net/http: Do not tear down socket if it's already been torn down

It's possible for data->sock to get torn down in tcp error handling.
If we unconditionally tear it down again we will end up doing writes
to an offset of the NULL pointer when we go to tear it down again.

Detect if it has been torn down and don't do it again.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/net/http.c

@@ -422,7 +422,7 @@ http_establish (struct grub_file *file, grub_off_t offset, int initial)
       return err;
     }
 
-  for (i = 0; !data->headers_recv && i < 100; i++)
+  for (i = 0; data->sock && !data->headers_recv && i < 100; i++)
     {
       grub_net_tcp_retransmit ();
       grub_net_poll_cards (300, &data->headers_recv);
@@ -430,7 +430,8 @@ http_establish (struct grub_file *file, grub_off_t offset, int initial)
 
   if (!data->headers_recv)
     {
-      grub_net_tcp_close (data->sock, GRUB_NET_TCP_ABORT);
+      if (data->sock)
+        grub_net_tcp_close (data->sock, GRUB_NET_TCP_ABORT);
       if (data->err)
 	{
 	  char *str = data->errmsg;