[Bug 271991] Crash on some network packets with fresh stable

From: <bugzilla-noreply_at_freebsd.org>
Date: Fri, 16 Jun 2023 19:07:18 UTC

--- Comment #6 from Mark Johnston <markj@FreeBSD.org> ---
So to fix the immediate problem (i.e., the crash):
- ng_bpf should stop copying/pulling up unless "usejit" is set.  bpf_filter()
can handle mbuf chains, it doesn't require a contiguous buffer.  Note that
bpf_mtap() and bpf_mtap2() do not do any pullups or copying.

- Make bpf handle unmapped mbufs.  Note that with unmapped mbufs, protocol
headers will still be mapped, so to trigger any problem you need a BPF program
which reaches into the TCP payload.

Bonus points:
- Teach virtio-net (and probably other paravirtualized NIC drivers, like ena
and gve?) to handle unmapped mbufs.

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