[PATCH 06/19] smb: server: fix last send credit problem causing disconnects

[Namjae Jeon]

On Thu, Jan 22, 2026 at 4:51 AM Stefan Metzmacher <metze at samba.org> wrote:
>
> When we are about to use the last send credit that was
> granted to us by the peer, we need to wait until
> we are ourself able to grant at least one credit
> to the peer. Otherwise it might not be possible
> for the peer to grant more credits.
>
> The following sections in MS-SMBD are related to this:
>
> 3.1.5.1 Sending Upper Layer Messages
> ...
> If Connection.SendCredits is 1 and the CreditsGranted field of the
> message is 0, stop processing.
> ...
>
> 3.1.5.9 Managing Credits Prior to Sending
> ...
> If Connection.ReceiveCredits is zero, or if Connection.SendCredits is
> one and the Connection.SendQueue is not empty, the sender MUST allocate
> and post at least one receive of size Connection.MaxReceiveSize and MUST
> increment Connection.ReceiveCredits by the number allocated and posted.
> If no receives are posted, the processing MUST return a value of zero to
> indicate to the caller that no Send message can be currently performed.
> ...
>
> This problem was found by running this on Windows 2025
> against ksmbd with required smb signing:
> 'frametest.exe -r 4k -t 20 -n 2000' after
> 'frametest.exe -w 4k -t 20 -n 2000'.
>
> Link: https://lore.kernel.org/linux-cifs/b58fa352-2386-4145-b42e-9b4b1d484e17@samba.org/
> Cc: <stable at vger.kernel.org> # 6.18.x
> Cc: Namjae Jeon <linkinjeon at kernel.org>
> Cc: Steve French <smfrench at gmail.com>
> Cc: Tom Talpey <tom at talpey.com>
> Cc: linux-cifs at vger.kernel.org
> Cc: samba-technical at lists.samba.org
> Signed-off-by: Stefan Metzmacher <metze at samba.org>
Acked-by: Namjae Jeon <linkinjeon at kernel.org>
Thanks!