github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/fs/inotify_event.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 fs
    16  
    17  import (
    18  	"bytes"
    19  	"fmt"
    20  
    21  	"github.com/SagerNet/gvisor/pkg/context"
    22  	"github.com/SagerNet/gvisor/pkg/hostarch"
    23  	"github.com/SagerNet/gvisor/pkg/usermem"
    24  )
    25  
    26  // inotifyEventBaseSize is the base size of linux's struct inotify_event. This
    27  // must be a power 2 for rounding below.
    28  const inotifyEventBaseSize = 16
    29  
    30  // Event represents a struct inotify_event from linux.
    31  //
    32  // +stateify savable
    33  type Event struct {
    34  	eventEntry
    35  
    36  	wd     int32
    37  	mask   uint32
    38  	cookie uint32
    39  
    40  	// len is computed based on the name field is set automatically by
    41  	// Event.setName. It should be 0 when no name is set; otherwise it is the
    42  	// length of the name slice.
    43  	len uint32
    44  
    45  	// The name field has special padding requirements and should only be set by
    46  	// calling Event.setName.
    47  	name []byte
    48  }
    49  
    50  func newEvent(wd int32, name string, events, cookie uint32) *Event {
    51  	e := &Event{
    52  		wd:     wd,
    53  		mask:   events,
    54  		cookie: cookie,
    55  	}
    56  	if name != "" {
    57  		e.setName(name)
    58  	}
    59  	return e
    60  }
    61  
    62  // paddedBytes converts a go string to a null-terminated c-string, padded with
    63  // null bytes to a total size of 'l'. 'l' must be large enough for all the bytes
    64  // in the 's' plus at least one null byte.
    65  func paddedBytes(s string, l uint32) []byte {
    66  	if l < uint32(len(s)+1) {
    67  		panic("Converting string to byte array results in truncation, this can lead to buffer-overflow due to the missing null-byte!")
    68  	}
    69  	b := make([]byte, l)
    70  	copy(b, s)
    71  
    72  	// b was zero-value initialized during make(), so the rest of the slice is
    73  	// already filled with null bytes.
    74  
    75  	return b
    76  }
    77  
    78  // setName sets the optional name for this event.
    79  func (e *Event) setName(name string) {
    80  	// We need to pad the name such that the entire event length ends up a
    81  	// multiple of inotifyEventBaseSize.
    82  	unpaddedLen := len(name) + 1
    83  	// Round up to nearest multiple of inotifyEventBaseSize.
    84  	e.len = uint32((unpaddedLen + inotifyEventBaseSize - 1) & ^(inotifyEventBaseSize - 1))
    85  	// Make sure we haven't overflowed and wrapped around when rounding.
    86  	if unpaddedLen > int(e.len) {
    87  		panic("Overflow when rounding inotify event size, the 'name' field was too big.")
    88  	}
    89  	e.name = paddedBytes(name, e.len)
    90  }
    91  
    92  func (e *Event) sizeOf() int {
    93  	s := inotifyEventBaseSize + int(e.len)
    94  	if s < inotifyEventBaseSize {
    95  		panic("overflow")
    96  	}
    97  	return s
    98  }
    99  
   100  // CopyTo serializes this event to dst. buf is used as a scratch buffer to
   101  // construct the output. We use a buffer allocated ahead of time for
   102  // performance. buf must be at least inotifyEventBaseSize bytes.
   103  func (e *Event) CopyTo(ctx context.Context, buf []byte, dst usermem.IOSequence) (int64, error) {
   104  	hostarch.ByteOrder.PutUint32(buf[0:], uint32(e.wd))
   105  	hostarch.ByteOrder.PutUint32(buf[4:], e.mask)
   106  	hostarch.ByteOrder.PutUint32(buf[8:], e.cookie)
   107  	hostarch.ByteOrder.PutUint32(buf[12:], e.len)
   108  
   109  	writeLen := 0
   110  
   111  	n, err := dst.CopyOut(ctx, buf)
   112  	if err != nil {
   113  		return 0, err
   114  	}
   115  	writeLen += n
   116  	dst = dst.DropFirst(n)
   117  
   118  	if e.len > 0 {
   119  		n, err = dst.CopyOut(ctx, e.name)
   120  		if err != nil {
   121  			return 0, err
   122  		}
   123  		writeLen += n
   124  	}
   125  
   126  	// Santiy check.
   127  	if writeLen != e.sizeOf() {
   128  		panic(fmt.Sprintf("Serialized unexpected amount of data for an event, expected %v, wrote %v.", e.sizeOf(), writeLen))
   129  	}
   130  
   131  	return int64(writeLen), nil
   132  }
   133  
   134  func (e *Event) equals(other *Event) bool {
   135  	return e.wd == other.wd &&
   136  		e.mask == other.mask &&
   137  		e.cookie == other.cookie &&
   138  		e.len == other.len &&
   139  		bytes.Equal(e.name, other.name)
   140  }