linux-kernel - Re: [PATCH] CIFS: Prevent error log on spurious oplock break

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Message-ID: <CANT5p=rB2=DvjtpmVy803emWpuzsy-C2+d4wqQ5g_9fJ8+a5Cw@mail.gmail.com>
Date:   Sun, 7 Mar 2021 16:20:18 +0530
From:   Shyam Prasad N <nspmangalore@...il.com>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc:     Pavel Shilovsky <pshilov@...rosoft.com>,
        Steve French <sfrench@...ba.org>, kernel@...s.com,
        CIFS <linux-cifs@...r.kernel.org>,
        samba-technical <samba-technical@...ts.samba.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] CIFS: Prevent error log on spurious oplock break

Hi Vincent,

The reason for rejecting the request maybe a number of things like:
corrupted request, stale request (for some old session), or for a
wrong handle.
I don't think we should treat any of these cases as a success.

Also, from the MS-SMB2 documentation:
https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-smb2/4f35576a-6f3b-40f0-a832-1c30b0afccb3

"The client MUST locate the file in the GlobalFileTable using the
LeaseKey in the Lease Break Notification. If a file is not found, no
further processing is required."

So I don't think we should be changing the logic here.
If SMB v1 had a different behaviour, we should check if that is as per
the protocol documentation. If not, change it.

Regards,
Shyam

On Fri, Mar 5, 2021 at 3:12 PM Vincent Whitchurch
<vincent.whitchurch@...s.com> wrote:
>
> The SMB1 version of ->is_oplock_break() returns true even if the FileId
> is not found, as long as the oplock break notification message structure
> itself appears to be valid.  A true return value makes
> cifs_demultiplex_thread() to not print an error message for such
> packets.
>
> However, the SMB2 version returns false in such cases, leading to an
> error "No task to wake, unknown frame received!" followed by a hexdump
> of the packet header being printed by cifs_demultiplex_thread().
>
> Note that before commit fa9c2362497fbd64788063288d ("CIFS: Fix SMB2
> oplock break processing"), SMB2 also returned true for the case where a
> connection was found but the FileId was not, but it's not clear to me if
> that commit really intended to change the behaviour of the error prints.
>
> Change the behaviour of SMB2 to be the same as SMB1 and avoid the error
> messages for these packets which we ignore as per the spec.
>
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>
> ---
>  fs/cifs/smb2misc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/cifs/smb2misc.c b/fs/cifs/smb2misc.c
> index 60d4bd1eae2b..3ea3bda64083 100644
> --- a/fs/cifs/smb2misc.c
> +++ b/fs/cifs/smb2misc.c
> @@ -679,7 +679,7 @@ smb2_is_valid_lease_break(char *buffer)
>         }
>         spin_unlock(&cifs_tcp_ses_lock);
>         cifs_dbg(FYI, "Can not process lease break - no lease matched\n");
> -       return false;
> +       return true;
>  }
>
>  bool
> @@ -755,7 +755,7 @@ smb2_is_valid_oplock_break(char *buffer, struct TCP_Server_Info *server)
>         }
>         spin_unlock(&cifs_tcp_ses_lock);
>         cifs_dbg(FYI, "Can not process oplock break for non-existent connection\n");
> -       return false;
> +       return true;
>  }
>
>  void
> --
> 2.28.0
>


-- 
Regards,
Shyam