[PATCH] Cygwin: path: Fix UNC path handling for SMB3 mounted to a drive.

[PATCH] Cygwin: path: Fix UNC path handling for SMB3 mounted to a drive.

[Takashi Yano]

- If an UNC path is mounted to a drive using SMB3.11, accessing to
  the drive fails with error "Too many levels of symbolic links."
  This patch fixes the issue.
---
 winsup/cygwin/path.cc | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/winsup/cygwin/path.cc b/winsup/cygwin/path.cc
index 87ac2404a..4ad4e0821 100644
--- a/winsup/cygwin/path.cc
+++ b/winsup/cygwin/path.cc
@@ -3495,10 +3495,19 @@ restart:
 
 	      /* 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. */
+		 below string comparison has a chance to succeed.
+		 On the contrary, if incoming path has trailing backslash,
+		 but final path does not have one, add trailing backslash
+		 to the final path. */
 	      if (upath.Buffer[(upath.Length - 1) / sizeof (WCHAR)] != L'\\'
-                  && fpbuf[ret - 1] == L'\\')
+		  && fpbuf[ret - 1] == L'\\')
                 fpbuf[--ret] = L'\0';
+	      if (upath.Buffer[(upath.Length - 1) / sizeof (WCHAR)] == L'\\'
+		  && fpbuf[ret - 1] != L'\\' && ret < NT_MAX_PATH - 1)
+		{
+		  fpbuf[ret++] = L'\\';
+		  fpbuf[ret] = L'\0';
+		}
 	      fpbuf[1] = L'?';	/* \\?\ --> \??\ */
 	      RtlInitCountedUnicodeString (&fpath, fpbuf, ret * sizeof (WCHAR));
 	      if (!RtlEqualUnicodeString (&upath, &fpath, !!ci_flag))
-- 
2.34.1

Re: [PATCH] Cygwin: path: Fix UNC path handling for SMB3 mounted to a drive.

[Corinna Vinschen]

On Feb  3 17:40, Takashi Yano wrote:
> - If an UNC path is mounted to a drive using SMB3.11, accessing to
>   the drive fails with error "Too many levels of symbolic links."
>   This patch fixes the issue.

LGTM, please push.

I'm curious.  I'm using Samba as well and never saw this problem.
Can you describe how to reproduce?


Thanks,
Corinna

Re: [PATCH] Cygwin: path: Fix UNC path handling for SMB3 mounted to a drive.

[Takashi Yano]

On Thu, 3 Feb 2022 09:58:19 +0100
Corinna Vinschen wrote:
> On Feb  3 17:40, Takashi Yano wrote:
> > - If an UNC path is mounted to a drive using SMB3.11, accessing to
> >   the drive fails with error "Too many levels of symbolic links."
> >   This patch fixes the issue.
> 
> LGTM, please push.

Thanks for reviewing.

> I'm curious.  I'm using Samba as well and never saw this problem.
> Can you describe how to reproduce?

I used samba under debian stretch last December, and
confirmed current code worked without the problem.

Recently, I have upgraded the server OS from stretch
to bullseye, and noticed this problem.

Perhaps, samba version and its protocol version may be
related.

My samba version is: Version 4.13.13-Debian

This also happens with shared folder under Windows 10
in my environment.

Win10 version is:
Microsoft Windows [Version 10.0.19044.1466]

The reproducible steps are as follows.

$ net use z: '\\server\sharedname'
The command completed successfully.

$ cd /cygdrive/z
/cygdrive/z: Too many levels of symbolic links.
$

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

Re: [PATCH] Cygwin: path: Fix UNC path handling for SMB3 mounted to a drive.

[Takashi Yano]

On Thu, 3 Feb 2022 18:28:32 +0900
Takashi Yano wrote:
> On Thu, 3 Feb 2022 09:58:19 +0100
> Corinna Vinschen wrote:
> > On Feb  3 17:40, Takashi Yano wrote:
> > > - If an UNC path is mounted to a drive using SMB3.11, accessing to
> > >   the drive fails with error "Too many levels of symbolic links."
> > >   This patch fixes the issue.
> > I'm curious.  I'm using Samba as well and never saw this problem.
> > Can you describe how to reproduce?
> 
> I used samba under debian stretch last December, and
> confirmed current code worked without the problem.
> 
> Recently, I have upgraded the server OS from stretch
> to bullseye, and noticed this problem.
> 
> Perhaps, samba version and its protocol version may be
> related.
> 
> My samba version is: Version 4.13.13-Debian

I have just reconfirmed that this problem does not occur
if samba under debian stretch is used even with SMB3.11.

Samba version of stretch is: Version 4.5.16-Debian.

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

Re: [PATCH] Cygwin: path: Fix UNC path handling for SMB3 mounted to a drive.

[Corinna Vinschen]

On Feb  3 19:59, Takashi Yano wrote:
> On Thu, 3 Feb 2022 18:28:32 +0900
> Takashi Yano wrote:
> > On Thu, 3 Feb 2022 09:58:19 +0100
> > Corinna Vinschen wrote:
> > > On Feb  3 17:40, Takashi Yano wrote:
> > > > - If an UNC path is mounted to a drive using SMB3.11, accessing to
> > > >   the drive fails with error "Too many levels of symbolic links."
> > > >   This patch fixes the issue.
> > > I'm curious.  I'm using Samba as well and never saw this problem.
> > > Can you describe how to reproduce?
> > 
> > I used samba under debian stretch last December, and
> > confirmed current code worked without the problem.
> > 
> > Recently, I have upgraded the server OS from stretch
> > to bullseye, and noticed this problem.
> > 
> > Perhaps, samba version and its protocol version may be
> > related.
> > 
> > My samba version is: Version 4.13.13-Debian
> 
> I have just reconfirmed that this problem does not occur
> if samba under debian stretch is used even with SMB3.11.
> 
> Samba version of stretch is: Version 4.5.16-Debian.

Indeed, I can reproduce it.  I'm using Fedora 35 with Samba 4.15.3,
so there's probably a behavioural change.  The reason I didn't
notice it is that I never use drive letters but always UNC paths.

Thanks!


Corinna