mirror of
https://github.com/golang/go
synced 2024-11-18 14:04:45 -07:00
crypto/rand: use blocking getrandom call on Linux when supported
By changing getRandomLinux to immediately use the getrandom() syscall without GRND_NONBLOCK, we now only fall back to reading from /dev/urandom on Linux if the kernel does not support the getrandom() syscall. This means reads for crypto/rand will now block if the kernel has insufficient entropy on Linux kernels after v3.16. Before, if the kernel had insufficient entropy, it would fall back to reading from /dev/urandom. This would potentially return predictable data. Fixes #19274 Change-Id: I1cb081ce2f3096f18ad2820e52ecdbd993dc2afc Reviewed-on: https://go-review.googlesource.com/43852 Reviewed-by: Filippo Valsorda <hi@filippo.io> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
parent
f3f29d1dea
commit
95d991d30c
@ -6,34 +6,20 @@ package rand
|
|||||||
|
|
||||||
import (
|
import (
|
||||||
"internal/syscall/unix"
|
"internal/syscall/unix"
|
||||||
"sync"
|
|
||||||
)
|
)
|
||||||
|
|
||||||
func init() {
|
func init() {
|
||||||
altGetRandom = getRandomLinux
|
altGetRandom = getRandomLinux
|
||||||
}
|
}
|
||||||
|
|
||||||
var (
|
// If the kernel is too old (before 3.17) to support the getrandom syscall(),
|
||||||
once sync.Once
|
// unix.GetRandom will immediately return ENOSYS and we will then fall back to
|
||||||
useSyscall bool
|
// reading from /dev/urandom in rand_unix.go. unix.GetRandom caches the ENOSYS
|
||||||
)
|
// result so we only suffer the syscall overhead once in this case.
|
||||||
|
// If the kernel supports the getrandom() syscall, unix.GetRandom will block
|
||||||
func pickStrategy() {
|
// until the kernel has sufficient randomness (as we don't use GRND_NONBLOCK).
|
||||||
// Test whether we should use the system call or /dev/urandom.
|
// In this case, unix.GetRandom will not return an error.
|
||||||
// We'll fall back to urandom if:
|
|
||||||
// - the kernel is too old (before 3.17)
|
|
||||||
// - the machine has no entropy available (early boot + no hardware
|
|
||||||
// entropy source?) and we want to avoid blocking later.
|
|
||||||
var buf [1]byte
|
|
||||||
n, err := unix.GetRandom(buf[:], unix.GRND_NONBLOCK)
|
|
||||||
useSyscall = n == 1 && err == nil
|
|
||||||
}
|
|
||||||
|
|
||||||
func getRandomLinux(p []byte) (ok bool) {
|
func getRandomLinux(p []byte) (ok bool) {
|
||||||
once.Do(pickStrategy)
|
|
||||||
if !useSyscall {
|
|
||||||
return false
|
|
||||||
}
|
|
||||||
n, err := unix.GetRandom(p, 0)
|
n, err := unix.GetRandom(p, 0)
|
||||||
return n == len(p) && err == nil
|
return n == len(p) && err == nil
|
||||||
}
|
}
|
||||||
|
Loading…
Reference in New Issue
Block a user