Fix bc break in Windows readlink

GetFinalPathNameByHandleW is given a file handle to a symbolic link,
rather than one to the target, and therefore returns an incorrect path.

Fix symlink with relative path and add test

4 files changed, 125 insertions, 5 deletions

diff --git a/ext/standard/tests/file/windows_links/readlink_compat.phpt b/ext/standard/tests/file/windows_links/readlink_compat.phpt
new file mode 100644
index 0000000000..e119473895
--- /dev/null
+++ b/ext/standard/tests/file/windows_links/readlink_compat.phpt
@@ -0,0 +1,89 @@
+--TEST--
+Test readlink bc behaviour on Windows
+--DESCRIPTION--
+Checks readlink is backward-compatible with PHP-7.3 and below
+--SKIPIF--
+<?php
+if (substr(PHP_OS, 0, 3) != 'WIN') {
+    die('skip windows only test');
+}
+exec('fltmc', $output, $exitCode);
+if ($exitCode !== 0) {
+    die('skip administrator privileges required');
+}
+?>
+--FILE--
+<?php
+$tmpDir = __DIR__ . '\\mnt';
+mkdir($tmpDir);
+
+// mounted volume
+$volume = trim(exec('mountvol C: /L'));
+exec(sprintf('mountvol "%s" %s', $tmpDir, $volume));
+var_dump(readlink($tmpDir)); 
+exec(sprintf('mountvol "%s" /D', $tmpDir));
+
+mkdir($tmpDir . '\\test\\directory', 0777, true);
+chdir($tmpDir . '\\test');
+
+// junction to a volume (same as a mounted volume)
+$link = $tmpDir . '\\test\\volume_junction';
+exec(sprintf('mklink /J "%s" %s', $link, $volume));
+var_dump(readlink($link));
+rmdir($link);
+
+// junction to a directory
+$link = $tmpDir . '\\test\\directory_junction';
+$target = $tmpDir . '\\test\\directory';
+exec(sprintf('mklink /J "%s" "%s"', $link, $target)); 
+var_dump(readlink($link));
+rmdir($link);
+
+// symlink to a directory (absolute and relative)
+$link = $tmpDir . '\\test\\directory_symlink';
+$target = $tmpDir . '\\test\\directory';
+exec(sprintf('mklink /D "%s" "%s"', $link, $target));
+var_dump(readlink($link));
+rmdir($link);
+exec(sprintf('mklink /D "%s" directory', $link));
+var_dump(readlink($link));
+rmdir($link);
+
+// create a file to link to
+$filename = $tmpDir . '\\test\\directory\\a.php';
+$fh = fopen($filename, 'w');
+fclose($fh);
+
+// symlink to a file (absolute and relative)
+$link = $tmpDir . '\\test\\file_symlink';
+exec(sprintf('mklink "%s" "%s"', $link, $filename)); 
+var_dump(readlink($link));
+unlink($link);
+exec(sprintf('mklink "%s" directory\\a.php', $link));
+var_dump(readlink($link));
+unlink($link);
+
+// unexpected behaviour
+echo "\n*** Unexpected behaviour when not a reparse point\n"; 
+var_dump(readlink($tmpDir . '\\test\\directory'));
+var_dump(readlink($filename));
+
+unlink($filename);
+
+chdir(__DIR__);
+rmdir($tmpDir . '\\test\\directory');
+rmdir($tmpDir . '\\test');
+rmdir($tmpDir);
+?>
+--EXPECTF--
+string(3) "C:\"
+string(3) "C:\"
+string(%d) "%s\mnt\test\directory"
+string(%d) "%s\mnt\test\directory"
+string(%d) "%s\mnt\test\directory"
+string(%d) "%s\mnt\test\directory\a.php"
+string(%d) "%s\mnt\test\directory\a.php"
+
+*** Unexpected behaviour when not a reparse point
+string(%d) "%s\mnt\test\directory"
+string(%d) "%s\mnt\test\directory\a.php"
diff --git a/win32/ioutil.c b/win32/ioutil.c
index 7288ea353a..287a9c117c 100644
--- a/win32/ioutil.c
+++ b/win32/ioutil.c
@@ -1004,6 +1004,13 @@ static ssize_t php_win32_ioutil_readlink_int(HANDLE h, wchar_t *buf, size_t buf_
 
 	if (reparse_data->ReparseTag == IO_REPARSE_TAG_SYMLINK) {
 		/* Real symlink */
+
+		/* BC - relative links are shown as absolute */
+		if (reparse_data->SymbolicLinkReparseBuffer.Flags & SYMLINK_FLAG_RELATIVE) {
+			SET_ERRNO_FROM_WIN32_CODE(ERROR_SYMLINK_NOT_SUPPORTED);
+			return -1;
+		}
+
 		reparse_target = reparse_data->SymbolicLinkReparseBuffer.ReparseTarget +
 			(reparse_data->SymbolicLinkReparseBuffer.SubstituteNameOffset /
 			sizeof(wchar_t));
@@ -1095,6 +1102,7 @@ PW32IO ssize_t php_win32_ioutil_readlink_w(const wchar_t *path, wchar_t *buf, si
 	HANDLE h;
 	ssize_t ret;
 
+	/* Get a handle to the symbolic link (if path is a symbolic link) */
 	h = CreateFileW(path,
 					0,
 					0,
@@ -1110,11 +1118,27 @@ PW32IO ssize_t php_win32_ioutil_readlink_w(const wchar_t *path, wchar_t *buf, si
 
 	ret = php_win32_ioutil_readlink_int(h, buf, buf_len);
 
-	if (ret < 0) {
-		/* BC */
-		wchar_t target[PHP_WIN32_IOUTIL_MAXPATHLEN];
-		size_t offset = 0,
-			   target_len = GetFinalPathNameByHandleW(h, target, PHP_WIN32_IOUTIL_MAXPATHLEN, VOLUME_NAME_DOS);
+	if (ret < 0) {		
+		wchar_t target[PHP_WIN32_IOUTIL_MAXPATHLEN];		
+		size_t target_len;
+		size_t offset = 0;
+
+		/* BC - get a handle to the target (if path is a symbolic link) */
+		CloseHandle(h);
+		h = CreateFileW(path,
+						0,
+						0,
+						NULL,
+						OPEN_EXISTING,
+						FILE_FLAG_BACKUP_SEMANTICS,
+						NULL);
+
+		if (h == INVALID_HANDLE_VALUE) {
+			SET_ERRNO_FROM_WIN32_CODE(GetLastError());
+			return -1;
+		}
+
+		target_len = GetFinalPathNameByHandleW(h, target, PHP_WIN32_IOUTIL_MAXPATHLEN, VOLUME_NAME_DOS);
 
 		if(target_len >= buf_len || target_len >= PHP_WIN32_IOUTIL_MAXPATHLEN || target_len == 0) {
 			CloseHandle(h);
diff --git a/win32/ioutil.h b/win32/ioutil.h
index e2906c65e0..34104a3f45 100644
--- a/win32/ioutil.h
+++ b/win32/ioutil.h
@@ -88,6 +88,11 @@ typedef unsigned short mode_t;
 #define F_OK 0x00
 #endif
 
+/* from ntifs.h */
+#ifndef SYMLINK_FLAG_RELATIVE
+#define SYMLINK_FLAG_RELATIVE 0x01
+#endif
+
 typedef struct {
 	DWORD access;
 	DWORD share;
diff --git a/win32/winutil.c b/win32/winutil.c
index cb962fb537..366a48bb11 100644
--- a/win32/winutil.c
+++ b/win32/winutil.c
@@ -398,6 +398,8 @@ PHP_WINUTIL_API int php_win32_code_to_errno(unsigned long w32Err)
         /* 1314 */   ,  {   ERROR_PRIVILEGE_NOT_HELD        ,   EACCES          }
         /* 1816 */  ,   {   ERROR_NOT_ENOUGH_QUOTA          ,   ENOMEM          }
 					,   {   ERROR_ABANDONED_WAIT_0          ,   EIO }
+		/* 1464 */	,	{	ERROR_SYMLINK_NOT_SUPPORTED		,	EINVAL			}
+		/* 4390 */	,	{	ERROR_NOT_A_REPARSE_POINT		,	EINVAL			}
     };
 
     for(i = 0; i < sizeof(errmap)/sizeof(struct code_to_errno_map); ++i)