[Bug 1675698] [NEW] Cannot access anything under a subdirectory if symlinks are disallowed

[David Macek]

Public bug reported:

After upgrading to 4.3.11+dfsg-0ubuntu0.14.04.6, some of my shares broke
in a curious way. The affected shares have `follow symlinks = no`; the
ones with `follow symlinks = yes` aren't affected AFAICT. Allowing
symlinks on one of the affected shares mitigates the issue for that
share.

The issue is that access to anything under a direct subdirectory of the
share doesn't work. I can create a directory in `\\srv\share`, e.g.
`\\srv\share\foo`, but I can't create any files or directories inside
it, e.g. creating `\\srv\share\foo\bar` ends up with error 50 (The
request is not supported). Attempts to access existing files or
directories at this level produce error 59 (An unexpected network error
occured).

The log at level 2 says:

```
../source3/smbd/vfs.c:1298(check_reduced_name)
  check_reduced_name: Bad access attempt: branches is a symlink to foo/bar

```

... or:

```
../source3/smbd/vfs.c:1298(check_reduced_name)
  check_reduced_name: Bad access attempt: . is a symlink to foo
```

** Affects: samba (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1675698

Title:
  Cannot access anything under a subdirectory if symlinks are disallowed

Status in samba package in Ubuntu:
  New

Bug description:
  After upgrading to 4.3.11+dfsg-0ubuntu0.14.04.6, some of my shares
  broke in a curious way. The affected shares have `follow symlinks =
  no`; the ones with `follow symlinks = yes` aren't affected AFAICT.
  Allowing symlinks on one of the affected shares mitigates the issue
  for that share.

  The issue is that access to anything under a direct subdirectory of
  the share doesn't work. I can create a directory in `\\srv\share`,
  e.g. `\\srv\share\foo`, but I can't create any files or directories
  inside it, e.g. creating `\\srv\share\foo\bar` ends up with error 50
  (The request is not supported). Attempts to access existing files or
  directories at this level produce error 59 (An unexpected network
  error occured).

  The log at level 2 says:

  ```
  ../source3/smbd/vfs.c:1298(check_reduced_name)
    check_reduced_name: Bad access attempt: branches is a symlink to foo/bar

  ```

  ... or:

  ```
  ../source3/smbd/vfs.c:1298(check_reduced_name)
    check_reduced_name: Bad access attempt: . is a symlink to foo
  ```

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