v2api/reverse: implement Lookup & Getattr

3 files changed, 235 insertions, 0 deletions

diff --git a/internal/fusefrontend_reverse/node.go b/internal/fusefrontend_reverse/node.go
index 6a1294a..a102a66 100644
--- a/internal/fusefrontend_reverse/node.go
+++ b/internal/fusefrontend_reverse/node.go
@@ -1,7 +1,15 @@
 package fusefrontend_reverse
 
 import (
+	"context"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+
 	"github.com/hanwen/go-fuse/v2/fs"
+	"github.com/hanwen/go-fuse/v2/fuse"
+
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
 )
 
 // Node is a file or directory in the filesystem tree
@@ -9,3 +17,61 @@ import (
 type Node struct {
 	fs.Inode
 }
+
+// Lookup - FUSE call for discovering a file.
+// TODO handle virtual files
+func (n *Node) Lookup(ctx context.Context, name string, out *fuse.EntryOut) (ch *fs.Inode, errno syscall.Errno) {
+	dirfd, cName, errno := n.prepareAtSyscall(name)
+	if errno != 0 {
+		return
+	}
+	defer syscall.Close(dirfd)
+
+	// Get device number and inode number into `st`
+	st, err := syscallcompat.Fstatat2(dirfd, cName, unix.AT_SYMLINK_NOFOLLOW)
+	if err != nil {
+		return nil, fs.ToErrno(err)
+	}
+
+	// Create new inode and fill `out`
+	ch = n.newChild(ctx, st, out)
+
+	// Translate ciphertext size in `out.Attr.Size` to plaintext size
+	n.translateSize(dirfd, cName, &out.Attr)
+
+	return ch, 0
+}
+
+// GetAttr - FUSE call for stat()ing a file.
+//
+// GetAttr is symlink-safe through use of openBackingDir() and Fstatat().
+func (n *Node) Getattr(ctx context.Context, f fs.FileHandle, out *fuse.AttrOut) (errno syscall.Errno) {
+	// If the kernel gives us a file handle, use it.
+	if f != nil {
+		return f.(fs.FileGetattrer).Getattr(ctx, out)
+	}
+
+	dirfd, cName, errno := n.prepareAtSyscall("")
+	if errno != 0 {
+		return
+	}
+	defer syscall.Close(dirfd)
+
+	st, err := syscallcompat.Fstatat2(dirfd, cName, unix.AT_SYMLINK_NOFOLLOW)
+	if err != nil {
+		return fs.ToErrno(err)
+	}
+
+	// Fix inode number
+	rn := n.rootNode()
+	rn.inoMap.TranslateStat(st)
+	out.Attr.FromStat(st)
+
+	// Translate ciphertext size in `out.Attr.Size` to plaintext size
+	n.translateSize(dirfd, cName, &out.Attr)
+
+	if rn.args.ForceOwner != nil {
+		out.Owner = *rn.args.ForceOwner
+	}
+	return 0
+}
diff --git a/internal/fusefrontend_reverse/node_helpers.go b/internal/fusefrontend_reverse/node_helpers.go
new file mode 100644
index 0000000..a26ee81
--- /dev/null
+++ b/internal/fusefrontend_reverse/node_helpers.go
@@ -0,0 +1,67 @@
+package fusefrontend_reverse
+
+import (
+	"context"
+	"path/filepath"
+	"syscall"
+
+	"github.com/hanwen/go-fuse/v2/fs"
+	"github.com/hanwen/go-fuse/v2/fuse"
+)
+
+// translateSize translates the ciphertext size in `out` into plaintext size.
+func (n *Node) translateSize(dirfd int, cName string, out *fuse.Attr) {
+	if out.IsRegular() {
+		rn := n.rootNode()
+		out.Size = rn.contentEnc.PlainSizeToCipherSize(out.Size)
+	} else if out.IsSymlink() {
+		panic("todo: call readlink once it is implemented")
+	}
+}
+
+// Path returns the relative plaintext path of this node
+func (n *Node) Path() string {
+	return n.Inode.Path(n.Root())
+}
+
+// rootNode returns the Root Node of the filesystem.
+func (n *Node) rootNode() *RootNode {
+	return n.Root().Operations().(*RootNode)
+}
+
+// prepareAtSyscall returns a (dirfd, cName) pair that can be used
+// with the "___at" family of system calls (openat, fstatat, unlinkat...) to
+// access the backing encrypted directory.
+//
+// If you pass a `child` file name, the (dirfd, cName) pair will refer to
+// a child of this node.
+// If `child` is empty, the (dirfd, cName) pair refers to this node itself.
+func (n *Node) prepareAtSyscall(child string) (dirfd int, cName string, errno syscall.Errno) {
+	p := n.Path()
+	if child != "" {
+		p = filepath.Join(p, child)
+	}
+	rn := n.rootNode()
+	dirfd, cName, err := rn.openBackingDir(p)
+	if err != nil {
+		errno = fs.ToErrno(err)
+	}
+	return
+}
+
+// newChild attaches a new child inode to n.
+// The passed-in `st` will be modified to get a unique inode number.
+func (n *Node) newChild(ctx context.Context, st *syscall.Stat_t, out *fuse.EntryOut) *fs.Inode {
+	// Get unique inode number
+	rn := n.rootNode()
+	rn.inoMap.TranslateStat(st)
+	out.Attr.FromStat(st)
+	// Create child node
+	id := fs.StableAttr{
+		Mode: uint32(st.Mode),
+		Gen:  1,
+		Ino:  st.Ino,
+	}
+	node := &Node{}
+	return n.NewInode(ctx, node, id)
+}
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
+}