github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/syscalls/linux/vfs2/path.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 vfs2
    16  
    17  import (
    18  	"github.com/SagerNet/gvisor/pkg/abi/linux"
    19  	"github.com/SagerNet/gvisor/pkg/errors/linuxerr"
    20  	"github.com/SagerNet/gvisor/pkg/fspath"
    21  	"github.com/SagerNet/gvisor/pkg/hostarch"
    22  	"github.com/SagerNet/gvisor/pkg/sentry/kernel"
    23  	"github.com/SagerNet/gvisor/pkg/sentry/vfs"
    24  	"github.com/SagerNet/gvisor/pkg/syserror"
    25  )
    26  
    27  func copyInPath(t *kernel.Task, addr hostarch.Addr) (fspath.Path, error) {
    28  	pathname, err := t.CopyInString(addr, linux.PATH_MAX)
    29  	if err != nil {
    30  		return fspath.Path{}, err
    31  	}
    32  	return fspath.Parse(pathname), nil
    33  }
    34  
    35  type taskPathOperation struct {
    36  	pop          vfs.PathOperation
    37  	haveStartRef bool
    38  }
    39  
    40  func getTaskPathOperation(t *kernel.Task, dirfd int32, path fspath.Path, shouldAllowEmptyPath shouldAllowEmptyPath, shouldFollowFinalSymlink shouldFollowFinalSymlink) (taskPathOperation, error) {
    41  	root := t.FSContext().RootDirectoryVFS2()
    42  	start := root
    43  	haveStartRef := false
    44  	if !path.Absolute {
    45  		if !path.HasComponents() && !bool(shouldAllowEmptyPath) {
    46  			root.DecRef(t)
    47  			return taskPathOperation{}, syserror.ENOENT
    48  		}
    49  		if dirfd == linux.AT_FDCWD {
    50  			start = t.FSContext().WorkingDirectoryVFS2()
    51  			haveStartRef = true
    52  		} else {
    53  			dirfile := t.GetFileVFS2(dirfd)
    54  			if dirfile == nil {
    55  				root.DecRef(t)
    56  				return taskPathOperation{}, linuxerr.EBADF
    57  			}
    58  			start = dirfile.VirtualDentry()
    59  			start.IncRef()
    60  			haveStartRef = true
    61  			dirfile.DecRef(t)
    62  		}
    63  	}
    64  	return taskPathOperation{
    65  		pop: vfs.PathOperation{
    66  			Root:               root,
    67  			Start:              start,
    68  			Path:               path,
    69  			FollowFinalSymlink: bool(shouldFollowFinalSymlink),
    70  		},
    71  		haveStartRef: haveStartRef,
    72  	}, nil
    73  }
    74  
    75  func (tpop *taskPathOperation) Release(t *kernel.Task) {
    76  	tpop.pop.Root.DecRef(t)
    77  	if tpop.haveStartRef {
    78  		tpop.pop.Start.DecRef(t)
    79  		tpop.haveStartRef = false
    80  	}
    81  }
    82  
    83  type shouldAllowEmptyPath bool
    84  
    85  const (
    86  	disallowEmptyPath shouldAllowEmptyPath = false
    87  	allowEmptyPath    shouldAllowEmptyPath = true
    88  )
    89  
    90  type shouldFollowFinalSymlink bool
    91  
    92  const (
    93  	nofollowFinalSymlink shouldFollowFinalSymlink = false
    94  	followFinalSymlink   shouldFollowFinalSymlink = true
    95  )