[Bug 287229] IP reassembly issue in FreeBSD 14.1

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=287229

--- Comment #36 from Gleb Smirnoff <glebius@FreeBSD.org> ---
On Sat Jun 21 08:55:37  2025 UTC, lucas.aubard@irisa.fr wrote:
> How can I disable this feature to test if it indeed provokes the observed
> reassembly inconsistencies ?

Option #1: you can recompile kernel with patched sys/netinet/ip_reass.c.
Change the line

        V_ipq_hashseed = arc4random();

to something non-random, e.g.:

        V_ipq_hashseed = 0;

Option #2: at runtime, before running any of your experiments run kernel
debugger in the write mode:

# kgdb -w

Now it depends if your kernel is compiled with VIMAGE or without. If
compiled without VIMAGE, then it is easy:

(kgbd) set ipq_hashseed = 0

If compiled without VIMAGE, then more complicated:

(kgdb) set *(uint32_t *)(vnet0->vnet_data_base +
(uintptr_t)&vnet_entry_ipq_hashseed) = 0

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