v2api/reverse: implement Lookup for gocryptfs.conf & gocryptfs.diriv

internal/fusefrontend_reverse/node.go

@@ -9,6 +9,8 @@ import (
 	"github.com/hanwen/go-fuse/v2/fs"
 	"github.com/hanwen/go-fuse/v2/fuse"
 
+	"github.com/rfjakob/gocryptfs/internal/configfile"
+	"github.com/rfjakob/gocryptfs/internal/pathiv"
 	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
 )
 
@@ -19,13 +21,56 @@ type Node struct {
 }
 
 // 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, pName, errno := n.prepareAtSyscall(name)
-	if errno != 0 {
+	dirfd := int(-1)
+	pName := ""
+	t := n.lookupFileType(name)
+	// gocryptfs.conf
+	if t == typeConfig {
+		var err error
+		rn := n.rootNode()
+		dirfd, err = syscallcompat.OpenDirNofollow(rn.args.Cipherdir, "")
+		if err != nil {
+			errno = fs.ToErrno(err)
+			return
+		}
+		defer syscall.Close(dirfd)
+		pName = configfile.ConfReverseName
+	} else if t == typeDiriv {
+		// gocryptfs.diriv
+		dirfd, pName, errno = n.prepareAtSyscall("")
+		if errno != 0 {
+			return
+		}
+		defer syscall.Close(dirfd)
+		st, err := syscallcompat.Fstatat2(dirfd, pName, unix.AT_SYMLINK_NOFOLLOW)
+		if err != nil {
+			errno = fs.ToErrno(err)
+			return
+		}
+		content := pathiv.Derive(n.Path(), pathiv.PurposeDirIV)
+		var vf *virtualFile
+		vf, errno = n.newVirtualFile(content, st, inoTagDirIV)
+		if errno != 0 {
+			return nil, errno
+		}
+		out.Attr = vf.attr
+		// Create child node
+		id := fs.StableAttr{Mode: uint32(vf.attr.Mode), Gen: 1, Ino: vf.attr.Ino}
+		ch = n.NewInode(ctx, vf, id)
 		return
+	} else if t == typeName {
+		// gocryptfs.longname.*.name
+
+		// TODO
+	} else if t == typeReal {
+		// real file
+		dirfd, pName, errno = n.prepareAtSyscall(name)
+		if errno != 0 {
+			return
+		}
+		defer syscall.Close(dirfd)
 	}
-	defer syscall.Close(dirfd)
 
 	// Get device number and inode number into `st`
 	st, err := syscallcompat.Fstatat2(dirfd, pName, unix.AT_SYMLINK_NOFOLLOW)
@@ -36,8 +81,10 @@ func (n *Node) Lookup(ctx context.Context, name string, out *fuse.EntryOut) (ch
 	// 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, pName, &out.Attr)
+	if t == typeReal {
+		// Translate ciphertext size in `out.Attr.Size` to plaintext size
+		n.translateSize(dirfd, pName, &out.Attr)
+	}
 
 	return ch, 0
 }

internal/fusefrontend_reverse/virtualfile.go

@@ -1,7 +1,16 @@
 package fusefrontend_reverse
 
 import (
+	"context"
+	"log"
 	"syscall"
+
+	"github.com/hanwen/go-fuse/v2/fs"
+	"github.com/hanwen/go-fuse/v2/fuse"
+
+	"github.com/rfjakob/gocryptfs/internal/configfile"
+	"github.com/rfjakob/gocryptfs/internal/inomap"
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
 )
 
 const (
@@ -13,3 +22,94 @@ const (
 	inoTagDirIV    = 1
 	inoTagNameFile = 2
 )
+
+type fileType int
+
+// Values returned by lookupFileType
+const (
+	// A real file/directory/symlink in the backing plaintext directory
+	typeReal fileType = iota
+	// A DirIV (gocryptfs.diriv) file
+	typeDiriv
+	// A gocryptfs.longname.*.name file for a file with a long name
+	typeName
+	// The config file gocryptfs.conf
+	typeConfig
+)
+
+// lookupFileType returns the type of child file name
+// (one of the fileType constants above). Called from Lookup().
+func (n *Node) lookupFileType(cName string) fileType {
+	rn := n.rootNode()
+	// In -plaintextname mode, neither diriv nor longname files exist.
+	if !rn.args.PlaintextNames {
+		// Is it a gocryptfs.diriv file?
+		if cName == nametransform.DirIVFilename {
+			return typeDiriv
+		}
+		// Is it a gocryptfs.longname.*.name file?
+		if t := nametransform.NameType(cName); t == nametransform.LongNameFilename {
+			return typeName
+		}
+	}
+	// gocryptfs.conf in the root directory. This is passed through to
+	// .gocryptfs.reverse.conf in the backing plaintext directory.
+	if n.isRoot() && !rn.args.ConfigCustom && cName == configfile.ConfDefaultName {
+		return typeConfig
+	}
+	return typeReal
+}
+
+type virtualFile struct {
+	fs.Inode
+
+	// file content
+	content []byte
+	// attributes for Getattr()
+	attr fuse.Attr
+}
+
+// newVirtualFile creates a new in-memory file that does not have a representation
+// on disk. "content" is the file content. Timestamps and file owner are copied
+// from "parentFile" (file descriptor).
+// For a "gocryptfs.diriv" file, you would use the parent directory as
+// "parentFile".
+func (n *Node) newVirtualFile(content []byte, parentStat *syscall.Stat_t, inoTag uint8) (vf *virtualFile, errno syscall.Errno) {
+	if inoTag == 0 {
+		log.Panicf("BUG: inoTag for virtual file is zero - this will cause ino collisions!")
+	}
+
+	// Adjust inode number and size
+	rn := n.rootNode()
+	st := parentStat
+	q := inomap.NewQIno(uint64(st.Dev), inoTag, uint64(st.Ino))
+	st.Ino = rn.inoMap.Translate(q)
+	st.Size = int64(len(content))
+	st.Mode = virtualFileMode
+	st.Nlink = 1
+	var a fuse.Attr
+	a.FromStat(st)
+
+	vf = &virtualFile{content: content, attr: a}
+	return
+}
+
+// Open - FUSE call
+func (f *virtualFile) Open(ctx context.Context, flags uint32) (fh fs.FileHandle, fuseFlags uint32, errno syscall.Errno) {
+	return nil, fuse.FOPEN_KEEP_CACHE, 0
+}
+
+// GetAttr - FUSE call
+func (f *virtualFile) Getattr(ctx context.Context, fh fs.FileHandle, out *fuse.AttrOut) syscall.Errno {
+	out.Attr = f.attr
+	return 0
+}
+
+// Read - FUSE call
+func (f *virtualFile) Read(ctx context.Context, fh fs.FileHandle, dest []byte, off int64) (fuse.ReadResult, syscall.Errno) {
+	end := int(off) + len(dest)
+	if end > len(f.content) {
+		end = len(f.content)
+	}
+	return fuse.ReadResultData(f.content[off:end]), 0
+}