Hello,
The TLS enable do not force the use of TLS. For example, if you configure
your director with TLS enable = yes and TLS require = no, clients can
communicate with your director with or without TLS. But if you configure
your director with both TLS enable and TLS require = yes, then all your
clients and storage daemons will only be able to communicate with your
director with TLS.
If you do not set TLS Verify Peer or TLS Allowed CN, then you can use any
Certificate File or Directory. The certificate CN will not be checked
against the Certificate File or Directory configured.
If TLS Verify Peer is enabled, then the peer´s hostname is verified against
the subjectAltName (alternative name) and commonName attributes. This way,
a certificate issued for myclient2.example.com cannot be used, for example,
by a host named myclient1.example.com. Even if they are issued by your own
CA (not a trusted root CA), you have the CN of the certificate file checked
against the hostname (director, client or storage daemon host) that is
using it.
If TLS Allowed CN is enabled, then in addition to the peer´s hostname being
verified, just that ones listed in the "TLS Allowed CN" directives are
permited. If TLS Verify Peer is not enabled and a client uses a "false"
certificate (myclient2 using the myclient1 certificate and myclient1 is in
the allowed CN list, for example) from a host in the allowed CN list of
allowed hosts, it will work.
Openssl functions are used for certificate manipulation (including
validation and verification).
So, it will depend of what you want to have in you TLS communication, even
if using your own CA for the PKI infrastructure used in your bacula TLS
environment. You can have your own CA (a virtual machine for this purpose),
that will be your trusted CA for your environment. And let all your daemons
trust in each other by setting properly the TLS Verify Peer and TLS Allowed
CN directives. I think this should work fine for what you want.
Best regards,
Ana
On Mon, Sep 28, 2015 at 3:03 PM, Egoitz Aurrekoetxea <ego...@ramattack.net>
wrote:
> Have been taking a look to all this in the source code…
>
> It seems that TLS Verify Peer basically ends up by doing (look at bold
> please) :
>
> /*
> * Create a new TLS_CONTEXT instance.
> * Returns: Pointer to TLS_CONTEXT instance on success
> * NULL on failure;
> */
> TLS_CONTEXT *new_tls_context(const char *ca_certfile, const char
> *ca_certdir,
> const char *certfile, const char *keyfile,
> CRYPTO_PEM_PASSWD_CB *pem_callback,
> const void *pem_userdata, const char *dhfile,
> bool verify_peer)
> {
> TLS_CONTEXT *ctx;
> BIO *bio;
> DH *dh;
>
> .
> .
> .
> .
> .
> .
> .
> SSL_CTX_set_default_passwd_cb(ctx->openssl, tls_pem_callback_dispatch);
> SSL_CTX_set_default_passwd_cb_userdata(ctx->openssl, (void *) ctx);
>
> /*
> * Set certificate verification paths. This requires that at least one
> * value be non-NULL
> */
> * if (ca_certfile || ca_certdir) {*
> * if (!SSL_CTX_load_verify_locations(ctx->openssl, ca_certfile,
> ca_certdir)) {*
> * openssl_post_errors(M_FATAL, _("Error loading certificate
> verification stores"));*
> * goto err;*
> * }*
> * } else if (verify_peer) {*
> * /* At least one CA is required for peer verification */*
> * Jmsg0(NULL, M_ERROR, 0, _("Either a certificate file or a directory
> must be"*
> * " specified as a verification store\n"));*
> * goto err;*
> * }*
>
> For later but in the same function to :
>
>
> * /* Verify Peer Certificate */ if (verify_peer) { /*
> SSL_VERIFY_FAIL_IF_NO_PEER_CERT has no effect in client mode */
> SSL_CTX_set_verify(ctx->openssl,
> SSL_VERIFY_PEER|SSL_VERIFY_FAIL_IF_NO_PEER_CERT,
> openssl_verify_peer); }*
>
> It needs a ca public key or a directory with ca public keys….
>
> So I assume that setting properly :
>
> TLS Enable = Yes
> TLS Require = Yes
> TLS Certificate =
> TLS Key =
> TLS Verify Peer =
> TLS CA Certificate File =
>
> it’s enough when you have created all certs with an own (not popularly
> accepted as trusted CA).
>
> The TLS Allowed CN directive, I think it’s just when you use a not
> dedicated CA for the backup or you are using
> a trusted CA where lots of certs could be easily signed (like Thawte) for
> restricting which CN can connect for avoiding
> not authorized valid certs to connect.
>
> And by the way, I think perhaps TLS Verify Peer is not properly documented
> because in :
>
> *http://www.bacula.org/5.1.x-manuals/en/main/main/Bacula_TLS_Communications.html
> <http://www.bacula.org/5.1.x-manuals/en/main/main/Bacula_TLS_Communications.html>
> *it
> sais :
>
> *TLS Verify Peer = yes|no* Verify peer certificate. Instructs server to
> request and verify the client's x509 certificate. Any client certificate
> signed by a known-CA will be accepted unless the TLS Allowed CN
> configuration directive is used, in which case the client certificate must
> correspond to the Allowed Common Name specified. This directive is valid
> only for a server and not in a client context.
>
>
> But in the code, you can see :
>
> /* Verify Peer Certificate */
> if (verify_peer) {
> /* SSL_VERIFY_FAIL_IF_NO_PEER_CERT has no effect in client mode */
> SSL_CTX_set_verify(ctx->openssl,
> *SSL_VERIFY_PEER*|
> *SSL_VERIFY_FAIL_IF_NO_PEER_CERT*,
> openssl_verify_peer);
> }
>
>
> both flags and I have seen you call to new_tls_context from filed.c.
>
> Perhaps this should be corrected in the doc? or am I missing something?.
>
> Best regards,
>
>
>
> El 28/9/2015, a las 15:57, Egoitz Aurrekoetxea <ego...@ramattack.net>
> escribió:
>
> Hi mates,
>
> Have been doing some checks with Bacula and TLS.
>
> At present I have a TLS enable directive, require tis to yes and the ca
> certificate public key (of an own CA) copied in the server and the client.
>
> Now I become an attacker and If I create a new client certificate with the
> same CN as the present used one in bacula-fd and configure bacula-fd to use
> this falsified certificate
> of the falsified ca whose public key is used in the ca cert file directive
> of the bacula-fd, you can’t do from the server (director) a status client.
> This seems to be fine, because it seems
> that like we are not using a known ca (like geotrust, thawte or similar)
> and each other part is not using certificate signed by the ca whose public
> key they have in the config each
> part, the fd and the dir refuse to agree, basically to arrange a TLS
> connection.
>
> So now… my question is then… when is required to use TLS Verify peer in
> the director and the fd?. When someone could use a certificate from Thawte
> for example??. Then you can use
> TLS Allowed CN for even in this situation to avoid using this Thawte’s
> certs in some way?. But how? the CN could be same as the “good” certificate
> one.
>
> What’s the real purpose of verify peer an tls allowed cn?.
>
> Now by the way… the main reason I needed TLS to work fine, is just for
> avoiding an arp poissoning attack to make Bacula store or restore injected
> data in a backup. How could this be done
> noticing that anyone could create a Thawte’s for instance certificate for
> the client, and even you have TLS Allowed CN the CN of the client, as the
> cert is valid, this damage could be caused?
> isn’t it?.
>
> Thanks a lot really,
>
>
>
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