Re: [Qemu-devel] [PATCH v2] vnc: disable VNC password authentication (security type 2) when in FIPS mode

[Alexander Graf]

On 02.05.2012, at 21:32, Paul Moore wrote:

> 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 mode.
> 
> This patch causes qemu to emit a syslog entry indicating that VNC password
> auth is disabled when it detects the host is running in FIPS mode, and
> unless a VNC password was specified on the command line it continues
> normally.  However, if a VNC password was given on the command line, qemu
> fails with an error message to stderr explaining that VNC password auth is
> not allowed in FIPS mode.

I just talked to Roman about this one and he had some comments :)


Alex

> 
> Signed-off-by: Paul Moore <address@hidden>
> 
> --
> Changelog
> * v2
> - Protected syslog with _WIN32
> - Protected the guts of fips_enabled() with __linux__
> - Converted fips_enabled() and the fips flag from int to bool
> *v1
> - Initial draft
> ---
> qemu-doc.texi |    8 +++++---
> ui/vnc.c      |   39 +++++++++++++++++++++++++++++++++++++++
> ui/vnc.h      |    1 +
> 3 files changed, 45 insertions(+), 3 deletions(-)
> 
> diff --git a/qemu-doc.texi b/qemu-doc.texi
> index e5d7ac4..f9b113e 100644
> --- a/qemu-doc.texi
> +++ b/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 [...OPTIONS...] -vnc :1,password -monitor stdio
> diff --git a/ui/vnc.c b/ui/vnc.c
> index deb9ecd..6162425 100644
> --- a/ui/vnc.c
> +++ b/ui/vnc.c
> @@ -32,6 +32,9 @@
> #include "acl.h"
> #include "qemu-objects.h"
> #include "qmp-commands.h"
> +#ifndef _WIN32
> +#include <syslog.h>
> +#endif
> 
> #define VNC_REFRESH_INTERVAL_BASE 30
> #define VNC_REFRESH_INTERVAL_INC  50
> @@ -48,6 +51,27 @@ static DisplayChangeListener *dcl;
> static int vnc_cursor_define(VncState *vs);
> static void vnc_release_modifiers(VncState *vs);
> 
> +static bool fips_enabled(void)
> +{
> +    bool enabled = false;
> +
> +#ifdef __linux__
> +    FILE *fds;
> +    char value;
> +
> +    fds = fopen("/proc/sys/crypto/fips_enabled", "r");
> +    if (fds == NULL) {
> +        return false;
> +    }
> +    if (fread(&value, sizeof(value), 1, fds) == 1 && value == '1') {
> +        enabled = true;
> +    }
> +    fclose(fds);
> +#endif /* __linux__ */
> +
> +    return enabled;
> +}
> +
> static void vnc_set_share_mode(VncState *vs, VncShareMode mode)
> {
> #ifdef _VNC_DEBUG
> @@ -2748,6 +2772,14 @@ void vnc_display_init(DisplayState *ds)
>     dcl->idle = 1;
>     vnc_display = vs;
> 
> +    vs->fips = fips_enabled();
> +    VNC_DEBUG("FIPS mode %s\n", (vs->fips ? "enabled" : "disabled"));
> +#ifndef _WIN32
> +    if (vs->fips) {
> +        syslog(LOG_NOTICE, "Disabling VNC password auth due to FIPS mode\n");
> +    }
> +#endif /* _WIN32 */
> +
>     vs->lsock = -1;
> 
>     vs->ds = ds;
> @@ -2892,6 +2924,13 @@ int vnc_display_open(DisplayState *ds, const char 
> *display)
>     while ((options = strchr(options, ','))) {
>         options++;
>         if (strncmp(options, "password", 8) == 0) {
> +            if (vs->fips) {
> +                fprintf(stderr,
> +                        "VNC password auth disabled due to FIPS mode\n");
> +                g_free(vs->display);
> +                vs->display = NULL;
> +                return -1;
> +            }
>             password = 1; /* Require password auth */
>         } else if (strncmp(options, "reverse", 7) == 0) {
>             reverse = 1;
> diff --git a/ui/vnc.h b/ui/vnc.h
> index a851ebd..d41631b 100644
> --- a/ui/vnc.h
> +++ b/ui/vnc.h
> @@ -160,6 +160,7 @@ struct VncDisplay
>     char *display;
>     char *password;
>     time_t expires;
> +    bool fips;
>     int auth;
>     bool lossy;
>     bool non_adaptive;
> 
>