Resource Leak in TCP packet handling in grub, trivial patch

[Manfred Härtel]

I wrote a grub module which uses the TCP communication functions 
included in grub for educating myself. :-)

During stress tests I recognized a resource leak. Naturally, I 
suspected my program first, but could not find a reason why this would 
happen.

Then I got the feeling that the problem has something to do with the 
list of unacked outgoing packets in grub, it seems as if some of them do 
not get unallocated from memory. I also recognized that the unacked 
queue for a certain socket never exceeds the size of 2 packets, even if 
it should actually.

While looking through the source code of tcp.c, I think I found the 
problem and made a trivial patch:

--- tcp.c.orig  2019-09-17 16:38:07.357705163 +0200
+++ tcp.c       2019-09-17 19:41:33.079264637 +0200
@@ -218,7 +218,10 @@
       if (!socket->unack_last)
        socket->unack_first = socket->unack_last = unack;
       else
+      {
        socket->unack_last->next = unack;
+       socket->unack_last = unack;
+      }
     }

   err = grub_net_send_ip_packet (socket->inf, &(socket->out_nla),

Without my patch, a new packet is inserted in the link list after 
socket->unack_last, but socket->unack_last does not change, so when 
another unacked packet comes it is prepended to the same packet in the 
list as before, so the packet we inserted before is not in the linked 
list anymore, and so never gets unallocated.

The patch seems to solve my problem and I did not recognize any side 
effects.