1 files changed, 93 insertions, 0 deletions
diff --git a/pkg/sentry/devices/memdev/random.go b/pkg/sentry/devices/memdev/random.go
new file mode 100644
index 000000000..5e7fe0280
--- /dev/null
+++ b/pkg/sentry/devices/memdev/random.go
@@ -0,0 +1,93 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package memdev
+
+import (
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/rand"
+	"gvisor.dev/gvisor/pkg/safemem"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+const (
+	randomDevMinor  = 8
+	urandomDevMinor = 9
+)
+
+// randomDevice implements vfs.Device for /dev/random and /dev/urandom.
+type randomDevice struct{}
+
+// Open implements vfs.Device.Open.
+func (randomDevice) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	fd := &randomFD{}
+	if err := fd.vfsfd.Init(fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{
+		UseDentryMetadata: true,
+	}); err != nil {
+		return nil, err
+	}
+	return &fd.vfsfd, nil
+}
+
+// randomFD implements vfs.FileDescriptionImpl for /dev/random.
+type randomFD struct {
+	vfsfd vfs.FileDescription
+	vfs.FileDescriptionDefaultImpl
+	vfs.DentryMetadataFileDescriptionImpl
+	vfs.NoLockFD
+
+	// off is the "file offset". off is accessed using atomic memory
+	// operations.
+	off int64
+}
+
+// Release implements vfs.FileDescriptionImpl.Release.
+func (fd *randomFD) Release(context.Context) {
+	// noop
+}
+
+// PRead implements vfs.FileDescriptionImpl.PRead.
+func (fd *randomFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
+	return dst.CopyOutFrom(ctx, safemem.FromIOReader{rand.Reader})
+}
+
+// Read implements vfs.FileDescriptionImpl.Read.
+func (fd *randomFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
+	n, err := dst.CopyOutFrom(ctx, safemem.FromIOReader{rand.Reader})
+	atomic.AddInt64(&fd.off, n)
+	return n, err
+}
+
+// PWrite implements vfs.FileDescriptionImpl.PWrite.
+func (fd *randomFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
+	// In Linux, this mixes the written bytes into the entropy pool; we just
+	// throw them away.
+	return src.NumBytes(), nil
+}
+
+// Write implements vfs.FileDescriptionImpl.Write.
+func (fd *randomFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
+	atomic.AddInt64(&fd.off, src.NumBytes())
+	return src.NumBytes(), nil
+}
+
+// Seek implements vfs.FileDescriptionImpl.Seek.
+func (fd *randomFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
+	// Linux: drivers/char/random.c:random_fops.llseek == urandom_fops.llseek
+	// == noop_llseek
+	return atomic.LoadInt64(&fd.off), nil
+}