Implement FUSE_CREATE

FUSE_CREATE is called when issuing creat(2) or open(2) with O_CREAT. It
creates a new file on the FUSE filesystem.

Fixes #3825

2 files changed, 60 insertions, 0 deletions

diff --git a/pkg/abi/linux/fuse.go b/pkg/abi/linux/fuse.go
index ed40df564..adc04dbcc 100644
--- a/pkg/abi/linux/fuse.go
+++ b/pkg/abi/linux/fuse.go
@@ -445,6 +445,48 @@ type FUSEReleaseIn struct {
 	LockOwner uint64
 }
 
+// FUSECreateMeta contains all the static fields of FUSECreateIn,
+// which is used for FUSE_CREATE.
+//
+// +marshal
+type FUSECreateMeta struct {
+	// Flags of the creating file.
+	Flags uint32
+
+	// Mode is the mode of the creating file.
+	Mode uint32
+
+	// Umask is the current file mode creation mask.
+	Umask uint32
+	_     uint32
+}
+
+// FUSECreateIn contains all the arguments sent by the kernel to the daemon, to
+// atomically create and open a new regular file.
+//
+// Dynamically-sized objects cannot be marshalled.
+type FUSECreateIn struct {
+	marshal.StubMarshallable
+
+	// CreateMeta contains mode, rdev and umash field for FUSE_MKNODS.
+	CreateMeta FUSECreateMeta
+
+	// Name is the name of the node to create.
+	Name string
+}
+
+// MarshalBytes serializes r.CreateMeta and r.Name to the dst buffer.
+func (r *FUSECreateIn) MarshalBytes(buf []byte) {
+	r.CreateMeta.MarshalBytes(buf[:r.CreateMeta.SizeBytes()])
+	copy(buf[r.CreateMeta.SizeBytes():], r.Name)
+}
+
+// SizeBytes is the size of the memory representation of FUSECreateIn.
+// 1 extra byte for null-terminated string.
+func (r *FUSECreateIn) SizeBytes() int {
+	return r.CreateMeta.SizeBytes() + len(r.Name) + 1
+}
+
 // FUSEMknodMeta contains all the static fields of FUSEMknodIn,
 // which is used for FUSE_MKNOD.
 //
diff --git a/pkg/sentry/fsimpl/fuse/fusefs.go b/pkg/sentry/fsimpl/fuse/fusefs.go
index e1bbb4b52..cfae9ed0d 100644
--- a/pkg/sentry/fsimpl/fuse/fusefs.go
+++ b/pkg/sentry/fsimpl/fuse/fusefs.go
@@ -392,6 +392,24 @@ func (inode) Valid(ctx context.Context) bool {
 	return true
 }
 
+// NewFile implements kernfs.Inode.NewFile.
+func (i *inode) NewFile(ctx context.Context, name string, opts vfs.OpenOptions) (*vfs.Dentry, error) {
+	kernelTask := kernel.TaskFromContext(ctx)
+	if kernelTask == nil {
+		log.Warningf("fusefs.Inode.NewFile: couldn't get kernel task from context", i.NodeID)
+		return nil, syserror.EINVAL
+	}
+	in := linux.FUSECreateIn{
+		CreateMeta: linux.FUSECreateMeta{
+			Flags: opts.Flags,
+			Mode:  uint32(opts.Mode) | linux.S_IFREG,
+			Umask: uint32(kernelTask.FSContext().Umask()),
+		},
+		Name: name,
+	}
+	return i.newEntry(ctx, name, linux.S_IFREG, linux.FUSE_CREATE, &in)
+}
+
 // NewNode implements kernfs.Inode.NewNode.
 func (i *inode) NewNode(ctx context.Context, name string, opts vfs.MknodOptions) (*vfs.Dentry, error) {
 	in := linux.FUSEMknodIn{