http_static: sanitize path before file read

Romove dot segments from requested target path before start reading
file in file handler to prevent path traversal.

Type: fix

Change-Id: I3bdd3e9d7fffd33c9c8c608169c1dc73423b7078
Signed-off-by: Matus Fabian <matfabia@cisco.com>

src/plugins/http/http.h

@@ -277,6 +277,74 @@ http_state_is_tx_valid (http_conn_t *hc)
 	  state == HTTP_STATE_WAIT_APP_METHOD);
 }
 
+/**
+ * Remove dot segments from path (RFC3986 section 5.2.4)
+ *
+ * @param path Path to sanitize.
+ *
+ * @return New vector with sanitized path.
+ *
+ * The caller is always responsible to free the returned vector.
+ */
+always_inline u8 *
+http_path_remove_dot_segments (u8 *path)
+{
+  u32 *segments = 0, *segments_len = 0, segment_len;
+  u8 *new_path = 0;
+  int i, ii;
+
+  if (!path)
+    return vec_new (u8, 0);
+
+  segments = vec_new (u32, 1);
+  /* first segment */
+  segments[0] = 0;
+  /* find all segments */
+  for (i = 1; i < (vec_len (path) - 1); i++)
+    {
+      if (path[i] == '/')
+	vec_add1 (segments, i + 1);
+    }
+  /* dummy tail */
+  vec_add1 (segments, vec_len (path));
+
+  /* scan all segments for "." and ".." */
+  segments_len = vec_new (u32, vec_len (segments) - 1);
+  for (i = 0; i < vec_len (segments_len); i++)
+    {
+      segment_len = segments[i + 1] - segments[i];
+      if (segment_len == 2 && path[segments[i]] == '.')
+	segment_len = 0;
+      else if (segment_len == 3 && path[segments[i]] == '.' &&
+	       path[segments[i] + 1] == '.')
+	{
+	  segment_len = 0;
+	  /* remove parent (if any) */
+	  for (ii = i - 1; ii >= 0; ii--)
+	    {
+	      if (segments_len[ii])
+		{
+		  segments_len[ii] = 0;
+		  break;
+		}
+	    }
+	}
+      segments_len[i] = segment_len;
+    }
+
+  /* we might end with empty path, so return at least empty vector */
+  new_path = vec_new (u8, 0);
+  /* append all valid segments */
+  for (i = 0; i < vec_len (segments_len); i++)
+    {
+      if (segments_len[i])
+	vec_add (new_path, path + segments[i], segments_len[i]);
+    }
+  vec_free (segments);
+  vec_free (segments_len);
+  return new_path;
+}
+
 #endif /* SRC_PLUGINS_HTTP_HTTP_H_ */
 
 /*

src/plugins/http_static/static_server.c

@@ -357,7 +357,7 @@ try_file_handler (hss_main_t *hsm, hss_session_t *hs, http_req_method_t rt,
 		  u8 *request)
 {
   http_status_code_t sc = HTTP_STATUS_OK;
-  u8 *path;
+  u8 *path, *sanitized_path;
   u32 ce_index;
   http_content_type_t type;
 
@@ -367,6 +367,9 @@ try_file_handler (hss_main_t *hsm, hss_session_t *hs, http_req_method_t rt,
 
   type = content_type_from_request (request);
 
+  /* Remove dot segments to prevent path traversal */
+  sanitized_path = http_path_remove_dot_segments (request);
+
   /*
    * Construct the file to open
    * Browsers are capable of sporadically including a leading '/'
@@ -374,9 +377,9 @@ try_file_handler (hss_main_t *hsm, hss_session_t *hs, http_req_method_t rt,
   if (!request)
     path = format (0, "%s%c", hsm->www_root, 0);
   else if (request[0] == '/')
-    path = format (0, "%s%s%c", hsm->www_root, request, 0);
+    path = format (0, "%s%s%c", hsm->www_root, sanitized_path, 0);
   else
-    path = format (0, "%s/%s%c", hsm->www_root, request, 0);
+    path = format (0, "%s/%s%c", hsm->www_root, sanitized_path, 0);
 
   if (hsm->debug_level > 0)
     clib_warning ("%s '%s'", (rt == HTTP_REQ_GET) ? "GET" : "POST", path);
@@ -419,7 +422,7 @@ try_file_handler (hss_main_t *hsm, hss_session_t *hs, http_req_method_t rt,
   hs->cache_pool_index = ce_index;
 
 done:
-
+  vec_free (sanitized_path);
   hs->content_type = type;
   start_send_data (hs, sc);
   if (!hs->data)