github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/devices/memdev/random.go (about)

     1  // Copyright 2020 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package memdev
    16  
    17  import (
    18  	"sync/atomic"
    19  
    20  	"github.com/SagerNet/gvisor/pkg/context"
    21  	"github.com/SagerNet/gvisor/pkg/rand"
    22  	"github.com/SagerNet/gvisor/pkg/safemem"
    23  	"github.com/SagerNet/gvisor/pkg/sentry/vfs"
    24  	"github.com/SagerNet/gvisor/pkg/usermem"
    25  )
    26  
    27  const (
    28  	randomDevMinor  = 8
    29  	urandomDevMinor = 9
    30  )
    31  
    32  // randomDevice implements vfs.Device for /dev/random and /dev/urandom.
    33  //
    34  // +stateify savable
    35  type randomDevice struct{}
    36  
    37  // Open implements vfs.Device.Open.
    38  func (randomDevice) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
    39  	fd := &randomFD{}
    40  	if err := fd.vfsfd.Init(fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{
    41  		UseDentryMetadata: true,
    42  	}); err != nil {
    43  		return nil, err
    44  	}
    45  	return &fd.vfsfd, nil
    46  }
    47  
    48  // randomFD implements vfs.FileDescriptionImpl for /dev/random.
    49  //
    50  // +stateify savable
    51  type randomFD struct {
    52  	vfsfd vfs.FileDescription
    53  	vfs.FileDescriptionDefaultImpl
    54  	vfs.DentryMetadataFileDescriptionImpl
    55  	vfs.NoLockFD
    56  
    57  	// off is the "file offset". off is accessed using atomic memory
    58  	// operations.
    59  	off int64
    60  }
    61  
    62  // Release implements vfs.FileDescriptionImpl.Release.
    63  func (fd *randomFD) Release(context.Context) {
    64  	// noop
    65  }
    66  
    67  // PRead implements vfs.FileDescriptionImpl.PRead.
    68  func (fd *randomFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
    69  	return dst.CopyOutFrom(ctx, safemem.FromIOReader{rand.Reader})
    70  }
    71  
    72  // Read implements vfs.FileDescriptionImpl.Read.
    73  func (fd *randomFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
    74  	n, err := dst.CopyOutFrom(ctx, safemem.FromIOReader{rand.Reader})
    75  	atomic.AddInt64(&fd.off, n)
    76  	return n, err
    77  }
    78  
    79  // PWrite implements vfs.FileDescriptionImpl.PWrite.
    80  func (fd *randomFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
    81  	// In Linux, this mixes the written bytes into the entropy pool; we just
    82  	// throw them away.
    83  	return src.NumBytes(), nil
    84  }
    85  
    86  // Write implements vfs.FileDescriptionImpl.Write.
    87  func (fd *randomFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
    88  	atomic.AddInt64(&fd.off, src.NumBytes())
    89  	return src.NumBytes(), nil
    90  }
    91  
    92  // Seek implements vfs.FileDescriptionImpl.Seek.
    93  func (fd *randomFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
    94  	// Linux: drivers/char/random.c:random_fops.llseek == urandom_fops.llseek
    95  	// == noop_llseek
    96  	return atomic.LoadInt64(&fd.off), nil
    97  }