!83 Reading unbounded number of HTTP/2 CONTINUATION frames to cause excessive CPU usage

Merge pull request !83 from Aurora/zcf_0410_4.0

doc/Makefile.am

@@ -73,6 +73,7 @@ APIDOCS= \
 	nghttp2_option_set_peer_max_concurrent_streams.rst \
 	nghttp2_option_set_server_fallback_rfc7540_priorities.rst \
 	nghttp2_option_set_user_recv_extension_type.rst \
+	nghttp2_option_set_max_continuations.rst \
 	nghttp2_option_set_max_outbound_ack.rst \
 	nghttp2_option_set_max_settings.rst \
 	nghttp2_option_set_stream_reset_rate_limit.rst \

lib/includes/nghttp2/nghttp2.h

@@ -440,7 +440,12 @@ typedef enum {
    * exhaustion on server side to send these frames forever and does
    * not read network.
    */
-  NGHTTP2_ERR_FLOODED = -904
+  NGHTTP2_ERR_FLOODED = -904,
+  /**
+   * When a local endpoint receives too many CONTINUATION frames
+   * following a HEADER frame.
+   */
+  NGHTTP2_ERR_TOO_MANY_CONTINUATIONS = -905,
 } nghttp2_error;
 
 /**
@@ -2743,6 +2748,17 @@ NGHTTP2_EXTERN void
 nghttp2_option_set_stream_reset_rate_limit(nghttp2_option *option,
                                            uint64_t burst, uint64_t rate);
 
+/**
+ * @function
+ *
+ * This function sets the maximum number of CONTINUATION frames
+ * following an incoming HEADER frame.  If more than those frames are
+ * received, the remote endpoint is considered to be misbehaving and
+ * session will be closed.  The default value is 8.
+ */
+NGHTTP2_EXTERN void nghttp2_option_set_max_continuations(nghttp2_option *option,
+                                                         size_t val);
+
 /**
  * @function
  *

lib/nghttp2_helper.c

@@ -336,6 +336,8 @@ const char *nghttp2_strerror(int error_code) {
            "closed";
   case NGHTTP2_ERR_TOO_MANY_SETTINGS:
     return "SETTINGS frame contained more than the maximum allowed entries";
+  case NGHTTP2_ERR_TOO_MANY_CONTINUATIONS:
+    return "Too many CONTINUATION frames following a HEADER frame";
   default:
     return "Unknown error code";
   }

lib/nghttp2_option.c

@@ -150,3 +150,8 @@ void nghttp2_option_set_no_rfc9113_leading_and_trailing_ws_validation(
       NGHTTP2_OPT_NO_RFC9113_LEADING_AND_TRAILING_WS_VALIDATION;
   option->no_rfc9113_leading_and_trailing_ws_validation = val;
 }
+
+void nghttp2_option_set_max_continuations(nghttp2_option *option, size_t val) {
+  option->opt_set_mask |= NGHTTP2_OPT_MAX_CONTINUATIONS;
+  option->max_continuations = val;
+}

lib/nghttp2_option.h

@@ -71,6 +71,7 @@ typedef enum {
   NGHTTP2_OPT_STREAM_RESET_RATE_LIMIT = 1 << 15,
   NGHTTP2_OPT_SERVER_FALLBACK_RFC7540_PRIORITIES = 1 << 13,
   NGHTTP2_OPT_NO_RFC9113_LEADING_AND_TRAILING_WS_VALIDATION = 1 << 14,
+  NGHTTP2_OPT_MAX_CONTINUATIONS = 1 << 16,
 } nghttp2_option_flag;
 
 /**
@@ -98,6 +99,10 @@ struct nghttp2_option {
    * NGHTTP2_OPT_MAX_SETTINGS
    */
   size_t max_settings;
+  /**
+   * NGHTTP2_OPT_MAX_CONTINUATIONS
+   */
+  size_t max_continuations;
   /**
    * Bitwise OR of nghttp2_option_flag to determine that which fields
    * are specified.

lib/nghttp2_session.c

@@ -494,6 +494,7 @@ static int session_new(nghttp2_session **session_ptr,
   (*session_ptr)->max_send_header_block_length = NGHTTP2_MAX_HEADERSLEN;
   (*session_ptr)->max_outbound_ack = NGHTTP2_DEFAULT_MAX_OBQ_FLOOD_ITEM;
   (*session_ptr)->max_settings = NGHTTP2_DEFAULT_MAX_SETTINGS;
+  (*session_ptr)->max_continuations = NGHTTP2_DEFAULT_MAX_CONTINUATIONS;
 
   if (option) {
     if ((option->opt_set_mask & NGHTTP2_OPT_NO_AUTO_WINDOW_UPDATE) &&
@@ -582,6 +583,10 @@ static int session_new(nghttp2_session **session_ptr,
       (*session_ptr)->opt_flags |=
           NGHTTP2_OPTMASK_NO_RFC9113_LEADING_AND_TRAILING_WS_VALIDATION;
     }
+
+    if (option->opt_set_mask & NGHTTP2_OPT_MAX_CONTINUATIONS) {
+      (*session_ptr)->max_continuations = option->max_continuations;
+    }
   }
 
   rv = nghttp2_hd_deflate_init2(&(*session_ptr)->hd_deflater,
@@ -6865,6 +6870,8 @@ ssize_t nghttp2_session_mem_recv(nghttp2_session *session, const uint8_t *in,
           }
         }
         session_inbound_frame_reset(session);
+
+        session->num_continuations = 0;
       }
       break;
     }
@@ -6986,6 +6993,10 @@ ssize_t nghttp2_session_mem_recv(nghttp2_session *session, const uint8_t *in,
       }
 #endif /* DEBUGBUILD */
 
+      if (++session->num_continuations > session->max_continuations) {
+        return NGHTTP2_ERR_TOO_MANY_CONTINUATIONS;
+      }
+
       readlen = inbound_frame_buf_read(iframe, in, last);
       in += readlen;
 

lib/nghttp2_session.h

@@ -110,6 +110,10 @@ typedef struct {
 #define NGHTTP2_DEFAULT_STREAM_RESET_BURST 1000
 #define NGHTTP2_DEFAULT_STREAM_RESET_RATE 33
 
+/* The default max number of CONTINUATION frames following an incoming
+   HEADER frame. */
+#define NGHTTP2_DEFAULT_MAX_CONTINUATIONS 8
+
 /* Internal state when receiving incoming frame */
 typedef enum {
   /* Receiving frame header */
@@ -290,6 +294,12 @@ struct nghttp2_session {
   size_t max_send_header_block_length;
   /* The maximum number of settings accepted per SETTINGS frame. */
   size_t max_settings;
+  /* The maximum number of CONTINUATION frames following an incoming
+     HEADER frame. */
+  size_t max_continuations;
+  /* The number of CONTINUATION frames following an incoming HEADER
+     frame.  This variable is reset when END_HEADERS flag is seen. */
+  size_t num_continuations;
   /* Next Stream ID. Made unsigned int to detect >= (1 << 31). */
   uint32_t next_stream_id;
   /* The last stream ID this session initiated.  For client session,