (OP_REQUEST | OP_STARTTLS)
+#define OP_REP_STARTTLS (OP_REPLY | OP_STARTTLS)
+
void usbip_net_pack_uint32_t(int pack, uint32_t *num);
void usbip_net_pack_uint16_t(int pack, uint16_t *num);
void usbip_net_pack_usb_device(int pack, struct usbip_usb_device *udev);
@@ -180,6 +187,8 @@ int usbip_net_set_reuseaddr(int sockfd);
int usbip_net_set_nodelay(int sockfd);
int usbip_net_set_keepalive(int sockfd);
int usbip_net_set_v6only(int sockfd);
-int usbip_net_tcp_connect(char *hostname, char *port);
+int usbip_net_connect(char *hostname);
+int net_srp_server_handshake(int connfd);
+int usbip_net_init_gnutls(void);

#endif /* __USBIP_NETWORK_H */
diff --git a/tools/usb/usbip/src/usbipd.c b/tools/usb/usbip/src/usbipd.c
index 2f87f2d..23c15d7 100644
--- a/tools/usb/usbip/src/usbipd.c
+++ b/tools/usb/usbip/src/usbipd.c
@@ -36,6 +36,11 @@
#include <tcpd.h>
#endif

+#ifdef HAVE_GNUTLS
+#include <gnutls/gnutls.h>
+#include <gnutls/crypto.h>
+#endif
+
#include <getopt.h>
#include <signal.h>
#include <poll.h>
@@ -64,6 +69,11 @@ static const char usbipd_help_string[] =
" -6, --ipv6\n"
" Bind to IPv6. Default is both.\n"
"\n"
+#ifdef HAVE_GNUTLS
+ " -sPASSWORD, --auth PASSWORD\n"
+ " Set PASSWORD as key used for authentication.\n"
+ "\n"
+#endif
" -D, --daemon\n"
" Run as a daemon process.\n"
"\n"
@@ -83,6 +93,8 @@ static const char usbipd_help_string[] =
" -v, --version\n"
" Show version.\n";

+static int need_auth;
+
static void usbipd_help(void)
{
printf("%s\n", usbipd_help_string);
@@ -239,14 +251,7 @@ static int recv_request_devlist(int connfd)

static int recv_pdu(int connfd)
{
- uint16_t code = OP_UNSPEC;
- int ret;
-
- ret = usbip_net_recv_op_common(connfd, &code);
- if (ret < 0) {
- dbg("could not receive opcode: %#0x", code);
- return -1;
- }
+ int auth = !need_auth, cont = 1, ret;

ret = usbip_host_refresh_device_list();
if (ret < 0) {
@@ -254,25 +259,63 @@ static int recv_pdu(int connfd)
return -1;
}

- info("received request: %#0x(%d)", code, connfd);
- switch (code) {
- case OP_REQ_DEVLIST:
- ret = recv_request_devlist(connfd);
- break;
- case OP_REQ_IMPORT:
- ret = recv_request_import(connfd);
- break;
- case OP_REQ_DEVINFO:
- case OP_REQ_CRYPKEY:
- default:
- err("received an unknown opcode: %#0x", code);
- ret = -1;
- }
+ /*
+ * Process opcodes. We might receive more than one, as the
+ * client might send STARTTLS first
+ */
+ while (cont) {
+ uint16_t code = OP_UNSPEC;

- if (ret == 0)
- info("request %#0x(%d): complete", code, connfd);
- else
- info("request %#0x(%d): failed", code, connfd);
+ ret = usbip_net_recv_op_common(connfd, &code);
+ if (ret < 0) {
+ dbg("could not receive opcode: %#0x", code);
+ return -1;
+ }
+
+ info("received request: %#0x(%d)", code, connfd);
+
+ /* We require an authenticated encryption */
+ if (!auth && code != OP_REQ_STARTTLS) {
+ usbip_net_send_op_common(connfd, OP_REPLY, ST_NA);
+ return -1;
+ }
+
+ switch (code) {
+#ifdef HAVE_GNUTLS
+ case OP_REQ_STARTTLS:
+ if (!need_auth) {
+ ret = -1;
+ err("Unexpected TLS handshake attempt (client uses password, server doesn't)");
+ } else {
+ ret = net_srp_server_handshake(connfd);
+ if (ret != 0)
+ err("TLS handshake failed");
+ auth = 1;
+ }
+ break;
+#endif
+ case OP_REQ_DEVLIST:
+ ret = recv_request_devlist(connfd);
+ cont = 0;
+ break;
+ case OP_REQ_IMPORT:
+ ret = recv_request_import(connfd);
+ cont = 0;
+ break;
+ case OP_REQ_DEVINFO:
+ case OP_REQ_CRYPKEY:
+ default:
+ err("received an unknown opcode: %#0x", code);
+ ret = -1;
+ }
+
+ if (ret == 0)
+ info("request %#0x(%d): complete", code, connfd);
+ else {
+ info("request %#0x(%d): failed", code, connfd);
+ break;
+ }
+ }

return ret;
}
@@ -593,6 +636,7 @@ int main(int argc, char *argv[])
{ "tcp-port", required_argument, NULL, 't' },
{ "help", no_argument, NULL, 'h' },
{ "version", no_argument, NULL, 'v' },
+ { "auth", required_argument, NULL, 's' },
{ NULL, 0, NULL, 0 }
};

@@ -605,6 +649,9 @@ int main(int argc, char *argv[])
int daemonize = 0;
int ipv4 = 0, ipv6 = 0;
int opt, rc = -1;
+#ifdef HAVE_GNUTLS
+ int ret;
+#endif

pid_file = NULL;

@@ -616,7 +663,7 @@ int main(int argc, char *argv[])

cmd = cmd_standalone_mode;
for (;;) {
- opt = getopt_long(argc, argv, "46DdP::t:hv", longopts, NULL);
+ opt = getopt_long(argc, argv, "46s:DdP::t:hv", longopts, NULL);

if (opt == -1)
break;
@@ -628,6 +675,20 @@ int main(int argc, char *argv[])
case '6':
ipv6 = 1;
break;
+ case 's':
+#ifdef HAVE_GNUTLS
+ need_auth = 1;
+ ret = usbip_net_init_gnutls();
+ if (ret < 0) {
+ err("Unable to initialize GnuTLS: %s",
+ gnutls_strerror(ret));
+ return EXIT_FAILURE;
+ }
+ break;
+#else
+ err("usbipd has been compiled without GnuTLS support");
+ break;
+#endif
case 'D':
daemonize = 1;
break;
--
2.1.0

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