Upstream: fixed usage of closed sockets with filter finalization.

When filter finalization is triggered when working with an upstream server,
and error_page redirects request processing to some simple handler,
ngx_http_request_finalize() triggers request termination when the response
is sent.  In particular, via the upstream cleanup handler, nginx will close
the upstream connection and the corresponding socket.

Still, this can happen to be with ngx_event_pipe() on stack.  While
the code will set p->downstream_error due to NGX_ERROR returned from the
output filter chain by filter finalization, otherwise the error will be
ignored till control returns to ngx_http_upstream_process_request().
And event pipe might try reading from the (already closed) socket, resulting
in "readv() failed (9: Bad file descriptor) while reading upstream" errors
(or even segfaults with SSL).

Such errors were seen with the following configuration:

    location /t2 {
        proxy_pass http://127.0.0.1:8080/big;

        image_filter_buffer 10m;
        image_filter   resize  150 100;
        error_page     415   = /empty;
    }

    location /empty {
        return 204;
    }

    location /big {
        # big enough static file
    }

Fix is to clear p->upstream in ngx_http_upstream_finalize_request(),
and ensure that p->upstream is checked in ngx_event_pipe_read_upstream()
and when handling events at ngx_event_pipe() exit.

2 files changed, 10 insertions, 2 deletions

diff --git a/src/event/ngx_event_pipe.c b/src/event/ngx_event_pipe.c
index 54412e130..d774903ec 100644
--- a/src/event/ngx_event_pipe.c
+++ b/src/event/ngx_event_pipe.c
@@ -57,7 +57,9 @@ ngx_event_pipe(ngx_event_pipe_t *p, ngx_int_t do_write)
         do_write = 1;
     }
 
-    if (p->upstream->fd != (ngx_socket_t) -1) {
+    if (p->upstream
+        && p->upstream->fd != (ngx_socket_t) -1)
+    {
         rev = p->upstream->read;
 
         flags = (rev->eof || rev->error) ? NGX_CLOSE_EVENT : 0;
@@ -108,7 +110,9 @@ ngx_event_pipe_read_upstream(ngx_event_pipe_t *p)
     ngx_msec_t    delay;
     ngx_chain_t  *chain, *cl, *ln;
 
-    if (p->upstream_eof || p->upstream_error || p->upstream_done) {
+    if (p->upstream_eof || p->upstream_error || p->upstream_done
+        || p->upstream == NULL)
+    {
         return NGX_OK;
     }
 
diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index a67d50432..2ce9f2114 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -4574,6 +4574,10 @@ ngx_http_upstream_finalize_request(ngx_http_request_t *r,
 
     u->peer.connection = NULL;
 
+    if (u->pipe) {
+        u->pipe->upstream = NULL;
+    }
+
     if (u->pipe && u->pipe->temp_file) {
         ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                        "http upstream temp fd: %d",