gvisor.dev/gvisor@v0.0.0-20240520182842-f9d4d51c7e0f/pkg/sentry/fsimpl/sockfs/sockfs.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 sockfs provides a filesystem implementation for anonymous sockets.
    16  package sockfs
    17  
    18  import (
    19  	"fmt"
    20  
    21  	"gvisor.dev/gvisor/pkg/abi/linux"
    22  	"gvisor.dev/gvisor/pkg/context"
    23  	"gvisor.dev/gvisor/pkg/errors/linuxerr"
    24  	"gvisor.dev/gvisor/pkg/fspath"
    25  	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
    26  	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
    27  	"gvisor.dev/gvisor/pkg/sentry/vfs"
    28  )
    29  
    30  // filesystemType implements vfs.FilesystemType.
    31  //
    32  // +stateify savable
    33  type filesystemType struct{}
    34  
    35  // GetFilesystem implements vfs.FilesystemType.GetFilesystem.
    36  func (fsType filesystemType) GetFilesystem(_ context.Context, vfsObj *vfs.VirtualFilesystem, _ *auth.Credentials, _ string, _ vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
    37  	panic("sockfs.filesystemType.GetFilesystem should never be called")
    38  }
    39  
    40  // Name implements vfs.FilesystemType.Name.
    41  //
    42  // Note that registering sockfs is unnecessary, except for the fact that it
    43  // will not show up under /proc/filesystems as a result. This is a very minor
    44  // discrepancy from Linux.
    45  func (filesystemType) Name() string {
    46  	return "sockfs"
    47  }
    48  
    49  // Release implements vfs.FilesystemType.Release.
    50  func (filesystemType) Release(ctx context.Context) {}
    51  
    52  // +stateify savable
    53  type filesystem struct {
    54  	kernfs.Filesystem
    55  
    56  	devMinor uint32
    57  }
    58  
    59  // NewFilesystem sets up and returns a new sockfs filesystem.
    60  //
    61  // Note that there should only ever be one instance of sockfs.Filesystem,
    62  // backing a global socket mount.
    63  func NewFilesystem(vfsObj *vfs.VirtualFilesystem) (*vfs.Filesystem, error) {
    64  	devMinor, err := vfsObj.GetAnonBlockDevMinor()
    65  	if err != nil {
    66  		return nil, err
    67  	}
    68  	fs := &filesystem{
    69  		devMinor: devMinor,
    70  	}
    71  	fs.Filesystem.VFSFilesystem().Init(vfsObj, filesystemType{}, fs)
    72  	return fs.Filesystem.VFSFilesystem(), nil
    73  }
    74  
    75  // Release implements vfs.FilesystemImpl.Release.
    76  func (fs *filesystem) Release(ctx context.Context) {
    77  	fs.Filesystem.VFSFilesystem().VirtualFilesystem().PutAnonBlockDevMinor(fs.devMinor)
    78  	fs.Filesystem.Release(ctx)
    79  }
    80  
    81  // PrependPath implements vfs.FilesystemImpl.PrependPath.
    82  func (fs *filesystem) PrependPath(ctx context.Context, vfsroot, vd vfs.VirtualDentry, b *fspath.Builder) error {
    83  	inode := vd.Dentry().Impl().(*kernfs.Dentry).Inode().(*inode)
    84  	b.PrependComponent(fmt.Sprintf("socket:[%d]", inode.InodeAttrs.Ino()))
    85  	return vfs.PrependPathSyntheticError{}
    86  }
    87  
    88  // MountOptions implements vfs.FilesystemImpl.MountOptions.
    89  func (fs *filesystem) MountOptions() string {
    90  	return ""
    91  }
    92  
    93  // inode implements kernfs.Inode.
    94  //
    95  // +stateify savable
    96  type inode struct {
    97  	kernfs.InodeAnonymous
    98  	kernfs.InodeAttrs
    99  	kernfs.InodeNoopRefCount
   100  	kernfs.InodeNotDirectory
   101  	kernfs.InodeNotSymlink
   102  	kernfs.InodeWatches
   103  }
   104  
   105  // Open implements kernfs.Inode.Open.
   106  func (i *inode) Open(ctx context.Context, rp *vfs.ResolvingPath, d *kernfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
   107  	return nil, linuxerr.ENXIO
   108  }
   109  
   110  // StatFS implements kernfs.Inode.StatFS.
   111  func (i *inode) StatFS(ctx context.Context, fs *vfs.Filesystem) (linux.Statfs, error) {
   112  	return vfs.GenericStatFS(linux.SOCKFS_MAGIC), nil
   113  }
   114  
   115  // NewDentry constructs and returns a sockfs dentry.
   116  //
   117  // Preconditions: mnt.Filesystem() must have been returned by NewFilesystem().
   118  func NewDentry(ctx context.Context, mnt *vfs.Mount) *vfs.Dentry {
   119  	fs := mnt.Filesystem().Impl().(*filesystem)
   120  
   121  	// File mode matches net/socket.c:sock_alloc.
   122  	filemode := linux.FileMode(linux.S_IFSOCK | 0777)
   123  	i := &inode{}
   124  	i.InodeAttrs.Init(ctx, auth.CredentialsFromContext(ctx), linux.UNNAMED_MAJOR, fs.devMinor, fs.Filesystem.NextIno(), filemode)
   125  
   126  	d := &kernfs.Dentry{}
   127  	d.Init(&fs.Filesystem, i)
   128  	return d.VFSDentry()
   129  }