inet.af/netstack@v0.0.0-20220214151720-7585b01ddccf/rand/rand_linux.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 rand implements a cryptographically secure pseudorandom number
    16  // generator.
    17  package rand
    18  
    19  import (
    20  	"bufio"
    21  	"crypto/rand"
    22  	"io"
    23  
    24  	"golang.org/x/sys/unix"
    25  	"inet.af/netstack/sync"
    26  )
    27  
    28  // reader implements an io.Reader that returns pseudorandom bytes.
    29  type reader struct {
    30  	once         sync.Once
    31  	useGetrandom bool
    32  }
    33  
    34  // Read implements io.Reader.Read.
    35  func (r *reader) Read(p []byte) (int, error) {
    36  	r.once.Do(func() {
    37  		_, err := unix.Getrandom(p, 0)
    38  		if err != unix.ENOSYS {
    39  			r.useGetrandom = true
    40  		}
    41  	})
    42  
    43  	if r.useGetrandom {
    44  		return unix.Getrandom(p, 0)
    45  	}
    46  	return rand.Read(p)
    47  }
    48  
    49  // bufferedReader implements a threadsafe buffered io.Reader.
    50  type bufferedReader struct {
    51  	mu sync.Mutex
    52  	r  *bufio.Reader
    53  }
    54  
    55  // Read implements io.Reader.Read.
    56  func (b *bufferedReader) Read(p []byte) (int, error) {
    57  	b.mu.Lock()
    58  	n, err := b.r.Read(p)
    59  	b.mu.Unlock()
    60  	return n, err
    61  }
    62  
    63  // Reader is the default reader.
    64  var Reader io.Reader = &bufferedReader{r: bufio.NewReader(&reader{})}
    65  
    66  // Read reads from the default reader.
    67  func Read(b []byte) (int, error) {
    68  	return io.ReadFull(Reader, b)
    69  }
    70  
    71  // Init can be called to make sure /dev/urandom is pre-opened on kernels that
    72  // do not support getrandom(2).
    73  func Init() error {
    74  	p := make([]byte, 1)
    75  	_, err := Read(p)
    76  	return err
    77  }