Re: vboxsharedfs - Too many levels of symbolic links

[Takashi Yano <takashi.yano@nifty.ne.jp>]

On Mon, 6 Dec 2021 11:16:30 +0100
Corinna Vinschen wrote:
> > For example, RtlEqualUnicodeString() compares \??\UNC\VBoxSrv\tmp and
> > \??\UNC\VBoxSrv\tmp\, then it fails.
> > [...]
> > +	      if (wcsstr (fpbuf, L"\\\\?\\UNC\\") == fpbuf)
> > +		goto file_not_symlink;
> > +
> 
> Isn't that a bit intrusive?  Wouldn't it also fix the issue if we
> just overwrite a trailing '\\' with '\0', like this?
> 
> diff --git a/winsup/cygwin/path.cc b/winsup/cygwin/path.cc
> index baf04ce89a08..b76e5b0466cf 100644
> --- a/winsup/cygwin/path.cc
> +++ b/winsup/cygwin/path.cc
> @@ -3492,8 +3492,14 @@ restart:
>  	    {
>  	      UNICODE_STRING fpath;
>  
> -	      RtlInitCountedUnicodeString (&fpath, fpbuf, ret * sizeof (WCHAR));
> +	      /* If incoming path has no trailing backslash, but final path
> +	         has one, drop trailing backslash from final path so the
> +		 below string comparison has a chance to succeed. */
> +	      if (upath.Buffer[(upath.Length - 1) / sizeof (WCHAR)] != L'\\'
> +		  && fpbuf[ret - 1] == L'\\')
> +		fpbuf[--ret] = L'\0';
>  	      fpbuf[1] = L'?';	/* \\?\ --> \??\ */
> +	      RtlInitCountedUnicodeString (&fpath, fpbuf, ret * sizeof (WCHAR));
>  	      if (!RtlEqualUnicodeString (&upath, &fpath, !!ci_flag))
>  	        {
>  		  issymlink = true;

First, I think the same. However, with this patch, it sometimes causes
hang for a few seconds around the code:
	      else if (isvirtual_dev (dev))
		{
		  /* FIXME: Calling build_fhandler here is not the right way to
			    handle this. */
		  fhandler_virtual *fh = (fhandler_virtual *)
					 build_fh_dev (dev, path_copy);
		  virtual_ftype_t file_type;
		  if (!fh)
		    file_type = virt_none;
		  else
		    {
		      file_type = fh->exists ();
		      if (file_type == virt_symlink
			  || file_type == virt_fdsymlink)
			{
			  fh->fill_filebuf ();
			  symlen = sym.set (fh->get_filebuf ());
			}

with path_copy of "//VBoxSrv". I am not sure why.

In addition,
https://cygwin.com/pipermail/cygwin/2021-December/250103.html
still needs fix.

So I proposed the patch which stops to treat UNC path as symlink.

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>