v2api: implement Lookup()

Compiles, but untested otherwise. No caching.

1 files changed, 68 insertions, 0 deletions

diff --git a/internal/fusefrontend/node_openbackingdir.go b/internal/fusefrontend/node_openbackingdir.go
new file mode 100644
index 0000000..733c239
--- /dev/null
+++ b/internal/fusefrontend/node_openbackingdir.go
@@ -0,0 +1,68 @@
+package fusefrontend
+
+import (
+	"path/filepath"
+	"strings"
+	"syscall"
+
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
+)
+
+// openBackingDir opens the parent ciphertext directory of plaintext path
+// "relPath". It returns the dirfd (opened with O_PATH) and the encrypted
+// basename.
+//
+// The caller should then use Openat(dirfd, cName, ...) and friends.
+// For convenience, if relPath is "", cName is going to be ".".
+//
+// openBackingDir is secure against symlink races by using Openat and
+// ReadDirIVAt.
+func (rn *RootNode) openBackingDir(relPath string) (dirfd int, cName string, err error) {
+	dirRelPath := nametransform.Dir(relPath)
+	// With PlaintextNames, we don't need to read DirIVs. Easy.
+	if rn.args.PlaintextNames {
+		dirfd, err = syscallcompat.OpenDirNofollow(rn.args.Cipherdir, dirRelPath)
+		if err != nil {
+			return -1, "", err
+		}
+		// If relPath is empty, cName is ".".
+		cName = filepath.Base(relPath)
+		return dirfd, cName, nil
+	}
+	// Open cipherdir (following symlinks)
+	dirfd, err = syscall.Open(rn.args.Cipherdir, syscall.O_DIRECTORY|syscallcompat.O_PATH, 0)
+	if err != nil {
+		return -1, "", err
+	}
+	// If relPath is empty, cName is ".".
+	if relPath == "" {
+		return dirfd, ".", nil
+	}
+	// Walk the directory tree
+	parts := strings.Split(relPath, "/")
+	for i, name := range parts {
+		iv, err := nametransform.ReadDirIVAt(dirfd)
+		if err != nil {
+			syscall.Close(dirfd)
+			return -1, "", err
+		}
+		cName, err = rn.nameTransform.EncryptAndHashName(name, iv)
+		if err != nil {
+			syscall.Close(dirfd)
+			return -1, "", err
+		}
+		// Last part? We are done.
+		if i == len(parts)-1 {
+			break
+		}
+		// Not the last part? Descend into next directory.
+		dirfd2, err := syscallcompat.Openat(dirfd, cName, syscall.O_NOFOLLOW|syscall.O_DIRECTORY|syscallcompat.O_PATH, 0)
+		syscall.Close(dirfd)
+		if err != nil {
+			return -1, "", err
+		}
+		dirfd = dirfd2
+	}
+	return dirfd, cName, nil
+}