Remove libstd for opening/reading files

Author: josephlr

src/use_file.rs

@@ -7,18 +7,13 @@
 // except according to those terms.
 
 //! Implementations that just need to read from a file
-extern crate std;
-
-use crate::util_libc::{last_os_error, LazyFd};
+use crate::util_libc::{fill_exact, last_os_error, open_readonly, LazyFd};
 use crate::Error;
-use core::mem::ManuallyDrop;
-use std::os::unix::io::{FromRawFd, IntoRawFd, RawFd};
-use std::{fs::File, io::Read};
 
 #[cfg(target_os = "redox")]
-const FILE_PATH: &str = "rand:";
+const FILE_PATH: &str = "rand:\0";
 #[cfg(any(target_os = "android", target_os = "linux", target_os = "netbsd"))]
-const FILE_PATH: &str = "/dev/urandom";
+const FILE_PATH: &str = "/dev/urandom\0";
 #[cfg(any(
     target_os = "dragonfly",
     target_os = "emscripten",
@@ -27,32 +22,50 @@ const FILE_PATH: &str = "/dev/urandom";
     target_os = "solaris",
     target_os = "illumos"
 ))]
-const FILE_PATH: &str = "/dev/random";
+const FILE_PATH: &str = "/dev/random\0";
 
 pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
     static FD: LazyFd = LazyFd::new();
     let fd = FD.init(init_file).ok_or(last_os_error())?;
-    let file = ManuallyDrop::new(unsafe { File::from_raw_fd(fd) });
-    let mut file_ref: &File = &file;
+    let read = |buf: &mut [u8]| unsafe { libc::read(fd, buf.as_mut_ptr() as *mut _, buf.len()) };
 
     if cfg!(target_os = "emscripten") {
         // `Crypto.getRandomValues` documents `dest` should be at most 65536 bytes.
         for chunk in dest.chunks_mut(65536) {
-            file_ref.read_exact(chunk)?;
+            fill_exact(chunk, read)?;
         }
     } else {
-        file_ref.read_exact(dest)?;
+        fill_exact(dest, read)?;
     }
     Ok(())
 }
 
-fn init_file() -> Option<RawFd> {
-    if FILE_PATH == "/dev/urandom" {
-        // read one byte from "/dev/random" to ensure that OS RNG has initialized
-        File::open("/dev/random")
-            .ok()?
-            .read_exact(&mut [0u8; 1])
-            .ok()?;
+fn init_file() -> Option<libc::c_int> {
+    if FILE_PATH == "/dev/urandom\0" {
+        // Poll /dev/random to make sure it is ok to read from /dev/urandom.
+        let mut pfd = libc::pollfd {
+            fd: unsafe { open_readonly("/dev/random\0")? },
+            events: libc::POLLIN,
+            revents: 0,
+        };
+
+        let mut res = -1;
+        while res <= 0 {
+            // A negative timeout means an infinite timeout.
+            res = unsafe { libc::poll(&mut pfd, 1, -1) };
+            if res < 0 {
+                match last_os_error().raw_os_error() {
+                    Some(libc::EINTR) | Some(libc::EAGAIN) => {}
+                    _ => break,
+                }
+            }
+        }
+
+        unsafe { libc::close(pfd.fd) };
+        if res != 1 {
+            // We either hard failed, or poll() returned the wrong pfd.
+            return None;
+        }
     }
-    Some(File::open(FILE_PATH).ok()?.into_raw_fd())
+    unsafe { open_readonly(FILE_PATH) }
 }

src/util_libc.rs

@@ -115,3 +115,22 @@ impl LazyFd {
         }
     }
 }
+
+cfg_if! {
+    if #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "l4re"))] {
+        use libc::open64 as open;
+    } else {
+        use libc::open;
+    }
+}
+
+// SAFETY: path must be null terminated, FD must be manually closed.
+pub unsafe fn open_readonly(path: &str) -> Option<libc::c_int> {
+    // We don't care about kernels too old to support O_CLOEXEC.
+    let fd = open(path.as_ptr() as *mut _, libc::O_RDONLY | libc::O_CLOEXEC);
+    if fd < 0 {
+        None
+    } else {
+        Some(fd)
+    }
+}