[PATCH v3 0/7] Add support for DFS in SMB2+

[Aurelien Aptel <aaptel-IBi9RG/b67k@public.gmane.org>]

This series of patch tries to implement the get_dfs_refer operation
for SMB2+.

In SMB2+, DFS resolving is now done through an FSCTL (patch #7). The
relevant Microsoft specifications for this are:

MS-SMB2: 3.2.4.20   Application Requests an IO Control Code Operation
MS-SMB2: 3.2.4.20.3 Application Requests DFS Referral Information
MS-SMB2: 3.2.5.14   Receiving an SMB2 IOCTL Response
MS-SMB2: 3.2.5.14.4 Handling a DFS Referral Information Response

MS-DFSC: 2.2  Message Syntax (but really the whole document is useful)

The DFS response payload however is identical. Patch #1 moves the
DFS response parsing out of SMB1 code and makes it work on any version
of SMB.

DFS code has 2 "main" entry points: initial mounting and automount
(when a DFS link is accessed/traversed).

When automounting, cifs.ko calls build_path_from_dentry() which only
makes treename-prefixed paths when the tcon has the
SMB_IN_DFS_SHARE. This flag is checked in tcon->Flags which is never
touched by SMB2 code as it sets tcon->share_flags on connexion.

* CIFS requires to prefix all pathnames with the treename prefix when
  connected to a DFS server, so the current build_path_from_dentry()
  makes sense for CIFS. 
* For SMB2+ it seems only the Create request requires the treename
  prefix. Simply making the function check for both CIFS SMB2+ flag
  for DFS to add a prefix does not work as the server has different
  expectations about which packet can have/require a DFS pathname.

Patch #2 adds build_path_from_dentry_optional_prefix() with an extra
bool arg to decide to prefix or not. The automount code path always
ask for it. Patch #6 modifies SMB2_open() to add the treename prefix
to the given path if the server requires it.

We try to use an IPC connection first for the DFS request. Patch #3
adds a flag to SMB2_ioctl() to force the usage of ipc_tid. The SMB2
get_dfs_refer operation tries with the flag set and fallback to a
share connection if that doesn't work.

Patch #4 updates the type of ipc_tid from u16 to u32 as that is what a
Tid is in SMB2+. This is correct and really needed since in SMB2 Samba
doesn't use sequential tree id but random ones in the 32bit space.

As part of the mouting process a IPC tcon is made (I suspect we don't
need it anymore in SMB3). This tcon doesn't respect the signing
requirement. This is fixed by patch #5.

Finally the SMB2+ implementation of the get_dfs_referral operation is
added in all supported SMB versions in patch #7.

I've sucessfuly tested this (v1.0 and v3.0) against a Windows Server
2016 DFS setup and a Samba DFS setup.

Samba used to only accepts DFS referrals requests on an IPC connexion,
which is in violation of the spec. A patch was sent on samba-technical
and merged. It is not required anymore.

https://lists.samba.org/archive/samba-technical/2017-February/118859.html

Changes since v2:

* add use_ipc flag to SMB2_open()
* make smb2_get_dfs_refer() try IPC connections first
* use first_entry_or_null() instead of first_entry() on the tcon list
* protect tcon list access with spinlock
* add inc/dec of the tcon reference number, protected by spinlock

Aurelien Aptel (7):
  CIFS: move DFS response parsing out of SMB1 code
  CIFS: add build_path_from_dentry_optional_prefix()
  CIFS: add use_ipc flag to SMB2_ioctl()
  CIFS: let ses->ipc_tid hold smb2 TreeIds
  CIFS: set signing flag in SMB2+ TreeConnect if needed
  CIFS: use DFS pathnames in SMB2+ Create requests
  CIFS: implement get_dfs_refer for SMB2+

 fs/cifs/cifs_dfs_ref.c |   4 +-
 fs/cifs/cifsglob.h     |   2 +-
 fs/cifs/cifspdu.h      |  16 ++++---
 fs/cifs/cifsproto.h    |   7 +++
 fs/cifs/cifssmb.c      | 119 ++---------------------------------------------
 fs/cifs/dir.c          |  13 +++++-
 fs/cifs/misc.c         | 105 +++++++++++++++++++++++++++++++++++++++++
 fs/cifs/smb2file.c     |   3 +-
 fs/cifs/smb2ops.c      | 123 ++++++++++++++++++++++++++++++++++++++++++++++---
 fs/cifs/smb2pdu.c      | 114 +++++++++++++++++++++++++++++++++++++--------
 fs/cifs/smb2pdu.h      |   8 ++++
 fs/cifs/smb2proto.h    |   3 +-
 12 files changed, 365 insertions(+), 152 deletions(-)

-- 
2.10.2