linux-kernel - Re: [PATCH 4.13 28/43] SMB3: Validate negotiate request must always be signed

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Date:   Tue, 27 Feb 2018 09:54:28 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     "Srivatsa S. Bhat" <srivatsa@...il.mit.edu>
Cc:     Thomas Backlund <tmb@...eia.org>,
        Steve French <smfrench@...il.com>,
        Aurélien Aptel <aaptel@...e.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        lsahlber@...hat.com, pshilov@...rosoft.com,
        linux-cifs@...r.kernel.org
Subject: Re: [PATCH 4.13 28/43] SMB3: Validate negotiate request must always
 be signed

On Mon, Feb 26, 2018 at 07:44:28PM -0800, Srivatsa S. Bhat wrote:
> On 1/3/18 6:15 PM, Srivatsa S. Bhat wrote:
> > On 11/1/17 8:18 AM, Greg Kroah-Hartman wrote:
> >> On Tue, Oct 31, 2017 at 03:02:11PM +0200, Thomas Backlund wrote:
> >>> Den 31.10.2017 kl. 11:55, skrev Greg Kroah-Hartman:
> >>>> 4.13-stable review patch.  If anyone has any objections, please let me know.
> >>>>
> >>>> ------------------
> >>>>
> >>>> From: Steve French <smfrench@...il.com>
> >>>>
> >>>> commit 4587eee04e2ac7ac3ac9fa2bc164fb6e548f99cd upstream.
> >>>>
> >>>> According to MS-SMB2 3.2.55 validate_negotiate request must
> >>>> always be signed. Some Windows can fail the request if you send it unsigned
> >>>>
> >>>> See kernel bugzilla bug 197311
> >>>>
> >>>> Acked-by: Ronnie Sahlberg <lsahlber.redhat.com>
> >>>> Signed-off-by: Steve French <smfrench@...il.com>
> >>>> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> >>>>
> >>>> ---
> >>>>   fs/cifs/smb2pdu.c |    3 +++
> >>>>   1 file changed, 3 insertions(+)
> >>>>
> >>>> --- a/fs/cifs/smb2pdu.c
> >>>> +++ b/fs/cifs/smb2pdu.c
> >>>> @@ -1963,6 +1963,9 @@ SMB2_ioctl(const unsigned int xid, struc
> >>>>   	} else
> >>>>   		iov[0].iov_len = get_rfc1002_length(req) + 4;
> >>>> +	/* validate negotiate request must be signed - see MS-SMB2 3.2.5.5 */
> >>>> +	if (opcode == FSCTL_VALIDATE_NEGOTIATE_INFO)
> >>>> +		req->hdr.sync_hdr.Flags |= SMB2_FLAGS_SIGNED;
> >>>>   	rc = SendReceive2(xid, ses, iov, n_iov, &resp_buftype, flags, &rsp_iov);
> >>>>   	cifs_small_buf_release(req);
> >>>>
> >>>>
> >>>>
> >>>
> >>> This one needs to be backported to all stable kernels as the commit that
> >>> introduced the regression:
> >>> '
> >>> 0603c96f3af50e2f9299fa410c224ab1d465e0f9
> >>> SMB: Validate negotiate (to protect against downgrade) even if signing off
> >>>
> >>> is backported in stable trees as of: 4.9.53, 4.4.90, 3.18.73
> >>
> >> Oh wait, it breaks the builds on older kernels, that's why I didn't
> >> apply it :)
> >>
> >> Can you provide me with a working backport?
> >>
> > 
> > Hi Steve,
> > 
> > Is there a version of this fix available for stable kernels?
> > 
> 
> Hi Greg,
> 
> Mounting SMB3 shares continues to fail for me on 4.4.118 and 4.9.84
> due to the issues that I have described in detail on this mail thread.
> 
> Since there is no apparent fix for this bug on stable kernels, could
> you please consider reverting the original commit that caused this
> regression?
> 
> That commit was intended to enhance security, which is probably why it
> was backported to stable kernels in the first place; but instead it
> ends up breaking basic functionality itself (mounting). So in the
> absence of a proper fix, I don't see much of an option but to revert
> that commit.
> 
> So, please consider reverting the following:
> 
> commit 02ef29f9cbb616bf419 "SMB: Validate negotiate (to protect
> against downgrade) even if signing off" on 4.4.118
> 
> commit 0e1b85a41a25ac888fb "SMB: Validate negotiate (to protect
> against downgrade) even if signing off" on 4.9.84
> 
> They correspond to commit 0603c96f3af50e2f9299fa410c224ab1d465e0f9
> upstream. Both these patches should revert cleanly. 

Do you still have this same problem on 4.14 and 4.15?  If so, the issue
needs to get fixed there, not papered-over by reverting these old
changes, as you will hit the issue again in the future when you update
to a newer kernel version.

thanks,

greg k-h