1 files changed, 234 insertions, 0 deletions
diff --git a/vendor/getrandom/src/backends/use_file.rs b/vendor/getrandom/src/backends/use_file.rs
new file mode 100644
index 00000000..7b48d433
--- /dev/null
+++ b/vendor/getrandom/src/backends/use_file.rs
@@ -0,0 +1,234 @@
+//! Implementations that just need to read from a file
+use crate::Error;
+use core::{
+    ffi::c_void,
+    mem::MaybeUninit,
+    sync::atomic::{AtomicI32, Ordering},
+};
+
+#[cfg(not(any(target_os = "android", target_os = "linux")))]
+pub use crate::util::{inner_u32, inner_u64};
+
+#[path = "../util_libc.rs"]
+pub(super) mod util_libc;
+
+/// For all platforms, we use `/dev/urandom` rather than `/dev/random`.
+/// For more information see the linked man pages in lib.rs.
+///   - On Linux, "/dev/urandom is preferred and sufficient in all use cases".
+///   - On Redox, only /dev/urandom is provided.
+///   - On AIX, /dev/urandom will "provide cryptographically secure output".
+///   - On Haiku and QNX Neutrino they are identical.
+const FILE_PATH: &[u8] = b"/dev/urandom\0";
+
+// File descriptor is a "nonnegative integer", so we can safely use negative sentinel values.
+const FD_UNINIT: libc::c_int = -1;
+const FD_ONGOING_INIT: libc::c_int = -2;
+
+// In theory `libc::c_int` could be something other than `i32`, but for the
+// targets we currently support that use `use_file`, it is always `i32`.
+// If/when we add support for a target where that isn't the case, we may
+// need to use a different atomic type or make other accomodations. The
+// compiler will let us know if/when that is the case, because the
+// `FD.store(fd)` would fail to compile.
+//
+// The opening of the file, by libc/libstd/etc. may write some unknown
+// state into in-process memory. (Such state may include some sanitizer
+// bookkeeping, or we might be operating in a unikernal-like environment
+// where all the "kernel" file descriptor bookkeeping is done in our
+// process.) `get_fd_locked` stores into FD using `Ordering::Release` to
+// ensure any such state is synchronized. `get_fd` loads from `FD` with
+// `Ordering::Acquire` to synchronize with it.
+static FD: AtomicI32 = AtomicI32::new(FD_UNINIT);
+
+#[inline]
+pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
+    let mut fd = FD.load(Ordering::Acquire);
+    if fd == FD_UNINIT || fd == FD_ONGOING_INIT {
+        fd = open_or_wait()?;
+    }
+    util_libc::sys_fill_exact(dest, |buf| unsafe {
+        libc::read(fd, buf.as_mut_ptr().cast::<c_void>(), buf.len())
+    })
+}
+
+/// Open a file in read-only mode.
+///
+/// # Panics
+/// If `path` does not contain any zeros.
+// TODO: Move `path` to `CStr` and use `CStr::from_bytes_until_nul` (MSRV 1.69)
+// or C-string literals (MSRV 1.77) for statics
+fn open_readonly(path: &[u8]) -> Result<libc::c_int, Error> {
+    assert!(path.contains(&0));
+    loop {
+        let fd = unsafe {
+            libc::open(
+                path.as_ptr().cast::<libc::c_char>(),
+                libc::O_RDONLY | libc::O_CLOEXEC,
+            )
+        };
+        if fd >= 0 {
+            return Ok(fd);
+        }
+        let err = util_libc::last_os_error();
+        // We should try again if open() was interrupted.
+        if err.raw_os_error() != Some(libc::EINTR) {
+            return Err(err);
+        }
+    }
+}
+
+#[cold]
+#[inline(never)]
+fn open_or_wait() -> Result<libc::c_int, Error> {
+    loop {
+        match FD.load(Ordering::Acquire) {
+            FD_UNINIT => {
+                let res = FD.compare_exchange_weak(
+                    FD_UNINIT,
+                    FD_ONGOING_INIT,
+                    Ordering::AcqRel,
+                    Ordering::Relaxed,
+                );
+                if res.is_ok() {
+                    break;
+                }
+            }
+            FD_ONGOING_INIT => sync::wait(),
+            fd => return Ok(fd),
+        }
+    }
+
+    let res = open_fd();
+    let val = match res {
+        Ok(fd) => fd,
+        Err(_) => FD_UNINIT,
+    };
+    FD.store(val, Ordering::Release);
+
+    // On non-Linux targets `wait` is just 1 ms sleep,
+    // so we don't need any explicit wake up in addition
+    // to updating value of `FD`.
+    #[cfg(any(target_os = "android", target_os = "linux"))]
+    sync::wake();
+
+    res
+}
+
+fn open_fd() -> Result<libc::c_int, Error> {
+    #[cfg(any(target_os = "android", target_os = "linux"))]
+    sync::wait_until_rng_ready()?;
+    let fd = open_readonly(FILE_PATH)?;
+    debug_assert!(fd >= 0);
+    Ok(fd)
+}
+
+#[cfg(not(any(target_os = "android", target_os = "linux")))]
+mod sync {
+    /// Sleep 1 ms before checking `FD` again.
+    ///
+    /// On non-Linux targets the critical section only opens file,
+    /// which should not block, so in the unlikely contended case,
+    /// we can sleep-wait for the opening operation to finish.
+    pub(super) fn wait() {
+        let rqtp = libc::timespec {
+            tv_sec: 0,
+            tv_nsec: 1_000_000,
+        };
+        let mut rmtp = libc::timespec {
+            tv_sec: 0,
+            tv_nsec: 0,
+        };
+        // We do not care if sleep gets interrupted, so the return value is ignored
+        unsafe {
+            libc::nanosleep(&rqtp, &mut rmtp);
+        }
+    }
+}
+
+#[cfg(any(target_os = "android", target_os = "linux"))]
+mod sync {
+    use super::{open_readonly, util_libc::last_os_error, Error, FD, FD_ONGOING_INIT};
+
+    /// Wait for atomic `FD` to change value from `FD_ONGOING_INIT` to something else.
+    ///
+    /// Futex syscall with `FUTEX_WAIT` op puts the current thread to sleep
+    /// until futex syscall with `FUTEX_WAKE` op gets executed for `FD`.
+    ///
+    /// For more information read: https://www.man7.org/linux/man-pages/man2/futex.2.html
+    pub(super) fn wait() {
+        let op = libc::FUTEX_WAIT | libc::FUTEX_PRIVATE_FLAG;
+        let timeout_ptr = core::ptr::null::<libc::timespec>();
+        let ret = unsafe { libc::syscall(libc::SYS_futex, &FD, op, FD_ONGOING_INIT, timeout_ptr) };
+        // FUTEX_WAIT should return either 0 or EAGAIN error
+        debug_assert!({
+            match ret {
+                0 => true,
+                -1 => last_os_error().raw_os_error() == Some(libc::EAGAIN),
+                _ => false,
+            }
+        });
+    }
+
+    /// Wake up all threads which wait for value of atomic `FD` to change.
+    pub(super) fn wake() {
+        let op = libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG;
+        let ret = unsafe { libc::syscall(libc::SYS_futex, &FD, op, libc::INT_MAX) };
+        debug_assert!(ret >= 0);
+    }
+
+    // Polls /dev/random to make sure it is ok to read from /dev/urandom.
+    //
+    // Polling avoids draining the estimated entropy from /dev/random;
+    // short-lived processes reading even a single byte from /dev/random could
+    // be problematic if they are being executed faster than entropy is being
+    // collected.
+    //
+    // OTOH, reading a byte instead of polling is more compatible with
+    // sandboxes that disallow `poll()` but which allow reading /dev/random,
+    // e.g. sandboxes that assume that `poll()` is for network I/O. This way,
+    // fewer applications will have to insert pre-sandbox-initialization logic.
+    // Often (blocking) file I/O is not allowed in such early phases of an
+    // application for performance and/or security reasons.
+    //
+    // It is hard to write a sandbox policy to support `libc::poll()` because
+    // it may invoke the `poll`, `ppoll`, `ppoll_time64` (since Linux 5.1, with
+    // newer versions of glibc), and/or (rarely, and probably only on ancient
+    // systems) `select`. depending on the libc implementation (e.g. glibc vs
+    // musl), libc version, potentially the kernel version at runtime, and/or
+    // the target architecture.
+    //
+    // BoringSSL and libstd don't try to protect against insecure output from
+    // `/dev/urandom'; they don't open `/dev/random` at all.
+    //
+    // OpenSSL uses `libc::select()` unless the `dev/random` file descriptor
+    // is too large; if it is too large then it does what we do here.
+    //
+    // libsodium uses `libc::poll` similarly to this.
+    pub(super) fn wait_until_rng_ready() -> Result<(), Error> {
+        let fd = open_readonly(b"/dev/random\0")?;
+        let mut pfd = libc::pollfd {
+            fd,
+            events: libc::POLLIN,
+            revents: 0,
+        };
+
+        let res = loop {
+            // A negative timeout means an infinite timeout.
+            let res = unsafe { libc::poll(&mut pfd, 1, -1) };
+            if res >= 0 {
+                // We only used one fd, and cannot timeout.
+                debug_assert_eq!(res, 1);
+                break Ok(());
+            }
+            let err = last_os_error();
+            // Assuming that `poll` is called correctly,
+            // on Linux it can return only EINTR and ENOMEM errors.
+            match err.raw_os_error() {
+                Some(libc::EINTR) => continue,
+                _ => break Err(err),
+            }
+        };
+        unsafe { libc::close(fd) };
+        res
+    }
+}