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crypto/rand: use getrandom system call on Linux
Adds internal/syscall package. Fixes #8520 LGTM=r, agl R=agl, rsc, r CC=golang-codereviews, iant https://golang.org/cl/123260044
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39
src/pkg/crypto/rand/rand_linux.go
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39
src/pkg/crypto/rand/rand_linux.go
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@ -0,0 +1,39 @@
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// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package rand
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import (
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"internal/syscall"
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"sync"
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)
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func init() {
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altGetRandom = getRandomLinux
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}
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var (
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once sync.Once
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useSyscall bool
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)
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func pickStrategy() {
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// Test whether we should use the system call or /dev/urandom.
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// We'll fall back to urandom if:
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// - the kernel is too old (before 3.17)
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// - the machine has no entropy available (early boot + no hardware
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// entropy source?) and we want to avoid blocking later.
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var buf [1]byte
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n, err := syscall.GetRandom(buf[:], syscall.GRND_NONBLOCK)
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useSyscall = n == 1 && err == nil
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}
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func getRandomLinux(p []byte) (ok bool) {
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once.Do(pickStrategy)
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if !useSyscall {
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return false
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}
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n, err := syscall.GetRandom(p, 0)
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return n == len(p) && err == nil
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}
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@ -20,6 +20,8 @@ import (
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"time"
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)
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const urandomDevice = "/dev/urandom"
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// Easy implementation: read from /dev/urandom.
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// This is sufficient on Linux, OS X, and FreeBSD.
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@ -27,7 +29,7 @@ func init() {
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if runtime.GOOS == "plan9" {
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Reader = newReader(nil)
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} else {
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Reader = &devReader{name: "/dev/urandom"}
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Reader = &devReader{name: urandomDevice}
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}
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}
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@ -38,7 +40,14 @@ type devReader struct {
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mu sync.Mutex
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}
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// altGetRandom if non-nil specifies an OS-specific function to get
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// urandom-style randomness.
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var altGetRandom func([]byte) (ok bool)
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func (r *devReader) Read(b []byte) (n int, err error) {
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if altGetRandom != nil && r.name == urandomDevice && altGetRandom(b) {
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return len(b), nil
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}
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r.mu.Lock()
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defer r.mu.Unlock()
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if r.f == nil {
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@ -279,7 +279,7 @@ var pkgDeps = map[string][]string{
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// Random byte, number generation.
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// This would be part of core crypto except that it imports
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// math/big, which imports fmt.
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"crypto/rand": {"L4", "CRYPTO", "OS", "math/big", "syscall"},
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"crypto/rand": {"L4", "CRYPTO", "OS", "math/big", "syscall", "internal/syscall"},
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// Mathematical crypto: dependencies on fmt (L4) and math/big.
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// We could avoid some of the fmt, but math/big imports fmt anyway.
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55
src/pkg/internal/syscall/getrandom_linux.go
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55
src/pkg/internal/syscall/getrandom_linux.go
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@ -0,0 +1,55 @@
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// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package syscall
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import (
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"runtime"
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"sync/atomic"
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stdsyscall "syscall"
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"unsafe"
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)
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var randomTrap = map[string]uintptr{
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"amd64": 318,
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"386": 355,
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}[runtime.GOARCH]
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var randomUnsupported int32 // atomic
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// GetRandomFlag is a flag supported by the getrandom system call.
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type GetRandomFlag uintptr
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const (
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// GRND_NONBLOCK means return EAGAIN rather than blocking.
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GRND_NONBLOCK GetRandomFlag = 0x0001
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// GRND_RANDOM means use the /dev/random pool instead of /dev/urandom.
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GRND_RANDOM GetRandomFlag = 0x0002
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)
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// GetRandom calls the Linux getrandom system call.
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// See https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c6e9d6f38894798696f23c8084ca7edbf16ee895
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func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
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if randomTrap == 0 {
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return 0, stdsyscall.ENOSYS
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}
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if len(p) == 0 {
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return 0, nil
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}
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if atomic.LoadInt32(&randomUnsupported) != 0 {
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return 0, stdsyscall.ENOSYS
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}
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r1, _, errno := stdsyscall.Syscall(randomTrap,
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uintptr(unsafe.Pointer(&p[0])),
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uintptr(len(p)),
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uintptr(flags))
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if errno != 0 {
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if errno == stdsyscall.ENOSYS {
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atomic.StoreInt32(&randomUnsupported, 1)
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}
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return 0, errno
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}
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return int(r1), nil
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}
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