getrandom/
linux_android_with_fallback.rs

1//! Implementation for Linux / Android with `/dev/urandom` fallback
2use crate::{
3    lazy::LazyBool,
4    util_libc::{getrandom_syscall, last_os_error, sys_fill_exact},
5    {use_file, Error},
6};
7use core::mem::MaybeUninit;
8
9pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
10    // getrandom(2) was introduced in Linux 3.17
11    static HAS_GETRANDOM: LazyBool = LazyBool::new();
12    if HAS_GETRANDOM.unsync_init(is_getrandom_available) {
13        sys_fill_exact(dest, getrandom_syscall)
14    } else {
15        use_file::getrandom_inner(dest)
16    }
17}
18
19fn is_getrandom_available() -> bool {
20    if getrandom_syscall(&mut []) < 0 {
21        match last_os_error().raw_os_error() {
22            Some(libc::ENOSYS) => false, // No kernel support
23            // The fallback on EPERM is intentionally not done on Android since this workaround
24            // seems to be needed only for specific Linux-based products that aren't based
25            // on Android. See https://github.com/rust-random/getrandom/issues/229.
26            #[cfg(target_os = "linux")]
27            Some(libc::EPERM) => false, // Blocked by seccomp
28            _ => true,
29        }
30    } else {
31        true
32    }
33}