vnc: disable VNC password authentication (security type 2) when in FIPS mode

FIPS 140-2 requires disabling certain ciphers, including DES, which is used
by VNC to obscure passwords when they are sent over the network.  The
solution for FIPS users is to disable the use of VNC password auth when the
host system is operating in FIPS compliance mode and the user has specified
'-enable-fips' on the QEMU command line.

This patch causes QEMU to emit a message to stderr when the host system is
running in FIPS mode and a VNC password was specified on the commend line.
If the system is not running in FIPS mode, or is running in FIPS mode but
VNC password authentication was not requested, QEMU operates normally.

Signed-off-by: Paul Moore <pmoore@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

osdep.c

@@ -24,6 +24,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <stdarg.h>
+#include <stdbool.h>
 #include <string.h>
 #include <errno.h>
 #include <unistd.h>
@@ -48,6 +49,8 @@ extern int madvise(caddr_t, size_t, int);
 #include "trace.h"
 #include "qemu_socket.h"
 
+static bool fips_enabled = false;
+
 static const char *qemu_version = QEMU_VERSION;
 
 int socket_set_cork(int fd, int v)
@@ -253,3 +256,29 @@ const char *qemu_get_version(void)
 {
     return qemu_version;
 }
+
+void fips_set_state(bool requested)
+{
+#ifdef __linux__
+    if (requested) {
+        FILE *fds = fopen("/proc/sys/crypto/fips_enabled", "r");
+        if (fds != NULL) {
+            fips_enabled = (fgetc(fds) == '1');
+            fclose(fds);
+        }
+    }
+#else
+    fips_enabled = false;
+#endif /* __linux__ */
+
+#ifdef _FIPS_DEBUG
+    fprintf(stderr, "FIPS mode %s (requested %s)\n",
+	    (fips_enabled ? "enabled" : "disabled"),
+	    (requested ? "enabled" : "disabled"));
+#endif
+}
+
+bool fips_get_state(void)
+{
+    return fips_enabled;
+}

osdep.h

@@ -3,6 +3,7 @@
 
 #include <stdarg.h>
 #include <stddef.h>
+#include <stdbool.h>
 #ifdef __OpenBSD__
 #include <sys/types.h>
 #include <sys/signal.h>
@@ -154,4 +155,7 @@ void qemu_set_cloexec(int fd);
 void qemu_set_version(const char *);
 const char *qemu_get_version(void);
 
+void fips_set_state(bool requested);
+bool fips_get_state(void);
+
 #endif

qemu-doc.texi

@@ -1124,9 +1124,11 @@ the protocol limits passwords to 8 characters it should not be considered
 to provide high security. The password can be fairly easily brute-forced by
 a client making repeat connections. For this reason, a VNC server using password
 authentication should be restricted to only listen on the loopback interface
-or UNIX domain sockets. Password authentication is requested with the @code{password}
-option, and then once QEMU is running the password is set with the monitor. Until
-the monitor is used to set the password all clients will be rejected.
+or UNIX domain sockets. Password authentication is not supported when operating
+in FIPS 140-2 compliance mode as it requires the use of the DES cipher. Password
+authentication is requested with the @code{password} option, and then once QEMU
+is running the password is set with the monitor. Until the monitor is used to
+set the password all clients will be rejected.
 
 @example
 qemu-system-i386 [...OPTIONS...] -vnc :1,password -monitor stdio

qemu-options.hx

@@ -2787,6 +2787,17 @@ DEF("qtest-log", HAS_ARG, QEMU_OPTION_qtest_log,
     "-qtest-log LOG  specify tracing options\n",
     QEMU_ARCH_ALL)
 
+#ifdef __linux__
+DEF("enable-fips", 0, QEMU_OPTION_enablefips,
+    "-enable-fips    enable FIPS 140-2 compliance\n",
+    QEMU_ARCH_ALL)
+#endif
+STEXI
+@item -enable-fips
+@findex -enable-fips
+Enable FIPS 140-2 compliance mode.
+ETEXI
+
 HXCOMM This is the last statement. Insert new options before this line!
 STEXI
 @end table

ui/vnc.c

@@ -32,6 +32,7 @@
 #include "acl.h"
 #include "qemu-objects.h"
 #include "qmp-commands.h"
+#include "osdep.h"
 
 #define VNC_REFRESH_INTERVAL_BASE 30
 #define VNC_REFRESH_INTERVAL_INC  50
@@ -2875,6 +2876,15 @@ int vnc_display_open(DisplayState *ds, const char *display)
     while ((options = strchr(options, ','))) {
         options++;
         if (strncmp(options, "password", 8) == 0) {
+            if (fips_get_state()) {
+                fprintf(stderr,
+                        "VNC password auth disabled due to FIPS mode, "
+                        "consider using the VeNCrypt or SASL authentication "
+                        "methods as an alternative\n");
+                g_free(vs->display);
+                vs->display = NULL;
+                return -1;
+            }
             password = 1; /* Require password auth */
         } else if (strncmp(options, "reverse", 7) == 0) {
             reverse = 1;

vl.c

@@ -159,6 +159,7 @@ int main(int argc, char **argv)
 #include "qemu-queue.h"
 #include "cpus.h"
 #include "arch_init.h"
+#include "osdep.h"
 
 #include "ui/qemu-spice.h"
 
@@ -3198,6 +3199,9 @@ int main(int argc, char **argv, char **envp)
             case QEMU_OPTION_qtest_log:
                 qtest_log = optarg;
                 break;
+            case QEMU_OPTION_enablefips:
+                fips_set_state(true);
+                break;
             default:
                 os_parse_cmd_args(popt->index, optarg);
             }