[lwip-devel] [bug #57375] Assertion "mss_local is too small" failed

[Hiromasa Ito]

URL:
  <https://savannah.nongnu.org/bugs/?57375>

                 Summary: Assertion "mss_local is too small" failed
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: vhertz
            Submitted on: Sat 07 Dec 2019 01:13:38 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_out.c:486 fails.


LWIP_ASSERT("mss_local is too small", mss_local >= last_unsent->len +
unsent_optlen);


As described in the assertion, too small MSS causes this failure.
Incomming packets can set MSS in the range of 0 < MSS < TCP_MSS.
At tcp_in.c:1943, pcb->mss is set as below without any other validation:


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


You can reproduce this failure with 'crashed_inputs/004' 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/?57375>

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