[Bug 1680224] Re: auto.smb fails on Windows administrative shares

[Ian Kent]

The two autofs patches Mark has attached aren't yet available on kernel.org
but I will (eventually) commit them to the autofs repo. and upload them.
The change will be included in autofs-5.1.3.

The only difference between what will be upstream and what has been posted
will be a single line description added to the autofs CHANGELOG (since there
hopefully won't be any further changes needed) and a Signed-off-by line
in the description.

The first patch is not strictly needed but the use of alloca() can be
unreliable in stack overflow conditions as (I believe) it never returns
a failure. So since it was used in the area that needed to be changed
I thought it best to fix it as part of the change.

The patch descriptions hopefully provide enough information for others
to understand what the problem was and why the change fixes the problem.

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https://bugs.launchpad.net/bugs/1680224

Title:
  auto.smb fails on Windows administrative shares

Status in autofs package in Ubuntu:
  Triaged

Bug description:
  This is probably related to #385244.

  I've been unable to get a Windows administrative share (ie. C$)
  mounted through Autofs. Non-administrative shares work fine.
  Administrative shares are accessible with the same credentials from
  other Windows 10 workstations and through smbclient on Ubuntu (16.04
  LTS) machines. Administrative shares can even be mounted using the
  same credentials via mount on the command-line. However, autofs will
  not mount the same shares, using the same credentials, on the same
  Ubuntu machine.

  Administrative shares are listed under /cifs/WindowsHostName, but a cd
  /cifs/WindowsHostname/C$ results in "-bash: cd: C$: No such file or
  directory" from the shell and the following output from 'automount -f
  -v':

  -----
  attempting to mount entry /cifs/WindowsHostname/C$
  >> Retrying with upper case share name
  >> mount error(6): No such device or address
  >> Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
  mount(generic): failed to mount //WindowsHostname/C\$ (type cifs) on /cifs/WindowsHostname/C$
  failed to mount /cifs/WindowsHostname/C$
  -----

  Notice that mount complains of failing to mount 'C\$' rather than
  'C$'. If the bit of awk script that escapes the $ is removed, it then
  fails to mount 'C', which is also no good. I think if we could
  actually get mount to try to mount 'C$', it would work.

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