[lwip-devel] [bug #57378] Assertion "tcp_slowtimr: persist ticking with empty send buffer" failed

[Hiromasa Ito]

URL:
  <https://savannah.nongnu.org/bugs/?57378>

                 Summary: Assertion "tcp_slowtimr: persist ticking with empty
send buffer" failed
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: vhertz
            Submitted on: Sat 07 Dec 2019 01:19:05 PM UTC
                Category: TCP
                Severity: 3 - Normal
              Item Group: Crash Error
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: Other

    _______________________________________________________

Details:

Hi, all.

This is one of the assertion failures I found by fuzzing (to lwIP
ver2.1.0.RC1).
The following LWIP_ASSERT() at lwip/src/core/tcp.c:1235 fails.


LWIP_ASSERT("tcp_slowtimr: persist ticking with empty send buffer",
pcb->unsent != NULL);


>From my point of view, incoherent pcb->unsent freeing causes this failure.

As far as I know, pcb->unsent is freed at:
- tcp_abansdon()
- tcp_pcb_purge()
- tcp_receive()

In tcp_receive(), pcb->persist_backoff is not cleared after freeing
pcb->unsent.
As a result, pcb->persist_backoff > 0 in spite of pcb->unsent is empty.

You can reproduce this failure with 'crashed_inputs/007' attached to the
following message of lwip-devel:
https://lists.nongnu.org/archive/html/lwip-devel/2019-12/msg00013.html




    _______________________________________________________

Reply to this item at:

  <https://savannah.nongnu.org/bugs/?57378>

_______________________________________________
  Message sent via Savannah
  https://savannah.nongnu.org/