v2api: fix missing size translation in Lookup

3 files changed, 120 insertions, 22 deletions

diff --git a/internal/fusefrontend/node.go b/internal/fusefrontend/node.go
index 9d49add..7505f92 100644
--- a/internal/fusefrontend/node.go
+++ b/internal/fusefrontend/node.go
@@ -69,7 +69,13 @@ func (n *Node) Lookup(ctx context.Context, name string, out *fuse.EntryOut) (ch
 	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
 }
 
@@ -98,13 +104,9 @@ func (n *Node) Getattr(ctx context.Context, f fs.FileHandle, out *fuse.AttrOut)
 	rn.inoMap.TranslateStat(st)
 	out.Attr.FromStat(st)
 
-	// Fix size
-	if out.IsRegular() {
-		out.Size = rn.contentEnc.CipherSizeToPlainSize(out.Size)
-	} else if out.IsSymlink() {
-		target, _ := n.Readlink(ctx)
-		out.Size = uint64(len(target))
-	}
+	// 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
 	}
@@ -221,21 +223,7 @@ func (n *Node) Readlink(ctx context.Context) (out []byte, errno syscall.Errno) {
 	}
 	defer syscall.Close(dirfd)
 
-	cTarget, err := syscallcompat.Readlinkat(dirfd, cName)
-	if err != nil {
-		return nil, fs.ToErrno(err)
-	}
-	rn := n.rootNode()
-	if rn.args.PlaintextNames {
-		return []byte(cTarget), 0
-	}
-	// Symlinks are encrypted like file contents (GCM) and base64-encoded
-	target, err := rn.decryptSymlinkTarget(cTarget)
-	if err != nil {
-		tlog.Warn.Printf("Readlink %q: decrypting target failed: %v", cName, err)
-		return nil, syscall.EIO
-	}
-	return []byte(target), 0
+	return n.readlink(dirfd, cName)
 }
 
 // Open - FUSE call. Open already-existing file.
diff --git a/internal/fusefrontend/node_helpers.go b/internal/fusefrontend/node_helpers.go
index a7a32af..a31a41d 100644
--- a/internal/fusefrontend/node_helpers.go
+++ b/internal/fusefrontend/node_helpers.go
@@ -2,10 +2,14 @@ package fusefrontend
 
 import (
 	"context"
+	"syscall"
 
 	"github.com/hanwen/go-fuse/v2/fs"
 
 	"github.com/hanwen/go-fuse/v2/fuse"
+
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
 
 // toFuseCtx tries to extract a fuse.Context from a generic context.Context.
@@ -29,3 +33,33 @@ func toNode(op fs.InodeEmbedder) *Node {
 	}
 	return op.(*Node)
 }
+
+// readlink reads and decrypts a symlink. Used by Readlink, Getattr, Lookup.
+func (n *Node) readlink(dirfd int, cName string) (out []byte, errno syscall.Errno) {
+	cTarget, err := syscallcompat.Readlinkat(dirfd, cName)
+	if err != nil {
+		return nil, fs.ToErrno(err)
+	}
+	rn := n.rootNode()
+	if rn.args.PlaintextNames {
+		return []byte(cTarget), 0
+	}
+	// Symlinks are encrypted like file contents (GCM) and base64-encoded
+	target, err := rn.decryptSymlinkTarget(cTarget)
+	if err != nil {
+		tlog.Warn.Printf("Readlink %q: decrypting target failed: %v", cName, err)
+		return nil, syscall.EIO
+	}
+	return []byte(target), 0
+}
+
+// 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.CipherSizeToPlainSize(out.Size)
+	} else if out.IsSymlink() {
+		target, _ := n.readlink(dirfd, cName)
+		out.Size = uint64(len(target))
+	}
+}
diff --git a/tests/defaults/main_test.go b/tests/defaults/main_test.go
index f59ea38..1982c90 100644
--- a/tests/defaults/main_test.go
+++ b/tests/defaults/main_test.go
@@ -293,3 +293,79 @@ func TestSeekData(t *testing.T) {
 	}
 	f.Close()
 }
+
+/*
+TestMd5sumMaintainers tries to repro this interesting
+bug that was seen during gocryptfs v2.0 development:
+
+$ md5sum linux-3.0/MAINTAINERS linux-3.0/MAINTAINERS linux-3.0/MAINTAINERS linux-3.0/MAINTAINERS
+279b6ab0491e7532132e8f32afe6c04d  linux-3.0/MAINTAINERS <-- WRONG!!!!
+99cc9f0dfd86e63231b94edd43a43e02  linux-3.0/MAINTAINERS <-- correct
+99cc9f0dfd86e63231b94edd43a43e02  linux-3.0/MAINTAINERS
+99cc9f0dfd86e63231b94edd43a43e02  linux-3.0/MAINTAINERS
+
+strace shows:
+
+Bad
+---
+fstat(3, {st_mode=S_IFREG|0644, st_size=196745, ...}) = 0
+read(3, "\n\tList of maintainers and how to"..., 32768) = 32768
+read(3, "M:\tSylwester Nawrocki <s.nawrock"..., 32768) = 32768
+read(3, "rs/scsi/eata*\n\nEATA ISA/EISA/PCI"..., 32768) = 32768
+read(3, "F:\tDocumentation/isapnp.txt\nF:\td"..., 32768) = 32768
+read(3, "hunkeey@googlemail.com>\nL:\tlinux"..., 32768) = 32768
+read(3, "ach-spear3xx/\n\nSPEAR6XX MACHINE "..., 32768) = 32768
+read(3, "", 32768)                      = 0
+lseek(3, 0, SEEK_CUR)                   = 196608
+close(3)                                = 0
+fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0x2), ...}) = 0
+write(1, "279b6ab0491e7532132e8f32afe6c04d"..., 56279b6ab0491e7532132e8f32afe6c04d  linux-3.0/MAINTAINERS
+
+Good
+----
+fstat(3, {st_mode=S_IFREG|0644, st_size=195191, ...}) = 0
+read(3, "\n\tList of maintainers and how to"..., 32768) = 32768
+read(3, "M:\tSylwester Nawrocki <s.nawrock"..., 32768) = 32768
+read(3, "rs/scsi/eata*\n\nEATA ISA/EISA/PCI"..., 32768) = 32768
+read(3, "F:\tDocumentation/isapnp.txt\nF:\td"..., 32768) = 32768
+read(3, "hunkeey@googlemail.com>\nL:\tlinux"..., 32768) = 32768
+read(3, "ach-spear3xx/\n\nSPEAR6XX MACHINE "..., 32768) = 31351
+read(3, "", 4096)                       = 0
+lseek(3, 0, SEEK_CUR)                   = 195191
+close(3)                                = 0
+fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0x2), ...}) = 0
+write(1, "99cc9f0dfd86e63231b94edd43a43e02"..., 5699cc9f0dfd86e63231b94edd43a43e02  linux-3.0/MAINTAINERS
+*/
+func TestMd5sumMaintainers(t *testing.T) {
+	fn := filepath.Join(test_helpers.DefaultPlainDir, t.Name())
+	f, err := os.Create(fn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Size of the MAINTAINERS file = 195191
+	const sizeWant = 195191
+	content := make([]byte, sizeWant)
+	_, err = f.Write(content)
+	if err != nil {
+		t.Fatal(err)
+	}
+	f.Close()
+
+	// Remount to clear the linux kernel attr cache
+	// (otherwise we would have to wait 2 seconds for the entry to expire)
+	test_helpers.UnmountPanic(test_helpers.DefaultPlainDir)
+	test_helpers.MountOrExit(test_helpers.DefaultCipherDir, test_helpers.DefaultPlainDir, "-zerokey")
+
+	cmd := exec.Command("md5sum", fn, fn, fn, fn)
+	out2, err := cmd.CombinedOutput()
+	out := string(out2)
+
+	// 195191 zero bytes have this md5sum
+	const md5Want = "b99bf6917f688068acd49126f3b1b005"
+
+	n := strings.Count(out, md5Want)
+	if n != 4 {
+		t.Errorf("found %d instead of %d instances of %q", n, 4, md5Want)
+		t.Logf("full output:\n%s", out)
+	}
+}