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Document use of /dev/urandom vs /dev/random (#311)

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Also, on platforms where the devices are the same, prefer using
/dev/urandom.

Documentation of the devices being the same:
- macOS [`random(4)`](https://www.unix.com/man-page/mojave/4/urandom/)
- DragonFly [`getrandom(2)`](https://leaf.dragonflybsd.org/cgi/web-man?command=getrandom)
- Haiku [implementation](https://github.com/haiku/haiku/blob/f40bacae87f37276be7d107a6b3d41ca97b4d82c/src/add-ons/kernel/bus_managers/random/driver.cpp#L217-L222)

Signed-off-by: Joe Richey <joerichey@google.com>

Signed-off-by: Joe Richey <joerichey@google.com>
This commit is contained in:
Joseph Richey
2022-10-23 13:26:32 -07:00
committed by GitHub
parent 88d0d31a2c
commit d87d3399bb
2 changed files with 15 additions and 10 deletions
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src/lib.rs
+5 -5
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@@ -14,21 +14,21 @@
//! | ----------------- | ------------------ | --------------
//! | Linux, Android | `*‑linux‑*` | [`getrandom`][1] system call if available, otherwise [`/dev/urandom`][2] after successfully polling `/dev/random`
//! | Windows | `*‑windows‑*` | [`BCryptGenRandom`]
//! | macOS | `*‑apple‑darwin` | [`getentropy`][3] if available, otherwise [`/dev/random`][4] (identical to `/dev/urandom`)
//! | macOS | `*‑apple‑darwin` | [`getentropy`][3] if available, otherwise [`/dev/urandom`][4] (identical to `/dev/random`)
//! | iOS | `*‑apple‑ios` | [`SecRandomCopyBytes`]
//! | FreeBSD | `*‑freebsd` | [`getrandom`][5] if available, otherwise [`kern.arandom`][6]
//! | OpenBSD | `*‑openbsd` | [`getentropy`][7]
//! | NetBSD | `*‑netbsd` | [`kern.arandom`][8]
//! | Dragonfly BSD | `*‑dragonfly` | [`getrandom`][9] if available, otherwise [`/dev/random`][10]
//! | Dragonfly BSD | `*‑dragonfly` | [`getrandom`][9] if available, otherwise [`/dev/urandom`][10] (identical to `/dev/random`)
//! | Solaris, illumos | `*‑solaris`, `*‑illumos` | [`getrandom`][11] if available, otherwise [`/dev/random`][12]
//! | Fuchsia OS | `*‑fuchsia` | [`cprng_draw`]
//! | Redox | `*‑redox` | `/dev/urandom`
//! | Haiku | `*‑haiku` | `/dev/random` (identical to `/dev/urandom`)
//! | Haiku | `*‑haiku` | `/dev/urandom` (identical to `/dev/random`)
//! | Hermit | `x86_64-*-hermit` | [`RDRAND`]
//! | SGX | `x86_64‑*‑sgx` | [`RDRAND`]
//! | VxWorks | `*‑wrs‑vxworks‑*` | `randABytes` after checking entropy pool initialization with `randSecure`
//! | ESP-IDF | `*‑espidf` | [`esp_fill_random`]
//! | Emscripten | `*‑emscripten` | `/dev/random` (identical to `/dev/urandom`)
//! | Emscripten | `*‑emscripten` | `/dev/urandom` (identical to `/dev/random`)
//! | WASI | `wasm32‑wasi` | [`random_get`]
//! | Web Browser and Node.js | `wasm32‑*‑unknown` | [`Crypto.getRandomValues`] if available, then [`crypto.randomFillSync`] if on Node.js, see [WebAssembly support]
//! | SOLID | `*-kmc-solid_*` | `SOLID_RNG_SampleRandomBytes`
@@ -150,7 +150,7 @@
//! [1]: http://man7.org/linux/man-pages/man2/getrandom.2.html
//! [2]: http://man7.org/linux/man-pages/man4/urandom.4.html
//! [3]: https://www.unix.com/man-page/mojave/2/getentropy/
//! [4]: https://www.unix.com/man-page/mojave/4/random/
//! [4]: https://www.unix.com/man-page/mojave/4/urandom/
//! [5]: https://www.freebsd.org/cgi/man.cgi?query=getrandom&manpath=FreeBSD+12.0-stable
//! [6]: https://www.freebsd.org/cgi/man.cgi?query=random&sektion=4
//! [7]: https://man.openbsd.org/getentropy.2
src/use_file.rs
+10 -5
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@@ -18,16 +18,21 @@ use core::{
sync::atomic::{AtomicUsize, Ordering::Relaxed},
};
// We prefer using /dev/urandom and only use /dev/random if the OS
// documentation indicates that /dev/urandom is insecure.
// On Solaris/Illumos, see src/solaris_illumos.rs
// On Dragonfly, Haiku, and macOS, the devices are identical.
#[cfg(any(target_os = "solaris", target_os = "illumos"))]
const FILE_PATH: &str = "/dev/random\0";
#[cfg(any(
target_os = "android",
target_os = "linux",
target_os = "redox",
target_os = "dragonfly",
target_os = "emscripten",
target_os = "haiku",
target_os = "macos",
target_os = "solaris",
target_os = "illumos"
target_os = "macos"
))]
const FILE_PATH: &str = "/dev/random\0";
#[cfg(any(target_os = "android", target_os = "linux", target_os = "redox"))]
const FILE_PATH: &str = "/dev/urandom\0";
pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {