Re: [PATCH v2 1/2] Bluetooth: L2CAP: handle zero txwin_size in ERTM RFC option

[Michael Bommarito]

On Wed, Apr 22, 2026 at 10:44 AM Luiz Augusto von Dentz
<luiz.dentz@xxxxxxxxx> wrote:
> This seems to be going sideways:
>
> https://sashiko.dev/#/patchset/CABBYNZ%2Bf3pur4cSsanQ1kvv-yORp2E0qmVLt9si_%2BFnnJup4Ng%40mail.gmail.com
>
> Patch 2/2 seems totally broken.

Yeah, not a great turn.  I am struggling to figure out where to move
some of these parts and where to put the guards without touching too
much.  As Sashiko pointed out, there are some preexisting bugs or spec
questions that I don't feel like I should be touching unless we expand
this to more of a cleanup + hardening patch set.

If we break this down, there are now ~5 different issues in
adjacent/connected spots:

Ones I was trying to hit or introduced:
1. Zero txwin_size in inbound CONFIG_REQ (ERTM RFC) - original bug.
Need to balance normalization with spec.
2. Repeated CONFIG_RSP re-running l2cap_ertm_init in BT_CONNECTED -
original v2 2/2 target.  We need the guard somewhere safe under the
state model.
3. Zero txwin_size from userspace setsockopt - original v2 1/2 hunk in
l2cap_sock.c.

Pre-existing issues:
3. STREAMING -> ERTM mode switch via late CONF_RSP - pre-existing.
4. l2cap_sock_setsockopt_old locking - pre-existing.

It feels like the safe solution is probably going to be at least +100
or 200 by the time it's done and more than just a hardening patch.  I
can take a spin at it, but I will probably be slower and more
bug-prone than someone else.  No pride of ownership here.  Just let me
know if you want to take the fix over or let me try again

Thanks,
MIke Bommarito