3 files changed, 34 insertions, 14 deletions
diff --git a/internal/fusefrontend/fs.go b/internal/fusefrontend/fs.go
index 2c6ac5a..9637acf 100644
--- a/internal/fusefrontend/fs.go
+++ b/internal/fusefrontend/fs.go
@@ -319,6 +319,10 @@ func (fs *FS) Mknod(path string, mode uint32, dev uint32, context *fuse.Context)
 		return fuse.ToStatus(err)
 	}
 	defer syscall.Close(dirfd)
+	// Make sure context is nil if we don't want to preserve the owner
+	if !fs.args.PreserveOwner {
+		context = nil
+	}
 	// Create ".name" file to store long file name (except in PlaintextNames mode)
 	if !fs.args.PlaintextNames && nametransform.IsLongContent(cName) {
 		err = fs.nameTransform.WriteLongNameAt(dirfd, cName, path)
@@ -326,26 +330,15 @@ func (fs *FS) Mknod(path string, mode uint32, dev uint32, context *fuse.Context)
 			return fuse.ToStatus(err)
 		}
 		// Create "gocryptfs.longfile." device node
-		err = syscallcompat.Mknodat(dirfd, cName, mode, int(dev))
+		err = syscallcompat.MknodatUser(dirfd, cName, mode, int(dev), context)
 		if err != nil {
 			nametransform.DeleteLongNameAt(dirfd, cName)
 		}
 	} else {
 		// Create regular device node
-		err = syscallcompat.Mknodat(dirfd, cName, mode, int(dev))
-	}
-	if err != nil {
-		return fuse.ToStatus(err)
-	}
-	// Set owner
-	if fs.args.PreserveOwner {
-		err = syscallcompat.Fchownat(dirfd, cName, int(context.Owner.Uid),
-			int(context.Owner.Gid), unix.AT_SYMLINK_NOFOLLOW)
-		if err != nil {
-			tlog.Warn.Printf("Mknod: Fchownat failed: %v", err)
-		}
+		err = syscallcompat.MknodatUser(dirfd, cName, mode, int(dev), context)
 	}
-	return fuse.OK
+	return fuse.ToStatus(err)
 }
 
 // Truncate - FUSE call. Truncates a file.
diff --git a/internal/syscallcompat/sys_darwin.go b/internal/syscallcompat/sys_darwin.go
index 3c431b9..c9f3ad7 100644
--- a/internal/syscallcompat/sys_darwin.go
+++ b/internal/syscallcompat/sys_darwin.go
@@ -63,6 +63,11 @@ func Mknodat(dirfd int, path string, mode uint32, dev int) (err error) {
 	return emulateMknodat(dirfd, path, mode, dev)
 }
 
+func MknodatUser(dirfd int, path string, mode uint32, dev int, context *fuse.Context) (err error) {
+	// FIXME: take into account context.Owner
+	return Mknodat(dirfd, path, mode, dev)
+}
+
 func Fchmodat(dirfd int, path string, mode uint32, flags int) (err error) {
 	return emulateFchmodat(dirfd, path, mode, flags)
 }
diff --git a/internal/syscallcompat/sys_linux.go b/internal/syscallcompat/sys_linux.go
index a431195..cf747b1 100644
--- a/internal/syscallcompat/sys_linux.go
+++ b/internal/syscallcompat/sys_linux.go
@@ -113,6 +113,28 @@ func Mknodat(dirfd int, path string, mode uint32, dev int) (err error) {
 	return syscall.Mknodat(dirfd, path, mode, dev)
 }
 
+// MknodatUser runs the Mknodat syscall in the context of a different user.
+func MknodatUser(dirfd int, path string, mode uint32, dev int, context *fuse.Context) (err error) {
+	if context != nil {
+		runtime.LockOSThread()
+		defer runtime.UnlockOSThread()
+
+		err = syscall.Setregid(-1, int(context.Owner.Gid))
+		if err != nil {
+			return err
+		}
+		defer syscall.Setregid(-1, 0)
+
+		err = syscall.Setreuid(-1, int(context.Owner.Uid))
+		if err != nil {
+			return err
+		}
+		defer syscall.Setreuid(-1, 0)
+	}
+
+	return Mknodat(dirfd, path, mode, dev)
+}
+
 // Dup3 wraps the Dup3 syscall. We want to use Dup3 rather than Dup2 because Dup2
 // is not implemented on arm64.
 func Dup3(oldfd int, newfd int, flags int) (err error) {