[SRU][N/J][PATCH 0/1] Fix L2CAP/LE/CPU/BI-02-C bluetooth certification failure

[Yo-Jung (Leo) Lin]

BugLink: https://bugs.launchpad.net/bugs/2072858

[Impact]

Noble failed the L2CAP/LE/CPU/BI-02-C test in the Porfile Tuning Suite (PTS), 
which Jammy previously could pass.

This is due to new behavior introduced in e4b019515f950b4e6e5b74b2e1bb03a90cb33039.
(Bluetooth: Enforce validation on max value of connection interval). The kernel
only accept Connection Parameter Update Requests whose incoming conn_max_interval
are lower than the current conn_max_interval, and adjust the newer
conn_max_interval to that received max value.

However, this behavior means that conn_max_interval can only decrease, but never
increase. This could potentially make the conditions for connection parameters
narrower over time, causing subsequent connections failed on some devices.
See the issue 847 in bluez upstream[1]. The patch 806a5198c05987b748b50f3d0c0cfb3d417381a4
(Bluetooth: L2CAP: Fix rejecting L2CAP_CONN_PARAM_UPDATE_REQ) in the linux-next
fixed this by accepting connection parameter unconditionally. The relavent test
procedure is also on the mailing list[2].

[1] https://github.com/bluez/bluez/issues/847
[2] https://linuxlists.cc/l/15/linux-bluetooth/t/5350289/(patch_v3)_bluetooth:_l2cap:_fix_rejecting_l2cap_conn_param_update_req#post5352326

[Fix]
Backport the from commit 806a5198c05987b748b50f3d0c0cfb3d417381a4
(Bluetooth: L2CAP: Fix rejecting L2CAP_CONN_PARAM_UPDATE_REQ), which
already in the linux-next.

[1] https://patchwork.kernel.org/project/bluetooth/patch/20240521143521.1568672-1-luiz.dentz@gmail.com/

[Test Case]
1. Install the kernel with the backported patch
2. Run the following test case in the PTS:
 L2CAP/LE/CPU/BI-02-C
 GAP/CONN/CPUP/BV-05-C

[Where problems could occur]
This essentially revert the behavior of accepting L2CAP connection parameters
back to its original state before e4b019515f950b4e6e5b74b2e1bb03a90cb33039
(Bluetooth: Enforce validation on max value of connection interval).

Note that implementing restriction to the conenction parameters may take greater
effort than just adding a few checks in the kernel. The user space, notably the
bluetoothd may also need adjustments[1]. So in this case, removing the half-done
boundary checks in kernel may still do greater good if there's no plan to make
those additional changes.

[1] https://github.com/bluez/bluez/issues/717#issuecomment-1885719058

Luiz Augusto von Dentz (1):
  Bluetooth: L2CAP: Fix rejecting L2CAP_CONN_PARAM_UPDATE_REQ

 include/net/bluetooth/hci_core.h | 36 ++++++++++++++++++++++++++++----
 net/bluetooth/l2cap_core.c       |  8 +------
 2 files changed, 33 insertions(+), 11 deletions(-)

-- 
2.34.1