network plugin: Fix endless loop DOS in parse_packet()

When correct 'Signature part' is received by Collectd, configured without
AuthFile option, condition for endless loop occurs due to missing increase
of pointer to next unprocessed part.

This is a forward-port of #2233.

Fixes: CVE-2017-7401
Closes: #2174
Signed-off-by: Florian Forster <octo@collectd.org>

diff --git a/src/network.c b/src/network.c
index be4c3baeb71b42dbc13ec74e59382c09ced1c488..2ff09af3f9dccea1d9fa4c9d0fe8a077aff1566e 100644 (file)
--- a/src/network.c
+++ b/src/network.c
@@ -1003,14 +1003,6 @@ static int parse_part_sign_sha256(sockent_t *se, /* {{{ */
   buffer_len = *ret_buffer_len;
   buffer_offset = 0;
 
-  if (se->data.server.userdb == NULL) {
-    c_complain(
-        LOG_NOTICE, &complain_no_users,
-        "network plugin: Received signed network packet but can't verify it "
-        "because no user DB has been configured. Will accept it.");
-    return (0);
-  }
-
   /* Check if the buffer has enough data for this structure. */
   if (buffer_len <= PART_SIGNATURE_SHA256_SIZE)
     return (-ENOMEM);
@@ -1027,6 +1019,18 @@ static int parse_part_sign_sha256(sockent_t *se, /* {{{ */
     return (-1);
   }
 
+  if (se->data.server.userdb == NULL) {
+    c_complain(
+        LOG_NOTICE, &complain_no_users,
+        "network plugin: Received signed network packet but can't verify it "
+        "because no user DB has been configured. Will accept it.");
+
+    *ret_buffer = buffer + pss_head_length;
+    *ret_buffer_len -= pss_head_length;
+
+    return (0);
+  }
+
   /* Copy the hash. */
   BUFFER_READ(pss.hash, sizeof(pss.hash));