[Bug 1701073] Re: CVE-2017-2619 regression breaks symlinks

[Dave Kettmann]

I have setup 4 reproducer VMs. All running the base OS and installed
only required packages for Samba. Here are the results:

SMBClient		Xenial	Yakkety	Zesty	Artful
Link to root		Y	Y	Y	Y
Link to directory	Y	Y	Y	Y
Link to file		N	N	N	N

* On Link to file via smbclient, error given is: 
NT_STATUS_ACCESS_DENIED opening remote file \opt\smb.conf

Windows			Xenial	Yakkety	Zesty	Artful
Link to root		Y	N	N	N
Link to directory	N	N	N	N
Link to file		N	N	N	N

* On Link to root on Windows, the “N” gives error “The directory name is
invalid”

Version of Samba on each is:
Xenial	4.3.11+dfsg-0ubuntu0.16.04.7
Yakkety	4.4.5+dfsg-2ubuntu5.6
Zesty	4.5.8+dfsg-0ubuntu0.17.04.2
Artful	4.5.8+dfsg-2ubuntu3

Artful was daily iso downloaded from here on 6/28/2017:
http://cdimage.ubuntu.com/ubuntu-server/daily/current/artful-server-amd64.iso
MD5Sum: ad2f3ef5db99cf91a34903fa61a0c2f2

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https://bugs.launchpad.net/bugs/1701073

Title:
  CVE-2017-2619 regression breaks symlinks

Status in samba:
  Unknown
Status in samba package in Ubuntu:
  New

Bug description:
  Found in current version in Xenial (4.3.11+dfsg-0ubuntu0.16.04.7).
  When share's path is '/', symlinks do not work properly from Windows
  client. Gives "Cannot Access" error.

  To reproduce:

  1. Install samba and related dependencies

  apt install -y samba

  2. Add a share at the end of the default file that uses '/' as the
  path:

  [reproducer]
          comment = share
          browseable = no
          writeable = yes
          create mode = 0600
          directory mode = 0700
          path = /

  3. Attempt to access a symlink somewhere within the path of the share
  with a Windows client.

  4. Receive "Windows cannot access..." related error

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