Add support for directory symlinks on Windows

Symlinks with the targets ".", ".." or with an ending slash in the
target are treated as directory symlinks on Windows.

3 files changed, 72 insertions, 17 deletions

diff --git a/libarchive/archive_read_disk_windows.c b/libarchive/archive_read_disk_windows.c
index 57774b15..964de749 100644
--- a/libarchive/archive_read_disk_windows.c
+++ b/libarchive/archive_read_disk_windows.c
@@ -299,7 +299,7 @@ static int	close_and_restore_time(HANDLE, struct tree *,
 		    struct restore_time *);
 static int	setup_sparse_from_disk(struct archive_read_disk *,
 		    struct archive_entry *, HANDLE);
-static int	la_linkname_from_handle(HANDLE, wchar_t **);
+static int	la_linkname_from_handle(HANDLE, wchar_t **, int);
 static int	la_linkname_from_pathw(const wchar_t *, wchar_t **);
 static void	entry_symlink_from_pathw(struct archive_entry *,
 		    const wchar_t *path);
@@ -337,7 +337,7 @@ typedef struct _REPARSE_DATA_BUFFER {
  * outbuf is allocated in the function
  */
 static int
-la_linkname_from_handle(HANDLE h, wchar_t **linkname)
+la_linkname_from_handle(HANDLE h, wchar_t **linkname, int isdir)
 {
 	DWORD inbytes;
 	REPARSE_DATA_BUFFER *buf;
@@ -369,7 +369,8 @@ la_linkname_from_handle(HANDLE h, wchar_t **linkname)
 		return (-1);
 	}
 
-	tbuf = malloc(len + sizeof(wchar_t));
+	/* We need an extra character here to append directory slash */
+	tbuf = malloc(len + 2 * sizeof(wchar_t));
 	if (tbuf == NULL) {
 		free(indata);
 		return (-1);
@@ -391,6 +392,17 @@ la_linkname_from_handle(HANDLE h, wchar_t **linkname)
 			*tbuf = L'/';
 		tbuf++;
 	}
+
+	/*
+	 * Directory symlinks need special treatment
+	 */
+	if (isdir && wcscmp(*linkname, L".") != 0 &&
+	    wcscmp(*linkname, L"..") != 0) {
+		if (*(tbuf - 1) != L'/') {
+			*tbuf = L'/';
+			*(tbuf + 1) = L'\0';
+		}
+	}
 	return (0);
 }
 
@@ -398,17 +410,24 @@ static int
 la_linkname_from_pathw(const wchar_t *path, wchar_t **outbuf)
 {
 	HANDLE h;
+	DWORD attrs;
 	DWORD flag = FILE_FLAG_BACKUP_SEMANTICS |
 	    FILE_FLAG_OPEN_REPARSE_POINT;
 	int ret;
 
+	attrs = GetFileAttributesW(path);
+	if (attrs == INVALID_FILE_ATTRIBUTES ||
+	    (!(attrs & FILE_ATTRIBUTE_REPARSE_POINT)))
+		return (-1);
+
 	h = CreateFileW(path, 0, FILE_SHARE_READ, NULL, OPEN_EXISTING, flag,
 	    NULL);
 	if (h == INVALID_HANDLE_VALUE) {
 		la_dosmaperr(GetLastError());
 		return (-1);
 	}
-	ret = la_linkname_from_handle(h, outbuf);
+	ret = la_linkname_from_handle(h, outbuf,
+	    attrs & FILE_ATTRIBUTE_DIRECTORY);
 	CloseHandle(h);
 	return (ret);
 }
diff --git a/libarchive/archive_write_disk_windows.c b/libarchive/archive_write_disk_windows.c
index 27a2c28f..1155c313 100644
--- a/libarchive/archive_write_disk_windows.c
+++ b/libarchive/archive_write_disk_windows.c
@@ -206,6 +206,7 @@ struct archive_write_disk {
 #define	MAXIMUM_DIR_MODE 0775
 
 static int	disk_unlink(const wchar_t *);
+static int	disk_rmdir(const wchar_t *);
 static int	check_symlinks(struct archive_write_disk *);
 static int	create_filesystem_object(struct archive_write_disk *);
 static struct fixup_entry *current_fixup(struct archive_write_disk *,
@@ -594,7 +595,9 @@ la_CreateSymbolicLinkW(const wchar_t *linkname, const wchar_t *target) {
 	static BOOLEAN (WINAPI *f)(LPCWSTR, LPCWSTR, DWORD);
 	static int set;
 	wchar_t *ttarget, *p;
+	DWORD attrs = 0;
 	DWORD flags = 0;
+	DWORD newflags = 0;
 	BOOL ret = 0;
 
 	if (!set) {
@@ -625,22 +628,49 @@ la_CreateSymbolicLinkW(const wchar_t *linkname, const wchar_t *target) {
 	*p = L'\0';
 
 	/*
-	 * Windows won't overwrite existing links
+	 * If the target equals ".", ".." or ends with a backslash, it always
+	 * points to a directory. In this case we can safely set the directory
+	 * flag. All other symlinks are created as file symlinks.
 	 */
-	disk_unlink(linkname);
+	if (wcscmp(ttarget, L".") == 0 || wcscmp(ttarget, L"..") == 0 ||
+		*(p - 1) == L'\\') {
+#if defined(SYMBOLIC_LINK_FLAG_DIRECTORY)
+		flags |= SYMBOLIC_LINK_FLAG_DIRECTORY;
+#else
+		flags |= 0x1;
+#endif
+		/* Now we remove trailing backslashes, if any */
+		p--;
+		while(*p == L'\\') {
+			*p = L'\0';
+			p--;
+		}
+	}
 
 #if defined(SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE)
-	flags |= SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE;
+	newflags = flags | SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE;
 #else
-	flags |= 0x2;
+	newflags = flags | 0x2;
 #endif
-	ret = (*f)(linkname, ttarget, flags);
+
+	/*
+	 * Windows won't overwrite existing links
+	 */
+	attrs = GetFileAttributesW(linkname);
+	if (attrs != INVALID_FILE_ATTRIBUTES) {
+		if (attrs & FILE_ATTRIBUTE_DIRECTORY)
+			disk_rmdir(linkname);
+		else
+			disk_unlink(linkname);
+	}
+
+	ret = (*f)(linkname, ttarget, newflags);
 	/*
 	 * Prior to Windows 10 calling CreateSymbolicLinkW() will fail
 	 * if SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE is set
 	 */
-	if (!ret && flags != 0) {
-		ret = (*f)(linkname, ttarget, 0);
+	if (!ret) {
+		ret = (*f)(linkname, ttarget, flags);
 	}
 	free(ttarget);
 	return (ret);
@@ -1319,7 +1349,7 @@ disk_unlink(const wchar_t *path)
 }
 
 static int
-disk_rmdir(wchar_t *path)
+disk_rmdir(const wchar_t *path)
 {
 	wchar_t *fullname;
 	int r;
@@ -1918,7 +1948,13 @@ check_symlinks(struct archive_write_disk *a)
 				 * so we can overwrite it with the
 				 * item being extracted.
 				 */
-				if (disk_unlink(a->name)) {
+				if (st.dwFileAttributes &
+				    FILE_ATTRIBUTE_DIRECTORY) {
+					r = disk_rmdir(a->name);
+				} else {
+					r = disk_unlink(a->name);
+				}
+				if (r) {
 					archive_set_error(&a->archive, errno,
 					    "Could not remove symlink %ls",
 					    a->name);
diff --git a/libarchive/test/test_read_disk_directory_traversals.c b/libarchive/test/test_read_disk_directory_traversals.c
index 705b3d98..2990b508 100644
--- a/libarchive/test/test_read_disk_directory_traversals.c
+++ b/libarchive/test/test_read_disk_directory_traversals.c
@@ -570,7 +570,7 @@ test_symlink_hybrid(void)
 	assertMakeDir("h", 0755);
 	assertChdir("h");
 	assertMakeDir("d1", 0755);
-	assertMakeSymlink("ld1", "d1");
+	assertMakeSymlink("ld1", "d1/");
 	assertMakeFile("d1/file1", 0644, "d1/file1");
 	assertMakeFile("d1/file2", 0644, "d1/file2");
 	assertMakeSymlink("d1/link1", "file1");
@@ -727,7 +727,7 @@ test_symlink_logical(void)
 	assertMakeDir("l", 0755);
 	assertChdir("l");
 	assertMakeDir("d1", 0755);
-	assertMakeSymlink("ld1", "d1");
+	assertMakeSymlink("ld1", "d1/");
 	assertMakeFile("d1/file1", 0644, "d1/file1");
 	assertMakeFile("d1/file2", 0644, "d1/file2");
 	assertMakeSymlink("d1/link1", "file1");
@@ -961,8 +961,8 @@ test_symlink_logical_loop(void)
 	assertMakeDir("d1/d2/d3", 0755);
 	assertMakeDir("d2", 0755);
 	assertMakeFile("d2/file1", 0644, "d2/file1");
-	assertMakeSymlink("d1/d2/ld1", "../../d1");
-	assertMakeSymlink("d1/d2/ld2", "../../d2");
+	assertMakeSymlink("d1/d2/ld1", "../../d1/");
+	assertMakeSymlink("d1/d2/ld2", "../../d2/");
 	assertChdir("..");
 
 	assert((ae = archive_entry_new()) != NULL);