Mail Archives: cygwin/2021/12/08/03:21:08
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| Date: | Wed, 8 Dec 2021 17:20:08 +0900
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| From: | Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
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| To: | cygwin AT cygwin DOT com
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| Subject: | Re: vboxsharedfs - Too many levels of symbolic links
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| Message-Id: | <20211208172008.01b11239c374604abf638a19@nifty.ne.jp>
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| In-Reply-To: | <Ya+WvmECA+zAbuV9@calimero.vinschen.de>
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This is a multi-part message in MIME format.
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On Tue, 7 Dec 2021 18:15:42 +0100
Corinna Vinschen wrote:
> Hi Takashi,
>
> ----- Forwarded message from Corinna Vinschen <corinna-cygwin AT cygwin DOT com> -----
> > The idea of the GFPNBH call is to short-circuit the path_conv handling
> > in case we have native Windows symlinks in the path. My example above
> > was only considering what comes out of the `if ((pc_flags & ...) { ... }
> > ' expression starting in line 3485 (assuming "b" is a native symlink).
> >
> > What I mean is this: Your patch disregards the entire string returned by
> > GFPNBH, if the returned path is an UNC path, no matter what.
> >
> > But what if the incoming path already *was* an UNC path, and potentially
> > contains native symlinks? In that case you have no reason to disregard
> > the resulting path from GFPNBH.
> >
> > And if it was a drive letter path, wouldn't it be nicer to just convert
> > the UNC path prefix back to the drive letter and keep the rest of the
> > final path intact?
> >
> > However, both of these scenarios require extra code, which isn't that
> > important for now, so, never mind.
> ----- End forwarded message -----
>
> What I meant is something like the below (entirely untested). Yeah, I'm
> not sure myself, if it's worth the effort...
>
> diff --git a/winsup/cygwin/autoload.cc b/winsup/cygwin/autoload.cc
> index e254397257fd..06afd2d62996 100644
> --- a/winsup/cygwin/autoload.cc
> +++ b/winsup/cygwin/autoload.cc
> @@ -630,6 +630,7 @@ LoadDLLfunc (LdapMapErrorToWin32, 0, wldap32)
>
> LoadDLLfunc (WNetCloseEnum, 4, mpr)
> LoadDLLfunc (WNetEnumResourceW, 16, mpr)
> +LoadDLLfunc (WNetGetConnectionW, 12, mpr)
> LoadDLLfunc (WNetGetProviderNameW, 12, mpr)
> LoadDLLfunc (WNetGetResourceInformationW, 16, mpr)
> LoadDLLfunc (WNetOpenEnumW, 20, mpr)
> diff --git a/winsup/cygwin/path.cc b/winsup/cygwin/path.cc
> index baf04ce89a08..c7b29acf29b3 100644
> --- a/winsup/cygwin/path.cc
> +++ b/winsup/cygwin/path.cc
> @@ -3492,10 +3492,41 @@ 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))
> {
> + /* Check if the final path is an UNC path and the incoming
> + path isn't. If so... */
> + if (RtlEqualUnicodePathPrefix (&fpath, &ro_u_uncp, TRUE)
> + && !RtlEqualUnicodePathPrefix (&upath, &ro_u_uncp, TRUE))
> + {
> + /* ...extract the drive letter, get the remote path,
> + replace remote path with drive letter, check again. */
> + WCHAR drive[3] = { upath.Buffer[4], L':', L'\0' };
> + WCHAR remote[MAX_PATH];
> +
> + if (WNetGetConnectionW (drive, remote, MAX_PATH)
> + == NO_ERROR)
> + {
> + /* Hackfest */
> + fpath.Buffer[4] = drive[0];
> + fpath.Buffer[5] = L':';
> + WCHAR to = fpath.Buffer + 6;
> + WCHAR from = to + wcslen (remote);
> + memmove (to, from,
> + (wcslen (from) + 1) * sizeof (WCHAR));
> + fpath.Length -= (from - to) * sizeof (WCHAR);
> + if (RtlEqualUnicodeString (&upath, &fpath, !!ci_flag))
> + goto file_not_symlink;
> + }
> + }
> issymlink = true;
> /* upath.Buffer is big enough and unused from this point on.
> Reuse it here, avoiding yet another buffer allocation. */
I confirmed that your patch works nicely.
...except when the drive is created by subst using UNC path,
e.g. subst w: \\server\share.
In this case, WNetGetConnectionW() fails with ERROR_NO_NET_OR_BAD_PATH.
So, I modified your patch a bit.
What about attached patch?
--
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
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