Regarding 711f8c3fb3db "Bluetooth: L2CAP: Fix accepting connection request for invalid SPSM"

[Cengiz Can <cengiz.can@canonical.com>]

Hello Luiz Augusto,


I'm by no means a bluetooth expert so please bear with me if my
questions sound dumb or pointless.


I'm trying to backport commit 711f8c3fb3db ("Bluetooth: L2CAP: Fix
accepting connection request for invalid SPSM") to v4.15.y and older
stable kernels. (CVE-2022-42896)


According to the changes to `net/bluetooth/l2cap_core.c` there are two
functions that need patching:


* l2cap_le_connect_req
* l2cap_ecred_conn_req



Only the former exists in kernels <= v4.15.y. So I decided to skip

l2cap_ecred_conn_req for older kernels.


Do you think this would be enough to mitigate the issue?



If so, older kernels also lack definitions of L2CAP_CR_LE_BAD_PSM and

L2CAP_PSM_LE_DYN_END.


I see that L2CAP_CR_LE_BAD_PSM is basically the same as
L2CAP_CR_BAD_PSM so I used it to signify an error.


I think it should be enough for the sake of a backport.


What do you think?


Also the range boundary that is defined with L2CAP_PSM_LE_DYN_END is

non-existent in older kernels, and it's hard to decide which value to
use in this expression:

`if (!psm || __le16_to_cpu(psm) > L2CAP_PSM_LE_DYN_END) {`


I can easily define L2CAP_PSM_LE_DYN_END as 0x00FF and call it a day
but I had to ask if we are absolutely sure if that's the right value.


Because the comment block states that it's from the "credit based
connection request" ranges but l2cap_le_connect_req is not credit based.

Is it?

Thank you in advance.

Cengiz Can