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</pre><pre class="rust"><code><span class="comment">// Copyright 2018 Developers of the Rand project.
//
// Licensed under the Apache License, Version 2.0 &lt;LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0&gt; or the MIT license
// &lt;LICENSE-MIT or https://opensource.org/licenses/MIT&gt;, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
</span><span class="doccomment">//! Implementations that just need to read from a file
</span><span class="kw">use crate</span>::{
util::LazyUsize,
util_libc::{open_readonly, sys_fill_exact},
Error,
};
<span class="kw">use </span>core::{
cell::UnsafeCell,
mem::MaybeUninit,
sync::atomic::{AtomicUsize, Ordering::Relaxed},
};
<span class="comment">// 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, macOS, and QNX Neutrino the devices are identical.
</span><span class="attribute">#[cfg(any(target_os = <span class="string">&quot;solaris&quot;</span>, target_os = <span class="string">&quot;illumos&quot;</span>))]
</span><span class="kw">const </span>FILE_PATH: <span class="kw-2">&amp;</span>str = <span class="string">&quot;/dev/random\0&quot;</span>;
<span class="attribute">#[cfg(any(
target_os = <span class="string">&quot;aix&quot;</span>,
target_os = <span class="string">&quot;android&quot;</span>,
target_os = <span class="string">&quot;linux&quot;</span>,
target_os = <span class="string">&quot;redox&quot;</span>,
target_os = <span class="string">&quot;dragonfly&quot;</span>,
target_os = <span class="string">&quot;haiku&quot;</span>,
target_os = <span class="string">&quot;macos&quot;</span>,
target_os = <span class="string">&quot;nto&quot;</span>,
))]
</span><span class="kw">const </span>FILE_PATH: <span class="kw-2">&amp;</span>str = <span class="string">&quot;/dev/urandom\0&quot;</span>;
<span class="kw">pub fn </span>getrandom_inner(dest: <span class="kw-2">&amp;mut </span>[MaybeUninit&lt;u8&gt;]) -&gt; <span class="prelude-ty">Result</span>&lt;(), Error&gt; {
<span class="kw">let </span>fd = get_rng_fd()<span class="question-mark">?</span>;
sys_fill_exact(dest, |buf| <span class="kw">unsafe </span>{
libc::read(fd, buf.as_mut_ptr() <span class="kw">as </span><span class="kw-2">*mut </span>libc::c_void, buf.len())
})
}
<span class="comment">// Returns the file descriptor for the device file used to retrieve random
// bytes. The file will be opened exactly once. All subsequent calls will
// return the same file descriptor. This file descriptor is never closed.
</span><span class="kw">fn </span>get_rng_fd() -&gt; <span class="prelude-ty">Result</span>&lt;libc::c_int, Error&gt; {
<span class="kw">static </span>FD: AtomicUsize = AtomicUsize::new(LazyUsize::UNINIT);
<span class="kw">fn </span>get_fd() -&gt; <span class="prelude-ty">Option</span>&lt;libc::c_int&gt; {
<span class="kw">match </span>FD.load(Relaxed) {
LazyUsize::UNINIT =&gt; <span class="prelude-val">None</span>,
val =&gt; <span class="prelude-val">Some</span>(val <span class="kw">as </span>libc::c_int),
}
}
<span class="comment">// Use double-checked locking to avoid acquiring the lock if possible.
</span><span class="kw">if let </span><span class="prelude-val">Some</span>(fd) = get_fd() {
<span class="kw">return </span><span class="prelude-val">Ok</span>(fd);
}
<span class="comment">// SAFETY: We use the mutex only in this method, and we always unlock it
// before returning, making sure we don&#39;t violate the pthread_mutex_t API.
</span><span class="kw">static </span>MUTEX: Mutex = Mutex::new();
<span class="kw">unsafe </span>{ MUTEX.lock() };
<span class="kw">let </span>_guard = DropGuard(|| <span class="kw">unsafe </span>{ MUTEX.unlock() });
<span class="kw">if let </span><span class="prelude-val">Some</span>(fd) = get_fd() {
<span class="kw">return </span><span class="prelude-val">Ok</span>(fd);
}
<span class="comment">// On Linux, /dev/urandom might return insecure values.
</span><span class="attribute">#[cfg(any(target_os = <span class="string">&quot;android&quot;</span>, target_os = <span class="string">&quot;linux&quot;</span>))]
</span>wait_until_rng_ready()<span class="question-mark">?</span>;
<span class="kw">let </span>fd = <span class="kw">unsafe </span>{ open_readonly(FILE_PATH)<span class="question-mark">? </span>};
<span class="comment">// The fd always fits in a usize without conflicting with UNINIT.
</span><span class="macro">debug_assert!</span>(fd &gt;= <span class="number">0 </span>&amp;&amp; (fd <span class="kw">as </span>usize) &lt; LazyUsize::UNINIT);
FD.store(fd <span class="kw">as </span>usize, Relaxed);
<span class="prelude-val">Ok</span>(fd)
}
<span class="comment">// Succeeds once /dev/urandom is safe to read from
</span><span class="attribute">#[cfg(any(target_os = <span class="string">&quot;android&quot;</span>, target_os = <span class="string">&quot;linux&quot;</span>))]
</span><span class="kw">fn </span>wait_until_rng_ready() -&gt; <span class="prelude-ty">Result</span>&lt;(), Error&gt; {
<span class="comment">// Poll /dev/random to make sure it is ok to read from /dev/urandom.
</span><span class="kw">let </span>fd = <span class="kw">unsafe </span>{ open_readonly(<span class="string">&quot;/dev/random\0&quot;</span>)<span class="question-mark">? </span>};
<span class="kw">let </span><span class="kw-2">mut </span>pfd = libc::pollfd {
fd,
events: libc::POLLIN,
revents: <span class="number">0</span>,
};
<span class="kw">let </span>_guard = DropGuard(|| <span class="kw">unsafe </span>{
libc::close(fd);
});
<span class="kw">loop </span>{
<span class="comment">// A negative timeout means an infinite timeout.
</span><span class="kw">let </span>res = <span class="kw">unsafe </span>{ libc::poll(<span class="kw-2">&amp;mut </span>pfd, <span class="number">1</span>, -<span class="number">1</span>) };
<span class="kw">if </span>res &gt;= <span class="number">0 </span>{
<span class="macro">debug_assert_eq!</span>(res, <span class="number">1</span>); <span class="comment">// We only used one fd, and cannot timeout.
</span><span class="kw">return </span><span class="prelude-val">Ok</span>(());
}
<span class="kw">let </span>err = <span class="kw">crate</span>::util_libc::last_os_error();
<span class="kw">match </span>err.raw_os_error() {
<span class="prelude-val">Some</span>(libc::EINTR) | <span class="prelude-val">Some</span>(libc::EAGAIN) =&gt; <span class="kw">continue</span>,
<span class="kw">_ </span>=&gt; <span class="kw">return </span><span class="prelude-val">Err</span>(err),
}
}
}
<span class="kw">struct </span>Mutex(UnsafeCell&lt;libc::pthread_mutex_t&gt;);
<span class="kw">impl </span>Mutex {
<span class="kw">const fn </span>new() -&gt; <span class="self">Self </span>{
<span class="self">Self</span>(UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER))
}
<span class="kw">unsafe fn </span>lock(<span class="kw-2">&amp;</span><span class="self">self</span>) {
<span class="kw">let </span>r = libc::pthread_mutex_lock(<span class="self">self</span>.<span class="number">0</span>.get());
<span class="macro">debug_assert_eq!</span>(r, <span class="number">0</span>);
}
<span class="kw">unsafe fn </span>unlock(<span class="kw-2">&amp;</span><span class="self">self</span>) {
<span class="kw">let </span>r = libc::pthread_mutex_unlock(<span class="self">self</span>.<span class="number">0</span>.get());
<span class="macro">debug_assert_eq!</span>(r, <span class="number">0</span>);
}
}
<span class="kw">unsafe impl </span>Sync <span class="kw">for </span>Mutex {}
<span class="kw">struct </span>DropGuard&lt;F: FnMut()&gt;(F);
<span class="kw">impl</span>&lt;F: FnMut()&gt; Drop <span class="kw">for </span>DropGuard&lt;F&gt; {
<span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="self">self</span>.<span class="number">0</span>()
}
}
</code></pre></div>
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