5.4-stable review patch. If anyone has any objections, please let me know.
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From: Luiz Augusto von Dentz luiz.von.dentz@intel.com
[ Upstream commit d24e4a7fedae121d33fb32ad785b87046527eedb ]
Configuration request only configure the incoming direction of the peer initiating the request, so using the MTU is the other direction shall not be used, that said the spec allows the peer responding to adjust:
Bluetooth Core 6.1, Vol 3, Part A, Section 4.5
'Each configuration parameter value (if any is present) in an L2CAP_CONFIGURATION_RSP packet reflects an ‘adjustment’ to a configuration parameter value that has been sent (or, in case of default values, implied) in the corresponding L2CAP_CONFIGURATION_REQ packet.'
That said adjusting the MTU in the response shall be limited to ERTM channels only as for older modes the remote stack may not be able to detect the adjustment causing it to silently drop packets.
Link: https://github.com/bluez/bluez/issues/1422 Link: https://gitlab.archlinux.org/archlinux/packaging/packages/linux/-/issues/149 Link: https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/4793 Fixes: 042bb9603c44 ("Bluetooth: L2CAP: Fix L2CAP MTU negotiation") Signed-off-by: Luiz Augusto von Dentz luiz.von.dentz@intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/bluetooth/l2cap_core.c | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-)
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 4939152f6adc4..1272ad73e4011 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -3484,12 +3484,28 @@ static int l2cap_parse_conf_req(struct l2cap_chan *chan, void *data, size_t data /* Configure output options and let the other side know * which ones we don't like. */
- /* If MTU is not provided in configure request, use the most recently - * explicitly or implicitly accepted value for the other direction, - * or the default value. + /* If MTU is not provided in configure request, try adjusting it + * to the current output MTU if it has been set + * + * Bluetooth Core 6.1, Vol 3, Part A, Section 4.5 + * + * Each configuration parameter value (if any is present) in an + * L2CAP_CONFIGURATION_RSP packet reflects an ‘adjustment’ to a + * configuration parameter value that has been sent (or, in case + * of default values, implied) in the corresponding + * L2CAP_CONFIGURATION_REQ packet. */ - if (mtu == 0) - mtu = chan->imtu ? chan->imtu : L2CAP_DEFAULT_MTU; + if (!mtu) { + /* Only adjust for ERTM channels as for older modes the + * remote stack may not be able to detect that the + * adjustment causing it to silently drop packets. + */ + if (chan->mode == L2CAP_MODE_ERTM && + chan->omtu && chan->omtu != L2CAP_DEFAULT_MTU) + mtu = chan->omtu; + else + mtu = L2CAP_DEFAULT_MTU; + }
if (mtu < L2CAP_DEFAULT_MIN_MTU) result = L2CAP_CONF_UNACCEPT;