HTTP/2: fix flow control with padded DATA frames.

Previously, flow control didn't account for padding in DATA frames,
which meant that its view of the world could drift from peer's view
by up to 256 bytes per received padded DATA frame, which could lead
to a deadlock.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

1 files changed, 12 insertions, 10 deletions

diff --git a/src/http/v2/ngx_http_v2.c b/src/http/v2/ngx_http_v2.c
index f3050f1db..e17af9ac4 100644
--- a/src/http/v2/ngx_http_v2.c
+++ b/src/http/v2/ngx_http_v2.c
@@ -783,9 +783,12 @@ ngx_http_v2_state_head(ngx_http_v2_connection_t *h2c, u_char *pos, u_char *end)
 static u_char *
 ngx_http_v2_state_data(ngx_http_v2_connection_t *h2c, u_char *pos, u_char *end)
 {
+    size_t                 size;
     ngx_http_v2_node_t    *node;
     ngx_http_v2_stream_t  *stream;
 
+    size = h2c->state.length;
+
     if (h2c->state.flags & NGX_HTTP_V2_PADDED_FLAG) {
 
         if (h2c->state.length == 0) {
@@ -802,33 +805,32 @@ ngx_http_v2_state_data(ngx_http_v2_connection_t *h2c, u_char *pos, u_char *end)
         }
 
         h2c->state.padding = *pos++;
-        h2c->state.length--;
 
-        if (h2c->state.padding > h2c->state.length) {
+        if (h2c->state.padding >= size) {
             ngx_log_error(NGX_LOG_INFO, h2c->connection->log, 0,
                           "client sent padded DATA frame "
                           "with incorrect length: %uz, padding: %uz",
-                          h2c->state.length, h2c->state.padding);
+                          size, h2c->state.padding);
 
             return ngx_http_v2_connection_error(h2c, NGX_HTTP_V2_SIZE_ERROR);
         }
 
-        h2c->state.length -= h2c->state.padding;
+        h2c->state.length -= 1 + h2c->state.padding;
     }
 
     ngx_log_debug0(NGX_LOG_DEBUG_HTTP, h2c->connection->log, 0,
                    "http2 DATA frame");
 
-    if (h2c->state.length > h2c->recv_window) {
+    if (size > h2c->recv_window) {
         ngx_log_error(NGX_LOG_INFO, h2c->connection->log, 0,
                       "client violated connection flow control: "
                       "received DATA frame length %uz, available window %uz",
-                      h2c->state.length, h2c->recv_window);
+                      size, h2c->recv_window);
 
         return ngx_http_v2_connection_error(h2c, NGX_HTTP_V2_FLOW_CTRL_ERROR);
     }
 
-    h2c->recv_window -= h2c->state.length;
+    h2c->recv_window -= size;
 
     if (h2c->recv_window < NGX_HTTP_V2_MAX_WINDOW / 4) {
 
@@ -854,11 +856,11 @@ ngx_http_v2_state_data(ngx_http_v2_connection_t *h2c, u_char *pos, u_char *end)
 
     stream = node->stream;
 
-    if (h2c->state.length > stream->recv_window) {
+    if (size > stream->recv_window) {
         ngx_log_error(NGX_LOG_INFO, h2c->connection->log, 0,
                       "client violated flow control for stream %ui: "
                       "received DATA frame length %uz, available window %uz",
-                      node->id, h2c->state.length, stream->recv_window);
+                      node->id, size, stream->recv_window);
 
         if (ngx_http_v2_terminate_stream(h2c, stream,
                                          NGX_HTTP_V2_FLOW_CTRL_ERROR)
@@ -871,7 +873,7 @@ ngx_http_v2_state_data(ngx_http_v2_connection_t *h2c, u_char *pos, u_char *end)
         return ngx_http_v2_state_skip_padded(h2c, pos, end);
     }
 
-    stream->recv_window -= h2c->state.length;
+    stream->recv_window -= size;
 
     if (stream->no_flow_control
         && stream->recv_window < NGX_HTTP_V2_MAX_WINDOW / 4)