buglwIP - A Lightweight TCP/IP stack - Bugs: bug #57380, Assertion "split <=...


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bug #57380: Assertion "split <= mss" failed

Submitted by:  Hiromasa Ito <vhertz>
Submitted on:  Sat 07 Dec 2019 01:23:36 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 01:23:36 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_out.c:859 fails.

LWIP_ASSERT("split <= mss", split <= pcb->mss);

From my point of view, too small MSS causes this failure.
Incoming packets can set MSS in the range of 0 < MSS < TCP_MSS.
At tcp_in.c:1943, pcb->mss is set as below:

pcb->mss = ((mss > TCP_MSS) || (mss == 0)) ? TCP_MSS : mss;

Therefore, MSS can be set too small.
As a result, it can be smaller than `split` and the assertion fails.

You can reproduce this failure with 'crashed_inputs/009' attached to the following message of lwip-devel:

Hiromasa Ito <vhertz>


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