gvisor.dev/gvisor@v0.0.0-20240520182842-f9d4d51c7e0f/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  	"gvisor.dev/gvisor/pkg/atomicbitops"
    19  	"gvisor.dev/gvisor/pkg/context"
    20  	"gvisor.dev/gvisor/pkg/rand"
    21  	"gvisor.dev/gvisor/pkg/safemem"
    22  	"gvisor.dev/gvisor/pkg/sentry/vfs"
    23  	"gvisor.dev/gvisor/pkg/usermem"
    24  )
    25  
    26  const (
    27  	randomDevMinor  = 8
    28  	urandomDevMinor = 9
    29  )
    30  
    31  // randomDevice implements vfs.Device for /dev/random and /dev/urandom.
    32  //
    33  // +stateify savable
    34  type randomDevice struct{}
    35  
    36  // Open implements vfs.Device.Open.
    37  func (randomDevice) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
    38  	fd := &randomFD{}
    39  	if err := fd.vfsfd.Init(fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{
    40  		UseDentryMetadata: true,
    41  	}); err != nil {
    42  		return nil, err
    43  	}
    44  	return &fd.vfsfd, nil
    45  }
    46  
    47  // randomFD implements vfs.FileDescriptionImpl for /dev/random.
    48  //
    49  // +stateify savable
    50  type randomFD struct {
    51  	vfsfd vfs.FileDescription
    52  	vfs.FileDescriptionDefaultImpl
    53  	vfs.DentryMetadataFileDescriptionImpl
    54  	vfs.NoLockFD
    55  
    56  	// off is the "file offset". off is accessed using atomic memory
    57  	// operations.
    58  	off atomicbitops.Int64
    59  }
    60  
    61  // Release implements vfs.FileDescriptionImpl.Release.
    62  func (fd *randomFD) Release(context.Context) {
    63  	// noop
    64  }
    65  
    66  // PRead implements vfs.FileDescriptionImpl.PRead.
    67  func (fd *randomFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
    68  	return dst.CopyOutFrom(ctx, safemem.FromIOReader{rand.Reader})
    69  }
    70  
    71  // Read implements vfs.FileDescriptionImpl.Read.
    72  func (fd *randomFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
    73  	n, err := dst.CopyOutFrom(ctx, safemem.FromIOReader{rand.Reader})
    74  	fd.off.Add(n)
    75  	return n, err
    76  }
    77  
    78  // PWrite implements vfs.FileDescriptionImpl.PWrite.
    79  func (fd *randomFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
    80  	// In Linux, this mixes the written bytes into the entropy pool; we just
    81  	// throw them away.
    82  	return src.NumBytes(), nil
    83  }
    84  
    85  // Write implements vfs.FileDescriptionImpl.Write.
    86  func (fd *randomFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
    87  	fd.off.Add(src.NumBytes())
    88  	return src.NumBytes(), nil
    89  }
    90  
    91  // Seek implements vfs.FileDescriptionImpl.Seek.
    92  func (fd *randomFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
    93  	// Linux: drivers/char/random.c:random_fops.llseek == urandom_fops.llseek
    94  	// == noop_llseek
    95  	return fd.off.Load(), nil
    96  }