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(target_os = "redox")]
21 const FILE_PATH: &str = "rand:\0";
22 #[cfg(any(
23 target_os = "dragonfly",
24 target_os = "emscripten",
25 target_os = "haiku",
26 target_os = "macos",
27 target_os = "solaris",
28 target_os = "illumos"
29 ))]
30 const FILE_PATH: &str = "/dev/random\0";
31 #[cfg(any(target_os = "android", target_os = "linux"))]
32 const FILE_PATH: &str = "/dev/urandom\0";
33
getrandom_inner(dest: &mut [u8]) -> Result<(), Error>34 pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
35 let fd = get_rng_fd()?;
36 let read = |buf: &mut [u8]| unsafe { libc::read(fd, buf.as_mut_ptr() as *mut _, buf.len()) };
37
38 if cfg!(target_os = "emscripten") {
39 // `Crypto.getRandomValues` documents `dest` should be at most 65536 bytes.
40 for chunk in dest.chunks_mut(65536) {
41 sys_fill_exact(chunk, read)?;
42 }
43 } else {
44 sys_fill_exact(dest, read)?;
45 }
46 Ok(())
47 }
48
49 // Returns the file descriptor for the device file used to retrieve random
50 // bytes. The file will be opened exactly once. All successful calls will
51 // return the same file descriptor. This file descriptor is never closed.
get_rng_fd() -> Result<libc::c_int, Error>52 fn get_rng_fd() -> Result<libc::c_int, Error> {
53 static FD: AtomicUsize = AtomicUsize::new(LazyUsize::UNINIT);
54 fn get_fd() -> Option<libc::c_int> {
55 match FD.load(Relaxed) {
56 LazyUsize::UNINIT => None,
57 val => Some(val as libc::c_int),
58 }
59 }
60
61 // Use double-checked locking to avoid acquiring the lock if possible.
62 if let Some(fd) = get_fd() {
63 return Ok(fd);
64 }
65
66 // SAFETY: We use the mutex only in this method, and we always unlock it
67 // before returning, making sure we don't violate the pthread_mutex_t API.
68 static MUTEX: Mutex = Mutex::new();
69 unsafe { MUTEX.lock() };
70 let _guard = DropGuard(|| unsafe { MUTEX.unlock() });
71
72 if let Some(fd) = get_fd() {
73 return Ok(fd);
74 }
75
76 // On Linux, /dev/urandom might return insecure values.
77 #[cfg(any(target_os = "android", target_os = "linux"))]
78 wait_until_rng_ready()?;
79
80 let fd = unsafe { open_readonly(FILE_PATH)? };
81 // The fd always fits in a usize without conflicting with UNINIT.
82 debug_assert!(fd >= 0 && (fd as usize) < LazyUsize::UNINIT);
83 FD.store(fd as usize, Relaxed);
84
85 Ok(fd)
86 }
87
88 // Succeeds once /dev/urandom is safe to read from
89 #[cfg(any(target_os = "android", target_os = "linux"))]
wait_until_rng_ready() -> Result<(), Error>90 fn wait_until_rng_ready() -> Result<(), Error> {
91 // Poll /dev/random to make sure it is ok to read from /dev/urandom.
92 let fd = unsafe { open_readonly("/dev/random\0")? };
93 let mut pfd = libc::pollfd {
94 fd,
95 events: libc::POLLIN,
96 revents: 0,
97 };
98 let _guard = DropGuard(|| unsafe {
99 libc::close(fd);
100 });
101
102 loop {
103 // A negative timeout means an infinite timeout.
104 let res = unsafe { libc::poll(&mut pfd, 1, -1) };
105 if res >= 0 {
106 debug_assert_eq!(res, 1); // We only used one fd, and cannot timeout.
107 return Ok(());
108 }
109 let err = crate::util_libc::last_os_error();
110 match err.raw_os_error() {
111 Some(libc::EINTR) | Some(libc::EAGAIN) => continue,
112 _ => return Err(err),
113 }
114 }
115 }
116
117 struct Mutex(UnsafeCell<libc::pthread_mutex_t>);
118
119 impl Mutex {
new() -> Self120 const fn new() -> Self {
121 Self(UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER))
122 }
lock(&self)123 unsafe fn lock(&self) {
124 let r = libc::pthread_mutex_lock(self.0.get());
125 debug_assert_eq!(r, 0);
126 }
unlock(&self)127 unsafe fn unlock(&self) {
128 let r = libc::pthread_mutex_unlock(self.0.get());
129 debug_assert_eq!(r, 0);
130 }
131 }
132
133 unsafe impl Sync for Mutex {}
134
135 struct DropGuard<F: FnMut()>(F);
136
137 impl<F: FnMut()> Drop for DropGuard<F> {
drop(&mut self)138 fn drop(&mut self) {
139 self.0()
140 }
141 }
142