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

["Srivatsa S. Bhat" <srivatsa@csail.mit.edu>]

On 2/27/18 4:40 AM, Greg Kroah-Hartman wrote:
> On Tue, Feb 27, 2018 at 01:22:31AM -0800, Srivatsa S. Bhat wrote:
>> On 2/27/18 12:54 AM, Greg Kroah-Hartman wrote:
>>> 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@gmail.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@gmail.com>
>>>>>>>> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.
>>>
>>
>> 4.14 and 4.15 work great! (I had mentioned this is in my original bug
>> report but forgot to summarize it here, sorry).
> 
> 
> Then what is the bugfix that should be applied here in order to keep
> things working with these patches applied?
> 

That would be the one mentioned in the subject line of this thread :)
However, a working backport of that fix is not available for 4.4 and
4.9, hence the trouble.

It looks like we are reconstructing elements of this email thread all
over again, so let me quickly summarize the status so far:

In 4.14/4.15/mainline,
- commit 0603c96f3af50e2f9 (SMB: Validate negotiate (to protect against
  downgrade) even if signing off) caused mount regression with SMB v3.

- commit 4587eee04e2ac7ac3 (SMB3: Validate negotiate request must
  always be signed) fixed the issue.

- [ There was a lot of code churn in the CIFS/SMB codebase between
    these two commits in mainline. ]

In this email thread, you backported the fix to stable 4.13. Thomas
noticed that the problematic commit had also made it to stable series
such as 4.4 and 4.9, and requested a backport of the fix to those
trees as well. However, a straight-forward backport of the fix to 4.4
and 4.9 breaks the build, so no fix was available for those kernels.

I investigated this and tried to produce a working backport of the fix
to 4.4 and 4.9, but didn't succeed, despite trying several variations
as well as suggestions from Aurelien [1][2]. So, given that there is
still no known fix for the mount regression on 4.4 and 4.9 stable
series at this point, I decided to request a revert of the problematic
commit that caused the regression in those kernels.

[1]. https://lkml.org/lkml/2018/1/3/892
[2]. https://lkml.org/lkml/2018/1/29/1009

Regards,
Srivatsa