github.com/nicocha30/gvisor-ligolo@v0.0.0-20230726075806-989fa2c0a413/pkg/fsutil/fsutil_unsafe.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 fsutil
    16  
    17  import (
    18  	"unsafe"
    19  
    20  	"golang.org/x/sys/unix"
    21  	"github.com/nicocha30/gvisor-ligolo/pkg/syserr"
    22  )
    23  
    24  // UnixDirentMaxSize is the maximum size of unix.Dirent in bytes.
    25  var UnixDirentMaxSize = int(unsafe.Sizeof(unix.Dirent{}))
    26  
    27  // Utimensat is a convenience wrapper to make the utimensat(2) syscall. It
    28  // additionally handles empty name.
    29  func Utimensat(dirFd int, name string, times [2]unix.Timespec, flags int) error {
    30  	// utimensat(2) doesn't accept empty name, instead name must be nil to make it
    31  	// operate directly on 'dirFd' unlike other *at syscalls.
    32  	var namePtr unsafe.Pointer
    33  	if name != "" {
    34  		nameBytes, err := unix.BytePtrFromString(name)
    35  		if err != nil {
    36  			return err
    37  		}
    38  		namePtr = unsafe.Pointer(nameBytes)
    39  	}
    40  
    41  	timesPtr := unsafe.Pointer(&times[0])
    42  
    43  	if _, _, errno := unix.Syscall6(
    44  		unix.SYS_UTIMENSAT,
    45  		uintptr(dirFd),
    46  		uintptr(namePtr),
    47  		uintptr(timesPtr),
    48  		uintptr(flags),
    49  		0,
    50  		0); errno != 0 {
    51  
    52  		return syserr.FromHost(errno).ToError()
    53  	}
    54  	return nil
    55  }
    56  
    57  // RenameAt is a convenience wrapper to make the renameat(2) syscall. It
    58  // additionally handles empty names.
    59  func RenameAt(oldDirFD int, oldName string, newDirFD int, newName string) error {
    60  	var oldNamePtr unsafe.Pointer
    61  	if oldName != "" {
    62  		nameBytes, err := unix.BytePtrFromString(oldName)
    63  		if err != nil {
    64  			return err
    65  		}
    66  		oldNamePtr = unsafe.Pointer(nameBytes)
    67  	}
    68  	var newNamePtr unsafe.Pointer
    69  	if newName != "" {
    70  		nameBytes, err := unix.BytePtrFromString(newName)
    71  		if err != nil {
    72  			return err
    73  		}
    74  		newNamePtr = unsafe.Pointer(nameBytes)
    75  	}
    76  
    77  	if _, _, errno := unix.Syscall6(
    78  		unix.SYS_RENAMEAT,
    79  		uintptr(oldDirFD),
    80  		uintptr(oldNamePtr),
    81  		uintptr(newDirFD),
    82  		uintptr(newNamePtr),
    83  		0,
    84  		0); errno != 0 {
    85  
    86  		return syserr.FromHost(errno).ToError()
    87  	}
    88  	return nil
    89  }
    90  
    91  // ParseDirents parses dirents from buf. buf must have been populated by
    92  // getdents64(2) syscall. It calls the handleDirent callback for each dirent.
    93  func ParseDirents(buf []byte, handleDirent func(ino uint64, off int64, ftype uint8, name string, reclen uint16) bool) {
    94  	for len(buf) > 0 {
    95  		// Interpret the buf populated by unix.Getdents as unix.Dirent.
    96  		dirent := *(*unix.Dirent)(unsafe.Pointer(&buf[0]))
    97  
    98  		// Advance buf for the next dirent.
    99  		buf = buf[dirent.Reclen:]
   100  
   101  		// Extracting the name is pretty tedious...
   102  		var nameBuf [unix.NAME_MAX]byte
   103  		var nameLen int
   104  		for i := 0; i < len(dirent.Name); i++ {
   105  			// The name is null terminated.
   106  			if dirent.Name[i] == 0 {
   107  				nameLen = i
   108  				break
   109  			}
   110  			nameBuf[i] = byte(dirent.Name[i])
   111  		}
   112  		name := string(nameBuf[:nameLen])
   113  
   114  		// Skip `.` and `..` entries. It is anyways ignored by the client. We also
   115  		// don't want to leak information about `..`.
   116  		if name == "." || name == ".." {
   117  			continue
   118  		}
   119  
   120  		// Deliver results to caller.
   121  		if !handleDirent(dirent.Ino, dirent.Off, dirent.Type, name, dirent.Reclen) {
   122  			return
   123  		}
   124  	}
   125  }