1 // Copyright 2018 Developers of the Rand project.
2 //
3 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
4 // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
5 // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
6 // option. This file may not be copied, modified, or distributed
7 // except according to those terms.
8
9 //! Implementations that just need to read from a file
10 use crate::{
11 util::LazyUsize,
12 util_libc::{open_readonly, sys_fill_exact},
13 Error,
14 };
15 use core::{
16 cell::UnsafeCell,
17 sync::atomic::{AtomicUsize, Ordering::Relaxed},
18 };
19
20 #[cfg(any(
21 target_os = "dragonfly",
22 target_os = "emscripten",
23 target_os = "haiku",
24 target_os = "macos",
25 target_os = "solaris",
26 target_os = "illumos"
27 ))]
28 const FILE_PATH: &str = "/dev/random\0";
29 #[cfg(any(target_os = "android", target_os = "linux", target_os = "redox"))]
30 const FILE_PATH: &str = "/dev/urandom\0";
31
getrandom_inner(dest: &mut [u8]) -> Result<(), Error>32 pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
33 let fd = get_rng_fd()?;
34 let read = |buf: &mut [u8]| unsafe { libc::read(fd, buf.as_mut_ptr() as *mut _, buf.len()) };
35
36 if cfg!(target_os = "emscripten") {
37 // `Crypto.getRandomValues` documents `dest` should be at most 65536 bytes.
38 for chunk in dest.chunks_mut(65536) {
39 sys_fill_exact(chunk, read)?;
40 }
41 } else {
42 sys_fill_exact(dest, read)?;
43 }
44 Ok(())
45 }
46
47 // Returns the file descriptor for the device file used to retrieve random
48 // bytes. The file will be opened exactly once. All subsequent calls will
49 // return the same file descriptor. This file descriptor is never closed.
get_rng_fd() -> Result<libc::c_int, Error>50 fn get_rng_fd() -> Result<libc::c_int, Error> {
51 static FD: AtomicUsize = AtomicUsize::new(LazyUsize::UNINIT);
52 fn get_fd() -> Option<libc::c_int> {
53 match FD.load(Relaxed) {
54 LazyUsize::UNINIT => None,
55 val => Some(val as libc::c_int),
56 }
57 }
58
59 // Use double-checked locking to avoid acquiring the lock if possible.
60 if let Some(fd) = get_fd() {
61 return Ok(fd);
62 }
63
64 // SAFETY: We use the mutex only in this method, and we always unlock it
65 // before returning, making sure we don't violate the pthread_mutex_t API.
66 static MUTEX: Mutex = Mutex::new();
67 unsafe { MUTEX.lock() };
68 let _guard = DropGuard(|| unsafe { MUTEX.unlock() });
69
70 if let Some(fd) = get_fd() {
71 return Ok(fd);
72 }
73
74 // On Linux, /dev/urandom might return insecure values.
75 #[cfg(any(target_os = "android", target_os = "linux"))]
76 wait_until_rng_ready()?;
77
78 let fd = unsafe { open_readonly(FILE_PATH)? };
79 // The fd always fits in a usize without conflicting with UNINIT.
80 debug_assert!(fd >= 0 && (fd as usize) < LazyUsize::UNINIT);
81 FD.store(fd as usize, Relaxed);
82
83 Ok(fd)
84 }
85
86 // Succeeds once /dev/urandom is safe to read from
87 #[cfg(any(target_os = "android", target_os = "linux"))]
wait_until_rng_ready() -> Result<(), Error>88 fn wait_until_rng_ready() -> Result<(), Error> {
89 // Poll /dev/random to make sure it is ok to read from /dev/urandom.
90 let fd = unsafe { open_readonly("/dev/random\0")? };
91 let mut pfd = libc::pollfd {
92 fd,
93 events: libc::POLLIN,
94 revents: 0,
95 };
96 let _guard = DropGuard(|| unsafe {
97 libc::close(fd);
98 });
99
100 loop {
101 // A negative timeout means an infinite timeout.
102 let res = unsafe { libc::poll(&mut pfd, 1, -1) };
103 if res >= 0 {
104 debug_assert_eq!(res, 1); // We only used one fd, and cannot timeout.
105 return Ok(());
106 }
107 let err = crate::util_libc::last_os_error();
108 match err.raw_os_error() {
109 Some(libc::EINTR) | Some(libc::EAGAIN) => continue,
110 _ => return Err(err),
111 }
112 }
113 }
114
115 struct Mutex(UnsafeCell<libc::pthread_mutex_t>);
116
117 impl Mutex {
new() -> Self118 const fn new() -> Self {
119 Self(UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER))
120 }
lock(&self)121 unsafe fn lock(&self) {
122 let r = libc::pthread_mutex_lock(self.0.get());
123 debug_assert_eq!(r, 0);
124 }
unlock(&self)125 unsafe fn unlock(&self) {
126 let r = libc::pthread_mutex_unlock(self.0.get());
127 debug_assert_eq!(r, 0);
128 }
129 }
130
131 unsafe impl Sync for Mutex {}
132
133 struct DropGuard<F: FnMut()>(F);
134
135 impl<F: FnMut()> Drop for DropGuard<F> {
drop(&mut self)136 fn drop(&mut self) {
137 self.0()
138 }
139 }
140