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

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

[Cengiz Can]

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

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

[Greg KH]

On Tue, Dec 06, 2022 at 02:27:27PM +0300, Cengiz Can wrote:
> 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?

I've already done this backport and it is in the latest -rc1 stable
kernel releases.  Is it not working for you there?  Why do it again?

thanks,

greg k-h

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

[Cengiz Can]

On Tue, 2022-12-06 at 12:49 +0100, Greg KH wrote:
> 
> I've already done this backport and it is in the latest -rc1 stable
> kernel releases.  Is it not working for you there?  Why do it again?

Sorry for the noise. I was just trying to make sure that I'm following
the right path.

I know that 4.4.y is no longer actively maintained but I was trying to
backport it to there as well.

Sorry for the noise again.

Cengiz Can