netdev - L2CAP: Spec violation

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Date:   Fri, 4 Nov 2022 12:11:08 -0400
From:   Sungwoo Kim <iam@...g-woo.kim>
To:     marcel@...tmann.org
Cc:     johan.hedberg@...il.com, luiz.dentz@...il.com, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: L2CAP: Spec violation

Hello,

Our fuzzer found a BT spec violation, illegal state transition on L2cap.
Specifically, l2cap_chan::state is transitioned from BT_CONFIG to
BT_DISCONN by CONFIG_RSP by following trace:

l2cap_config_rsp l2cap_core.c:4498
l2cap_send_disconn_req l2cap_core.c:4585
l2cap_state_change l2cap_core.c:1618

According to the spec 5.3 vol.3 part A 6.1.4, CONFIG_RSP cannot cause
that transition, i.e., CONFIG -> DISCONN by CONFIG_RSP is illegal.
It'd be great if we could discuss.

Thanks,
Sungwoo.