curlsftpsink: authenticate remote host via public key fingerprint

Expose one more libcurl option: CURLOPT_SSH_HOST_PUBLIC_KEY_MD5.
This allows authenticating the server by the MD5 fingerprint of
the server's public key.

https://bugzilla.gnome.org/show_bug.cgi?id=723167

3 files changed, 56 insertions, 2 deletions

diff --git a/ext/curl/gstcurlsshsink.c b/ext/curl/gstcurlsshsink.c
index 91f05f983..7e06dab3d 100644
--- a/ext/curl/gstcurlsshsink.c
+++ b/ext/curl/gstcurlsshsink.c
@@ -48,8 +48,6 @@
 
 /* Default values */
 #define GST_CAT_DEFAULT    gst_curl_ssh_sink_debug
-#define DEFAULT_INSECURE   TRUE
-
 
 /* Plugin specific settings */
 
@@ -63,6 +61,7 @@ enum
   PROP_SSH_PRIV_KEYFILE,
   PROP_SSH_KEY_PASSPHRASE,
   PROP_SSH_KNOWNHOSTS,
+  PROP_SSH_HOST_PUBLIC_KEY_MD5,
   PROP_SSH_ACCEPT_UNKNOWNHOST
 };
 
@@ -159,6 +158,13 @@ gst_curl_ssh_sink_class_init (GstCurlSshSinkClass * klass)
           "The complete path & filename of the SSH 'known_hosts' file",
           NULL, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
 
+  g_object_class_install_property (gobject_class, PROP_SSH_HOST_PUBLIC_KEY_MD5,
+      g_param_spec_string ("ssh-host-pubkey-md5",
+          "MD5 checksum of the remote host's public key",
+          "MD5 checksum (32 hexadecimal digits, case-insensitive) of the "
+          "remote host's public key",
+          NULL, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
   g_object_class_install_property (gobject_class, PROP_SSH_ACCEPT_UNKNOWNHOST,
       g_param_spec_boolean ("ssh-accept-unknownhost",
           "SSH accept unknown host",
@@ -174,6 +180,7 @@ gst_curl_ssh_sink_init (GstCurlSshSink * sink)
   sink->ssh_priv_keyfile = NULL;
   sink->ssh_key_passphrase = NULL;
   sink->ssh_knownhosts = NULL;
+  sink->ssh_host_public_key_md5 = NULL;
   sink->ssh_accept_unknownhost = FALSE;
 }
 
@@ -188,6 +195,7 @@ gst_curl_ssh_sink_finalize (GObject * gobject)
   g_free (this->ssh_priv_keyfile);
   g_free (this->ssh_key_passphrase);
   g_free (this->ssh_knownhosts);
+  g_free (this->ssh_host_public_key_md5);
 
   G_OBJECT_CLASS (parent_class)->finalize (gobject);
 }
@@ -242,6 +250,13 @@ gst_curl_ssh_sink_set_property (GObject * object, guint prop_id,
       GST_DEBUG_OBJECT (sink, "ssh_knownhosts set to %s", sink->ssh_knownhosts);
       break;
 
+    case PROP_SSH_HOST_PUBLIC_KEY_MD5:
+      g_free (sink->ssh_host_public_key_md5);
+      sink->ssh_host_public_key_md5 = g_value_dup_string (value);
+      GST_DEBUG_OBJECT (sink, "ssh_host_public_key_md5 set to %s",
+          sink->ssh_host_public_key_md5);
+      break;
+
     case PROP_SSH_ACCEPT_UNKNOWNHOST:
       sink->ssh_accept_unknownhost = g_value_get_boolean (value);
       GST_DEBUG_OBJECT (sink, "ssh_accept_unknownhost set to %d",
@@ -285,6 +300,10 @@ gst_curl_ssh_sink_get_property (GObject * object, guint prop_id,
       g_value_set_string (value, sink->ssh_knownhosts);
       break;
 
+    case PROP_SSH_HOST_PUBLIC_KEY_MD5:
+      g_value_set_string (value, sink->ssh_host_public_key_md5);
+      break;
+
     case PROP_SSH_ACCEPT_UNKNOWNHOST:
       g_value_set_boolean (value, sink->ssh_accept_unknownhost);
       break;
@@ -329,6 +348,26 @@ gst_curl_ssh_sink_set_options_unlocked (GstCurlBaseSink * bcsink)
     }
   }
 
+  if (sink->ssh_host_public_key_md5) {
+    /* libcurl is freaking tricky. If the input string is not exactly 32
+     * hexdigits long it silently ignores CURLOPT_SSH_HOST_PUBLIC_KEY_MD5 and
+     * performs the transfer without authenticating the server! */
+    if (strlen (sink->ssh_host_public_key_md5) != 32) {
+      GST_ERROR_OBJECT (sink,
+          "MD5-hash string has invalid length, must be exactly 32 hexdigits!");
+      return FALSE;
+    }
+
+    if ((curl_err =
+            curl_easy_setopt (bcsink->curl, CURLOPT_SSH_HOST_PUBLIC_KEY_MD5,
+                sink->ssh_host_public_key_md5)) != CURLE_OK) {
+      GST_ERROR_OBJECT (sink,
+          "curl error: %d setting remote host's public key MD5: %s.", curl_err,
+          sink->ssh_host_public_key_md5);
+      return FALSE;
+    }
+  }
+
   /* make sure we only accept PASSWORD or PUBLICKEY auth methods
    * (can be extended later) */
   if (sink->ssh_auth_type == CURLSSH_AUTH_PASSWORD ||
diff --git a/ext/curl/gstcurlsshsink.h b/ext/curl/gstcurlsshsink.h
index 4e502a3d3..1b56c4d5e 100644
--- a/ext/curl/gstcurlsshsink.h
+++ b/ext/curl/gstcurlsshsink.h
@@ -70,6 +70,8 @@ struct _GstCurlSshSink
                                    CURLOPT_SSH_KNOWN_HOSTS */
   gboolean ssh_accept_unknownhost;      /* accept or reject unknown public key
                                            from remote host */
+  gchar *ssh_host_public_key_md5;   /* MD5-hash of the remote host's public key:
+                                       CURLOPT_SSH_HOST_PUBLIC_KEY_MD5 */
 };
 
 struct _GstCurlSshSinkClass
diff --git a/tests/check/elements/curlsftpsink.c b/tests/check/elements/curlsftpsink.c
index 04774b431..3dd265bd4 100644
--- a/tests/check/elements/curlsftpsink.c
+++ b/tests/check/elements/curlsftpsink.c
@@ -51,6 +51,7 @@ GST_START_TEST (test_properties)
   gchar *res_privkey_file = NULL;
   gchar *res_passphrase = NULL;
   gchar *res_kh_file = NULL;
+  gchar *res_host_pubkey_md5 = NULL;
   guint res_auth_type = 0;
   gboolean res_accept_unkh = FALSE;
 
@@ -73,6 +74,8 @@ GST_START_TEST (test_properties)
   g_object_set (G_OBJECT (sink), "ssh-pub-keyfile", "public_key_file", NULL);
   g_object_set (G_OBJECT (sink), "ssh-priv-keyfile", "private_key_file", NULL);
   g_object_set (G_OBJECT (sink), "ssh-knownhosts", "known_hosts", NULL);
+  g_object_set (G_OBJECT (sink), "ssh-host-pubkey-md5",
+      "00112233445566778899aabbccddeeff", NULL);
   g_object_set (G_OBJECT (sink), "ssh-accept-unknownhost", TRUE, NULL);
   g_object_set (G_OBJECT (sink), "ssh-key-passphrase", "SoMePaSsPhRaSe", NULL);
 
@@ -86,6 +89,7 @@ GST_START_TEST (test_properties)
       "timeout", &res_timeout, "qos-dscp", &res_qos_dscp,
       "ssh-auth-type", &res_auth_type, "ssh-pub-keyfile", &res_pubkey_file,
       "ssh-priv-keyfile", &res_privkey_file, "ssh-knownhosts", &res_kh_file,
+      "ssh-host-pubkey-md5", &res_host_pubkey_md5,
       "ssh-accept-unknownhost", &res_accept_unkh,
       "create-dirs", &res_create_dirs, "ssh-key-passphrase", &res_passphrase,
       NULL);
@@ -107,6 +111,8 @@ GST_START_TEST (test_properties)
           strlen ("private_key_file")) == 0);
   fail_unless (strncmp (res_kh_file, "known_hosts", strlen ("known_hosts"))
       == 0);
+  fail_unless (strncmp (res_host_pubkey_md5, "00112233445566778899aabbccddeeff",
+          strlen ("00112233445566778899aabbccddeeff")) == 0);
   fail_unless (strncmp (res_passphrase, "SoMePaSsPhRaSe",
           strlen ("SoMePaSsPhRaSe")) == 0);
   fail_unless (res_accept_unkh == TRUE);
@@ -120,6 +126,7 @@ GST_START_TEST (test_properties)
   g_free (res_privkey_file);
   g_free (res_passphrase);
   g_free (res_kh_file);
+  g_free (res_host_pubkey_md5);
 
   /* ------- change properties ------------- */
 
@@ -136,6 +143,8 @@ GST_START_TEST (test_properties)
   g_object_set (G_OBJECT (sink), "ssh-pub-keyfile", "/xxx/pub_key", NULL);
   g_object_set (G_OBJECT (sink), "ssh-priv-keyfile", "/yyy/pvt_key", NULL);
   g_object_set (G_OBJECT (sink), "ssh-knownhosts", "/zzz/known_hosts", NULL);
+  g_object_set (G_OBJECT (sink), "ssh-host-pubkey-md5",
+      "ffeeddccbbaa99887766554433221100", NULL);
   g_object_set (G_OBJECT (sink), "ssh-accept-unknownhost", FALSE, NULL);
   g_object_set (G_OBJECT (sink), "ssh-key-passphrase", "OtherPASSphrase", NULL);
 
@@ -150,6 +159,7 @@ GST_START_TEST (test_properties)
       "ssh-auth-type", &res_auth_type, "ssh-pub-keyfile", &res_pubkey_file,
       "ssh-priv-keyfile", &res_privkey_file, "ssh-knownhosts", &res_kh_file,
       "ssh-accept-unknownhost", &res_accept_unkh,
+      "ssh-host-pubkey-md5", &res_host_pubkey_md5,
       "ssh-key-passphrase", &res_passphrase, "create-dirs", &res_create_dirs,
       NULL);
 
@@ -170,6 +180,8 @@ GST_START_TEST (test_properties)
           strlen ("/yyy/pvt_key")) == 0);
   fail_unless (strncmp (res_kh_file, "/zzz/known_hosts",
           strlen ("/zzz/known_host")) == 0);
+  fail_unless (strncmp (res_host_pubkey_md5, "ffeeddccbbaa99887766554433221100",
+          strlen ("ffeeddccbbaa99887766554433221100")) == 0);
   fail_unless (strncmp (res_passphrase, "OtherPASSphrase",
           strlen ("OtherPASSphrase")) == 0);
   fail_unless (res_accept_unkh == FALSE);
@@ -183,6 +195,7 @@ GST_START_TEST (test_properties)
   g_free (res_privkey_file);
   g_free (res_passphrase);
   g_free (res_kh_file);
+  g_free (res_host_pubkey_md5);
 
   cleanup_curlsftpsink (sink);
 }