buglwIP - A Lightweight TCP/IP stack - Bugs: bug #57378, Assertion "tcp_slowtimr:...


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bug #57378: Assertion "tcp_slowtimr: persist ticking with empty send buffer" failed

Submitted by:  Hiromasa Ito <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 Planned Release:  None
lwIP version:  Other

Sat 07 Dec 2019 01:19:05 PM UTC, original submission:  

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:

Hiromasa Ito <vhertz>


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