From 30089b3fbd0d507667e2f74ae91cbab9ec789f44 Mon Sep 17 00:00:00 2001
From: Takashi Yano <takashi.yano@nifty.ne.jp>
Date: Wed, 8 Dec 2021 20:15:45 +0900
Subject: [PATCH] Cygwin: path: Convert UNC path prefix back to drive letter.

- When symlink_info::check() is called with the path having drive
  letter and UNC path is mounted to the drive, the path is replaced
  with UNC path. With this patch, UNC path prefix is converted back
  to drive letter.  This fixes the issue:
  https://cygwin.com/pipermail/cygwin/2021-November/250087.html
  https://cygwin.com/pipermail/cygwin/2021-December/250103.html
---
 winsup/cygwin/path.cc       | 37 ++++++++++++++++++++++++++++++++++++-
 winsup/cygwin/release/3.3.4 |  5 +++++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/path.cc b/winsup/cygwin/path.cc
index baf04ce89..eb1255849 100644
--- a/winsup/cygwin/path.cc
+++ b/winsup/cygwin/path.cc
@@ -3492,10 +3492,45 @@ 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))
+		    {
+		      /* ...get the remote path from the volume path name,
+			 replace remote path with drive letter, check again. */
+		      WCHAR remote[MAX_PATH];
+
+		      fpbuf[1] = L'\\';
+		      BOOL r = GetVolumePathNameW (fpbuf, remote, MAX_PATH);
+		      fpbuf[1] = L'?';
+		      if (r)
+			{
+			  int remlen = wcslen (remote);
+			  if (remote[remlen - 1] == L'\\')
+			    remlen--;
+			  /* Hackfest */
+			  fpath.Buffer[4] = upath.Buffer[4]; /* Drive letter */
+			  fpath.Buffer[5] = L':';
+			  WCHAR *to = fpath.Buffer + 6;
+			  WCHAR *from = to + remlen - 6;
+			  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. */
diff --git a/winsup/cygwin/release/3.3.4 b/winsup/cygwin/release/3.3.4
index f1c32a1a5..4cbfba8eb 100644
--- a/winsup/cygwin/release/3.3.4
+++ b/winsup/cygwin/release/3.3.4
@@ -4,3 +4,8 @@ Bug Fixes
 - Fix a bug in fhandler_dev_clipboard::read() that the second read
   fails with 'Bad address'.
   Addresses: https://cygwin.com/pipermail/cygwin/2021-December/250141.html
+
+- Convert UNC path prefix back to drive letter in symlink_info::check().
+  This solves the following issues:
+  Addresses: https://cygwin.com/pipermail/cygwin/2021-November/250087.html
+             https://cygwin.com/pipermail/cygwin/2021-December/250103.html
-- 
2.43.5