github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/fs/ramfs/symlink.go (about)

     1  // Copyright 2018 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 ramfs
    16  
    17  import (
    18  	"github.com/SagerNet/gvisor/pkg/abi/linux"
    19  	"github.com/SagerNet/gvisor/pkg/context"
    20  	"github.com/SagerNet/gvisor/pkg/sentry/fs"
    21  	"github.com/SagerNet/gvisor/pkg/sentry/fs/fsutil"
    22  	"github.com/SagerNet/gvisor/pkg/waiter"
    23  )
    24  
    25  // Symlink represents a symlink.
    26  //
    27  // +stateify savable
    28  type Symlink struct {
    29  	fsutil.InodeGenericChecker `state:"nosave"`
    30  	fsutil.InodeNoopRelease    `state:"nosave"`
    31  	fsutil.InodeNoopWriteOut   `state:"nosave"`
    32  	fsutil.InodeNotAllocatable `state:"nosave"`
    33  	fsutil.InodeNotDirectory   `state:"nosave"`
    34  	fsutil.InodeNotMappable    `state:"nosave"`
    35  	fsutil.InodeNotSocket      `state:"nosave"`
    36  	fsutil.InodeNotTruncatable `state:"nosave"`
    37  	fsutil.InodeVirtual        `state:"nosave"`
    38  
    39  	fsutil.InodeSimpleAttributes
    40  	fsutil.InodeSimpleExtendedAttributes
    41  
    42  	// Target is the symlink target.
    43  	Target string
    44  }
    45  
    46  var _ fs.InodeOperations = (*Symlink)(nil)
    47  
    48  // NewSymlink returns a new Symlink.
    49  func NewSymlink(ctx context.Context, owner fs.FileOwner, target string) *Symlink {
    50  	// A symlink is assumed to always have permissions 0777.
    51  	return &Symlink{
    52  		InodeSimpleAttributes: fsutil.NewInodeSimpleAttributes(ctx, owner, fs.FilePermsFromMode(0777), linux.RAMFS_MAGIC),
    53  		Target:                target,
    54  	}
    55  }
    56  
    57  // UnstableAttr returns all attributes of this ramfs symlink.
    58  func (s *Symlink) UnstableAttr(ctx context.Context, inode *fs.Inode) (fs.UnstableAttr, error) {
    59  	uattr, err := s.InodeSimpleAttributes.UnstableAttr(ctx, inode)
    60  	if err != nil {
    61  		return fs.UnstableAttr{}, err
    62  	}
    63  	uattr.Size = int64(len(s.Target))
    64  	uattr.Usage = uattr.Size
    65  	return uattr, nil
    66  }
    67  
    68  // SetPermissions on a symlink is always rejected.
    69  func (s *Symlink) SetPermissions(context.Context, *fs.Inode, fs.FilePermissions) bool {
    70  	return false
    71  }
    72  
    73  // Readlink reads the symlink value.
    74  func (s *Symlink) Readlink(ctx context.Context, _ *fs.Inode) (string, error) {
    75  	s.NotifyAccess(ctx)
    76  	return s.Target, nil
    77  }
    78  
    79  // Getlink returns ErrResolveViaReadlink, falling back to walking to the result
    80  // of Readlink().
    81  func (*Symlink) Getlink(context.Context, *fs.Inode) (*fs.Dirent, error) {
    82  	return nil, fs.ErrResolveViaReadlink
    83  }
    84  
    85  // GetFile implements fs.FileOperations.GetFile.
    86  func (s *Symlink) GetFile(ctx context.Context, dirent *fs.Dirent, flags fs.FileFlags) (*fs.File, error) {
    87  	return fs.NewFile(ctx, dirent, flags, &symlinkFileOperations{}), nil
    88  }
    89  
    90  // +stateify savable
    91  type symlinkFileOperations struct {
    92  	fsutil.FileNoIoctl              `state:"nosave"`
    93  	fsutil.FileNoMMap               `state:"nosave"`
    94  	fsutil.FileNoRead               `state:"nosave"`
    95  	fsutil.FileNoSeek               `state:"nosave"`
    96  	fsutil.FileNoSplice             `state:"nosave"`
    97  	fsutil.FileNoWrite              `state:"nosave"`
    98  	fsutil.FileNoopFlush            `state:"nosave"`
    99  	fsutil.FileNoopFsync            `state:"nosave"`
   100  	fsutil.FileNoopRelease          `state:"nosave"`
   101  	fsutil.FileNotDirReaddir        `state:"nosave"`
   102  	fsutil.FileUseInodeUnstableAttr `state:"nosave"`
   103  	waiter.AlwaysReady              `state:"nosave"`
   104  }
   105  
   106  var _ fs.FileOperations = (*symlinkFileOperations)(nil)