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Re: [libvirt] [PATCH] Add some basic sanity checking of certificates before use



On Fri, Jul 15, 2011 at 11:40:01 +0100, Daniel P. Berrange wrote:
> If the libvirt daemon or libvirt client is configured with bogus
> certificates, it is very unhelpful to only find out about this
> when a TLS connection is actually attempted. Not least because
> the error messages you get back for failures are incredibly
> obscure.
> 
> This adds some basic sanity checking of certificates at the
> time the virNetTLSContext object is created. This is at libvirt
> startup, or when creating a virNetClient instance.
> 
> This checks that the certificate expiry/start dates are valid
> and that the certificate is actually signed by the CA that is
> loaded.
> 
> * src/rpc/virnettlscontext.c: Add certificate sanity checks
> ---
>  src/rpc/virnettlscontext.c |  144 ++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 140 insertions(+), 4 deletions(-)
> 
> diff --git a/src/rpc/virnettlscontext.c b/src/rpc/virnettlscontext.c
> index 1120e1e..b778550 100644
> --- a/src/rpc/virnettlscontext.c
> +++ b/src/rpc/virnettlscontext.c
> @@ -67,6 +67,7 @@ struct _virNetTLSSession {
>  
>      bool handshakeComplete;
>  
> +    bool isServer;
>      char *hostname;
>      gnutls_session_t session;
>      virNetTLSSessionWriteFunc writeFunc;
> @@ -95,6 +96,131 @@ static void virNetTLSLog(int level, const char *str) {
>      VIR_DEBUG("%d %s", level, str);
>  }
>  
> +
> +static gnutls_x509_crt_t virNetTLSContextSanityCheckCert(bool isServer,
> +                                                         const char *certFile)
> +{
> +    gnutls_datum_t data;
> +    gnutls_x509_crt_t cert = NULL;
> +    char *buf = NULL;
> +    int ret = -1;
> +    time_t now;
> +
> +    if ((now = time(NULL)) == ((time_t)-1)) {
> +        virReportSystemError(errno, "%s",
> +                             _("cannot get current time"));
> +        goto cleanup;
> +    }
> +
> +    if (gnutls_x509_crt_init(&cert) < 0) {
> +        virNetError(VIR_ERR_SYSTEM_ERROR, "%s",
> +                    _("Unable to initialize certificate"));
> +        goto cleanup;
> +    }
> +
> +    if (virFileReadAll(certFile, (1<<16), &buf) < 0)
> +        goto cleanup;
> +
> +    data.data = (unsigned char *)buf;
> +    data.size = strlen(buf);
> +
> +    if (gnutls_x509_crt_import(cert, &data, GNUTLS_X509_FMT_PEM) < 0) {
> +        virNetError(VIR_ERR_SYSTEM_ERROR,
> +                    _("Unable to import %s certificate %s"),
> +                    isServer ? "server" : "client", certFile);

Shouldn't this and several other instances below rather be something like

        isServer ? _("Unable to import server certificate %s")
                 : _("Unable to import client certificate %s")

to help with translations in case more than just server/client needs changing
in some languages? I have no proof of how probable that is so I don't have a
strong opinion here. If we use the same style all around libvirt, it doesn't
seem necessary not to use it here as well. But if other places have this
right, this should be fixed as well.

> +        goto cleanup;
> +    }
> +
> +    if (gnutls_x509_crt_get_expiration_time(cert) < now) {
> +        virNetError(VIR_ERR_SYSTEM_ERROR,
> +                    _("The %s certificate %s has expired"),
> +                    isServer ? "server" : "client", certFile);
> +        goto cleanup;
> +    }
> +
> +    if (gnutls_x509_crt_get_activation_time(cert) > now) {
> +        virNetError(VIR_ERR_SYSTEM_ERROR,
> +                    _("The %s certificate %s is not yet active"),
> +                    isServer ? "server" : "client", certFile);
> +        goto cleanup;
> +    }
> +
> +    ret = 0;
> +
> +cleanup:
> +    if (ret != 0) {
> +        gnutls_x509_crt_deinit(cert);
> +        cert = NULL;
> +    }
> +    VIR_FREE(buf);
> +    return cert;
> +}
> +
> +
> +static int virNetTLSContextSanityCheckCredentials(bool isServer,
> +                                                  const char *cacertFile,
> +                                                  const char *certFile)
> +{
> +    gnutls_x509_crt_t cert = NULL;
> +    gnutls_x509_crt_t cacert = NULL;
> +    int ret = -1;
> +    unsigned int status;
> +
> +    if (access(certFile, R_OK) == 0) {
> +        if (!(cert = virNetTLSContextSanityCheckCert(isServer, certFile)))
> +            goto cleanup;
> +    }
> +    if (access(cacertFile, R_OK) == 0) {
> +        if (!(cacert = virNetTLSContextSanityCheckCert(isServer, cacertFile)))
> +            goto cleanup;
> +    }
> +    

Looks like a whitespace at EOL.

> +    if (cert && cacert) {
> +        if (gnutls_x509_crt_list_verify(&cert, 1,
> +                                        &cacert, 1,
> +                                        NULL, 0,
> +                                        0, &status) < 0) {
> +            virNetError(VIR_ERR_SYSTEM_ERROR,
> +                        _("Unable to verify %s certificate against CA certificate"),
> +                        isServer ? "server": "client");
> +            goto cleanup;
> +        }
> +
> +        if (status != 0) {
> +            const char *reason = _("Invalid certificate");
> +            

And here.

> +            if (status & GNUTLS_CERT_INVALID)
> +                reason = _("The certificate is not trusted.");
> +            

The same.

> +            if (status & GNUTLS_CERT_SIGNER_NOT_FOUND)
> +                reason = _("The certificate hasn't got a known issuer.");
> +
> +            if (status & GNUTLS_CERT_REVOKED)
> +                reason = _("The certificate has been revoked.");
> +            

And once more.

> +#ifndef GNUTLS_1_0_COMPAT
> +            if (status & GNUTLS_CERT_INSECURE_ALGORITHM)
> +                reason = _("The certificate uses an insecure algorithm");
> +#endif
> +
> +            virNetError(VIR_ERR_SYSTEM_ERROR,
> +                        _("Our own certificate %s failed validation against %s: %s"),
> +                        certFile, cacertFile, reason);
> +            goto cleanup;
> +        }
> +    }
> +
> +    ret = 0;
> +
> +cleanup:
> +    if (cert)
> +        gnutls_x509_crt_deinit(cert);
> +    if (cacert)
> +        gnutls_x509_crt_deinit(cacert);
> +    return ret;
> +}
> +                                           

And here as well.

> +
>  static int virNetTLSContextLoadCredentials(virNetTLSContextPtr ctxt,
>                                             bool isServer,
>                                             const char *cacert,
> @@ -217,6 +343,9 @@ static virNetTLSContextPtr virNetTLSContextNew(const char *cacert,
>          goto error;
>      }
>  
> +    if (virNetTLSContextSanityCheckCredentials(isServer, cacert, cert) < 0)
> +        goto error;
> +
>      if (virNetTLSContextLoadCredentials(ctxt, isServer, cacert, cacrl, cert, key) < 0)
>          goto error;
>  
> @@ -574,15 +703,20 @@ static int virNetTLSContextValidCertificate(virNetTLSContextPtr ctxt,
>          }
>  
>          if (gnutls_x509_crt_get_expiration_time(cert) < now) {
> -            virNetError(VIR_ERR_SYSTEM_ERROR, "%s",
> -                        _("The client certificate has expired"));
> +            /* Warning is reversed from what you expect, since with
> +             * this code it is the Server checking the client and
> +             * vica-verca */

I'd move this comment out of the if statement and s/Warning is/Errors are/ to
make it clearer that it applies to both checks.

> +            virNetError(VIR_ERR_SYSTEM_ERROR,
> +                        _("The %s certificate has expired"),
> +                        sess->isServer ? "client" : "server");
>              gnutls_x509_crt_deinit(cert);
>              goto authdeny;
>          }
>  
>          if (gnutls_x509_crt_get_activation_time(cert) > now) {
> -            virNetError(VIR_ERR_SYSTEM_ERROR, "%s",
> -                        _("The client certificate is not yet active"));
> +            virNetError(VIR_ERR_SYSTEM_ERROR,
> +                        _("The %s certificate is not yet active"),
> +                        sess->isServer ? "client" : "server");
>              gnutls_x509_crt_deinit(cert);
>              goto authdeny;
>          }
> @@ -756,6 +890,8 @@ virNetTLSSessionPtr virNetTLSSessionNew(virNetTLSContextPtr ctxt,
>      gnutls_transport_set_pull_function(sess->session,
>                                         virNetTLSSessionPull);
>  
> +    sess->isServer = ctxt->isServer;
> +
>      return sess;
>  
>  error:

ACK with the nits fixed.

Jirka


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