Signature check for LOGOFF response

[Tom Talpey]

On 3/18/2022 11:20 PM, Enzo Matsumiya wrote:
> Hi,
> 
> The LOGOFF command response is not signed (=> signature is 0x0), but we
> check it anyway, displaying "sign fail" errors in ring buffer.

What server is returning this unsigned response? Assuming it's Windows,
that is either a doc bug or (arguably) a server bug, and should be
reported before deciding how to address it here.

Tom.

> As far as I checked, an explicit LOGOUT is only sent when tlink pruning
> happens (i.e. TLINK_IDLE_EXPIRE expires), but we have a case of this
> causing issues on production env.
> 
> I didn't find LOGOFF being a signature check exception in MS-SMB2 rev64.
> Relevant sections:
> 
> 2.2.7 SMB2 LOGOFF Request
> 2.2.8 SMB2 LOGOFF Response
> 3.2.5.4 Receiving an SMB2 LOGOFF Response
> 3.3.5.6 Receiving an SMB2 LOGOFF Request
> 
> If this is implementation defined, maybe something like this could work?
> (100% untested)
> 
> --- a/fs/cifs/smb2transport.c
> +++ b/fs/cifs/smb2transport.c
> @@ -667,6 +667,7 @@ smb2_verify_signature(struct smb_rqst *rqst, struct 
> TCP_Server_Info *server)
>          if ((shdr->Command == SMB2_NEGOTIATE) ||
>              (shdr->Command == SMB2_SESSION_SETUP) ||
>              (shdr->Command == SMB2_OPLOCK_BREAK) ||
> +           (shdr->Command == SMB2_LOGOFF) ||
>              server->ignore_signature ||
>              (!server->session_estab))
>                  return 0;
> 
> Thoughts?
> 
> 
> Enzo
>