github.com/nicocha30/gvisor-ligolo@v0.0.0-20230726075806-989fa2c0a413/pkg/sentry/devices/memdev/zero.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  	"github.com/nicocha30/gvisor-ligolo/pkg/context"
    19  	"github.com/nicocha30/gvisor-ligolo/pkg/sentry/fsimpl/tmpfs"
    20  	"github.com/nicocha30/gvisor-ligolo/pkg/sentry/kernel"
    21  	"github.com/nicocha30/gvisor-ligolo/pkg/sentry/kernel/auth"
    22  	"github.com/nicocha30/gvisor-ligolo/pkg/sentry/memmap"
    23  	"github.com/nicocha30/gvisor-ligolo/pkg/sentry/vfs"
    24  	"github.com/nicocha30/gvisor-ligolo/pkg/usermem"
    25  )
    26  
    27  const zeroDevMinor = 5
    28  
    29  // zeroDevice implements vfs.Device for /dev/zero.
    30  //
    31  // +stateify savable
    32  type zeroDevice struct{}
    33  
    34  // Open implements vfs.Device.Open.
    35  func (zeroDevice) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
    36  	fd := &zeroFD{}
    37  	if err := fd.vfsfd.Init(fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{
    38  		UseDentryMetadata: true,
    39  	}); err != nil {
    40  		return nil, err
    41  	}
    42  	return &fd.vfsfd, nil
    43  }
    44  
    45  // zeroFD implements vfs.FileDescriptionImpl for /dev/zero.
    46  //
    47  // +stateify savable
    48  type zeroFD struct {
    49  	vfsfd vfs.FileDescription
    50  	vfs.FileDescriptionDefaultImpl
    51  	vfs.DentryMetadataFileDescriptionImpl
    52  	vfs.NoLockFD
    53  }
    54  
    55  // Release implements vfs.FileDescriptionImpl.Release.
    56  func (fd *zeroFD) Release(context.Context) {
    57  	// noop
    58  }
    59  
    60  // PRead implements vfs.FileDescriptionImpl.PRead.
    61  func (fd *zeroFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
    62  	return dst.ZeroOut(ctx, dst.NumBytes())
    63  }
    64  
    65  // Read implements vfs.FileDescriptionImpl.Read.
    66  func (fd *zeroFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
    67  	return dst.ZeroOut(ctx, dst.NumBytes())
    68  }
    69  
    70  // PWrite implements vfs.FileDescriptionImpl.PWrite.
    71  func (fd *zeroFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
    72  	return src.NumBytes(), nil
    73  }
    74  
    75  // Write implements vfs.FileDescriptionImpl.Write.
    76  func (fd *zeroFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
    77  	return src.NumBytes(), nil
    78  }
    79  
    80  // Seek implements vfs.FileDescriptionImpl.Seek.
    81  func (fd *zeroFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
    82  	return 0, nil
    83  }
    84  
    85  // ConfigureMMap implements vfs.FileDescriptionImpl.ConfigureMMap.
    86  func (fd *zeroFD) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
    87  	if opts.Private || !opts.MaxPerms.Write {
    88  		// This mapping will never permit writing to the "underlying file" (in
    89  		// Linux terms, it isn't VM_SHARED), so implement it as an anonymous
    90  		// mapping, but back it with fd; this is what Linux does, and is
    91  		// actually application-visible because the resulting VMA will show up
    92  		// in /proc/[pid]/maps with fd.vfsfd.VirtualDentry()'s path rather than
    93  		// "/dev/zero (deleted)".
    94  		opts.Offset = 0
    95  		opts.MappingIdentity = &fd.vfsfd
    96  		opts.SentryOwnedContent = true
    97  		opts.MappingIdentity.IncRef()
    98  		return nil
    99  	}
   100  	tmpfsFD, err := tmpfs.NewZeroFile(ctx, auth.CredentialsFromContext(ctx), kernel.KernelFromContext(ctx).ShmMount(), opts.Length)
   101  	if err != nil {
   102  		return err
   103  	}
   104  	defer tmpfsFD.DecRef(ctx)
   105  	return tmpfsFD.ConfigureMMap(ctx, opts)
   106  }