nbd/server: Refactor zero-length option check

Consolidate the response for a non-zero-length option payload
into a new function, nbd_reject_length().  This check will
also be used when introducing support for structured replies.

Note that STARTTLS response differs based on time: if the connection
is still unencrypted, we set fatal to true (a client that can't
request TLS correctly may still think that we are ready to start
the TLS handshake, so we must disconnect); while if the connection
is already encrypted, the client is sending a bogus request but
is no longer at risk of being confused by continuing the connection.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20171027104037.8319-7-eblake@redhat.com>
[eblake: correct return value on STARTTLS]
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

1 files changed, 46 insertions, 28 deletions

diff --git a/nbd/server.c b/nbd/server.c
index 2f03059..cf81560 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -253,21 +253,10 @@ static int nbd_negotiate_send_rep_list(QIOChannel *ioc, NBDExport *exp,
 
 /* Process the NBD_OPT_LIST command, with a potential series of replies.
  * Return -errno on error, 0 on success. */
-static int nbd_negotiate_handle_list(NBDClient *client, uint32_t length,
-                                     Error **errp)
+static int nbd_negotiate_handle_list(NBDClient *client, Error **errp)
 {
     NBDExport *exp;
 
-    if (length) {
-        if (nbd_drop(client->ioc, length, errp) < 0) {
-            return -EIO;
-        }
-        return nbd_negotiate_send_rep_err(client->ioc,
-                                          NBD_REP_ERR_INVALID, NBD_OPT_LIST,
-                                          errp,
-                                          "OPT_LIST should not have length");
-    }
-
     /* For each export, send a NBD_REP_SERVER reply. */
     QTAILQ_FOREACH(exp, &exports, next) {
         if (nbd_negotiate_send_rep_list(client->ioc, exp, errp)) {
@@ -531,7 +520,6 @@ static int nbd_negotiate_handle_info(NBDClient *client, uint32_t length,
 /* Handle NBD_OPT_STARTTLS. Return NULL to drop connection, or else the
  * new channel for all further (now-encrypted) communication. */
 static QIOChannel *nbd_negotiate_handle_starttls(NBDClient *client,
-                                                 uint32_t length,
                                                  Error **errp)
 {
     QIOChannel *ioc;
@@ -540,15 +528,6 @@ static QIOChannel *nbd_negotiate_handle_starttls(NBDClient *client,
 
     trace_nbd_negotiate_handle_starttls();
     ioc = client->ioc;
-    if (length) {
-        if (nbd_drop(ioc, length, errp) < 0) {
-            return NULL;
-        }
-        nbd_negotiate_send_rep_err(ioc, NBD_REP_ERR_INVALID, NBD_OPT_STARTTLS,
-                                   errp,
-                                   "OPT_STARTTLS should not have length");
-        return NULL;
-    }
 
     if (nbd_negotiate_send_rep(client->ioc, NBD_REP_ACK,
                                NBD_OPT_STARTTLS, errp) < 0) {
@@ -584,6 +563,34 @@ static QIOChannel *nbd_negotiate_handle_starttls(NBDClient *client,
     return QIO_CHANNEL(tioc);
 }
 
+/* nbd_reject_length: Handle any unexpected payload.
+ * @fatal requests that we quit talking to the client, even if we are able
+ * to successfully send an error to the guest.
+ * Return:
+ * -errno  transmission error occurred or @fatal was requested, errp is set
+ * 0       error message successfully sent to client, errp is not set
+ */
+static int nbd_reject_length(NBDClient *client, uint32_t length,
+                             uint32_t option, bool fatal, Error **errp)
+{
+    int ret;
+
+    assert(length);
+    if (nbd_drop(client->ioc, length, errp) < 0) {
+        return -EIO;
+    }
+    ret = nbd_negotiate_send_rep_err(client->ioc, NBD_REP_ERR_INVALID,
+                                     option, errp,
+                                     "option '%s' should have zero length",
+                                     nbd_opt_lookup(option));
+    if (fatal && !ret) {
+        error_setg(errp, "option '%s' should have zero length",
+                   nbd_opt_lookup(option));
+        return -EINVAL;
+    }
+    return ret;
+}
+
 /* nbd_negotiate_options
  * Process all NBD_OPT_* client option commands, during fixed newstyle
  * negotiation.
@@ -674,7 +681,13 @@ static int nbd_negotiate_options(NBDClient *client, uint16_t myflags,
             }
             switch (option) {
             case NBD_OPT_STARTTLS:
-                tioc = nbd_negotiate_handle_starttls(client, length, errp);
+                if (length) {
+                    /* Unconditionally drop the connection if the client
+                     * can't start a TLS negotiation correctly */
+                    return nbd_reject_length(client, length, option, true,
+                                             errp);
+                }
+                tioc = nbd_negotiate_handle_starttls(client, errp);
                 if (!tioc) {
                     return -EIO;
                 }
@@ -710,7 +723,12 @@ static int nbd_negotiate_options(NBDClient *client, uint16_t myflags,
         } else if (fixedNewstyle) {
             switch (option) {
             case NBD_OPT_LIST:
-                ret = nbd_negotiate_handle_list(client, length, errp);
+                if (length) {
+                    ret = nbd_reject_length(client, length, option, false,
+                                            errp);
+                } else {
+                    ret = nbd_negotiate_handle_list(client, errp);
+                }
                 break;
 
             case NBD_OPT_ABORT:
@@ -736,10 +754,10 @@ static int nbd_negotiate_options(NBDClient *client, uint16_t myflags,
                 break;
 
             case NBD_OPT_STARTTLS:
-                if (nbd_drop(client->ioc, length, errp) < 0) {
-                    return -EIO;
-                }
-                if (client->tlscreds) {
+                if (length) {
+                    ret = nbd_reject_length(client, length, option, false,
+                                            errp);
+                } else if (client->tlscreds) {
                     ret = nbd_negotiate_send_rep_err(client->ioc,
                                                      NBD_REP_ERR_INVALID,
                                                      option, errp,