From f54d21c38427e68b598546c1c870a289cb5e99bb Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher
Date: Sat, 1 Aug 2020 21:13:00 +0200
Subject: v2api/reverse: implement Lookup & Getattr

---
 internal/fusefrontend_reverse/rpath.go | 102 +++++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)
 create mode 100644 internal/fusefrontend_reverse/rpath.go

(limited to 'internal/fusefrontend_reverse/rpath.go')

diff --git a/internal/fusefrontend_reverse/rpath.go b/internal/fusefrontend_reverse/rpath.go
new file mode 100644
index 0000000..ed37847
--- /dev/null
+++ b/internal/fusefrontend_reverse/rpath.go
@@ -0,0 +1,102 @@
+package fusefrontend_reverse
+
+import (
+	"encoding/base64"
+	"path/filepath"
+	"strings"
+	"syscall"
+
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+	"github.com/rfjakob/gocryptfs/internal/pathiv"
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+// abs basically returns storage dir + "/" + relPath.
+// It takes an error parameter so it can directly wrap decryptPath like this:
+// a, err := rfs.abs(rfs.decryptPath(relPath))
+// abs never generates an error on its own. In other words, abs(p, nil) never
+// fails.
+func (rfs *RootNode) abs(relPath string, err error) (string, error) {
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(rfs.args.Cipherdir, relPath), nil
+}
+
+// rDecryptName decrypts the ciphertext name "cName", given the dirIV of the
+// directory "cName" lies in. The relative plaintext path to the directory
+// "pDir" is used if a "gocryptfs.longname.XYZ.name" must be resolved.
+func (rfs *RootNode) rDecryptName(cName string, dirIV []byte, pDir string) (pName string, err error) {
+	nameType := nametransform.NameType(cName)
+	if nameType == nametransform.LongNameNone {
+		pName, err = rfs.nameTransform.DecryptName(cName, dirIV)
+		if err != nil {
+			// We get lots of decrypt requests for names like ".Trash" that
+			// are invalid base64. Convert them to ENOENT so the correct
+			// error gets returned to the user.
+			if _, ok := err.(base64.CorruptInputError); ok {
+				return "", syscall.ENOENT
+			}
+			// Stat attempts on the link target of encrypted symlinks.
+			// These are always valid base64 but the length is not a
+			// multiple of 16.
+			if err == syscall.EBADMSG {
+				return "", syscall.ENOENT
+			}
+			return "", err
+		}
+	} else if nameType == nametransform.LongNameContent {
+		panic("todo")
+		//pName, err = rfs.findLongnameParent(pDir, dirIV, cName)
+		if err != nil {
+			return "", err
+		}
+	} else {
+		// It makes no sense to decrypt a ".name" file. This is a virtual file
+		// that has no representation in the plaintext filesystem. ".name"
+		// files should have already been handled in virtualfile.go.
+		tlog.Warn.Printf("rDecryptName: cannot decrypt virtual file %q", cName)
+		return "", syscall.EINVAL
+	}
+	return pName, nil
+}
+
+// decryptPath decrypts a relative ciphertext path to a relative plaintext
+// path.
+func (rn *RootNode) decryptPath(relPath string) (string, error) {
+	if rn.args.PlaintextNames || relPath == "" {
+		return relPath, nil
+	}
+	parts := strings.Split(relPath, "/")
+	var transformedParts []string
+	for i := range parts {
+		// Start at the top and recurse
+		currentCipherDir := filepath.Join(parts[:i]...)
+		currentPlainDir := filepath.Join(transformedParts[:i]...)
+		dirIV := pathiv.Derive(currentCipherDir, pathiv.PurposeDirIV)
+		transformedPart, err := rn.rDecryptName(parts[i], dirIV, currentPlainDir)
+		if err != nil {
+			return "", err
+		}
+		transformedParts = append(transformedParts, transformedPart)
+	}
+	pRelPath := filepath.Join(transformedParts...)
+	return pRelPath, nil
+}
+
+// openBackingDir receives an already decrypted relative path
+// "pRelPath", opens the directory that contains the target file/dir
+// and returns the fd to the directory and the decrypted name of the
+// target file. The fd/name pair is intended for use with fchownat and
+// friends.
+func (rn *RootNode) openBackingDir(pRelPath string) (dirfd int, pName string, err error) {
+	// Open directory, safe against symlink races
+	pDir := filepath.Dir(pRelPath)
+	dirfd, err = syscallcompat.OpenDirNofollow(rn.args.Cipherdir, pDir)
+	if err != nil {
+		return -1, "", err
+	}
+	pName = filepath.Base(pRelPath)
+	return dirfd, pName, nil
+}
-- 
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