Implement FUSE_MKNOD

Fixes #3492

2 files changed, 56 insertions, 0 deletions

diff --git a/pkg/abi/linux/fuse.go b/pkg/abi/linux/fuse.go
index a1b2a2abf..97d960096 100644
--- a/pkg/abi/linux/fuse.go
+++ b/pkg/abi/linux/fuse.go
@@ -413,3 +413,46 @@ type FUSEReleaseIn struct {
 	// LockOwner is the id of the lock owner if there is one.
 	LockOwner uint64
 }
+
+// FUSEMknodMeta contains all the static fields of FUSEMknodIn,
+// which is used for FUSE_MKNOD.
+//
+// +marshal
+type FUSEMknodMeta struct {
+	// Mode of the inode to create.
+	Mode uint32
+
+	// Rdev encodes device major and minor information.
+	Rdev uint32
+
+	// Umask is the current file mode creation mask.
+	Umask uint32
+
+	_ uint32
+}
+
+// FUSEMknodIn contains all the arguments sent by the kernel
+// to the daemon, to create a new file node.
+//
+// Dynamically-sized objects cannot be marshalled.
+type FUSEMknodIn struct {
+	marshal.StubMarshallable
+
+	// MknodMeta contains mode, rdev and umash field for FUSE_MKNODS.
+	MknodMeta FUSEMknodMeta
+
+	// Name is the name of the node to create.
+	Name string
+}
+
+// MarshalUnsafe serializes r.MknodMeta and r.Name to the dst buffer.
+func (r *FUSEMknodIn) MarshalUnsafe(buf []byte) {
+	r.MknodMeta.MarshalUnsafe(buf[:r.MknodMeta.SizeBytes()])
+	copy(buf[r.MknodMeta.SizeBytes():], r.Name)
+}
+
+// SizeBytes is the size of the memory representation of FUSEMknodIn.
+// 1 extra byte for null-terminated string.
+func (r *FUSEMknodIn) SizeBytes() int {
+	return r.MknodMeta.SizeBytes() + len(r.Name) + 1
+}
diff --git a/pkg/sentry/fsimpl/fuse/fusefs.go b/pkg/sentry/fsimpl/fuse/fusefs.go
index b5f05b80b..5cef0b94f 100644
--- a/pkg/sentry/fsimpl/fuse/fusefs.go
+++ b/pkg/sentry/fsimpl/fuse/fusefs.go
@@ -349,6 +349,19 @@ func (inode) Valid(ctx context.Context) bool {
 	return true
 }
 
+// NewNode implements kernfs.Inode.NewNode.
+func (i *inode) NewNode(ctx context.Context, name string, opts vfs.MknodOptions) (*vfs.Dentry, error) {
+	in := linux.FUSEMknodIn{
+		MknodMeta: linux.FUSEMknodMeta{
+			Mode:  uint32(opts.Mode),
+			Rdev:  linux.MakeDeviceID(uint16(opts.DevMajor), opts.DevMinor),
+			Umask: uint32(kernel.TaskFromContext(ctx).FSContext().Umask()),
+		},
+		Name: name,
+	}
+	return i.newEntry(ctx, name, opts.Mode.FileType(), linux.FUSE_MKNOD, &in)
+}
+
 // newEntry calls FUSE server for entry creation and allocates corresponding entry according to response.
 // Shared by FUSE_MKNOD, FUSE_MKDIR, FUSE_SYMLINK, FUSE_LINK and FUSE_LOOKUP.
 func (i *inode) newEntry(ctx context.Context, name string, fileType linux.FileMode, opcode linux.FUSEOpcode, payload marshal.Marshallable) (*vfs.Dentry, error) {