io: fix unsound pin projection in read_buf and write_buf (#2612)

tokio/src/io/util/async_read_ext.rs

@@ -221,7 +221,7 @@ cfg_io_util! {
         /// ```
         fn read_buf<'a, B>(&'a mut self, buf: &'a mut B) -> ReadBuf<'a, Self, B>
         where
-            Self: Sized,
+            Self: Sized + Unpin,
             B: BufMut,
         {
             read_buf(self, buf)

tokio/src/io/util/async_write_ext.rs

@@ -180,7 +180,7 @@ cfg_io_util! {
         /// ```
         fn write_buf<'a, B>(&'a mut self, src: &'a mut B) -> WriteBuf<'a, Self, B>
         where
-            Self: Sized,
+            Self: Sized + Unpin,
             B: Buf,
         {
             write_buf(self, src)

tokio/src/io/util/read_buf.rs

@@ -8,7 +8,7 @@ use std::task::{Context, Poll};
 
 pub(crate) fn read_buf<'a, R, B>(reader: &'a mut R, buf: &'a mut B) -> ReadBuf<'a, R, B>
 where
-    R: AsyncRead,
+    R: AsyncRead + Unpin,
     B: BufMut,
 {
     ReadBuf { reader, buf }
@@ -26,16 +26,13 @@ cfg_io_util! {
 
 impl<R, B> Future for ReadBuf<'_, R, B>
 where
-    R: AsyncRead,
+    R: AsyncRead + Unpin,
     B: BufMut,
 {
     type Output = io::Result<usize>;
 
-    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
-        // safety: no data is moved from self
+        let me = &mut *self;
-        unsafe {
+        Pin::new(&mut *me.reader).poll_read_buf(cx, me.buf)
-            let me = self.get_unchecked_mut();
-            Pin::new_unchecked(&mut *me.reader).poll_read_buf(cx, &mut me.buf)
-        }
     }
 }

tokio/src/io/util/write_buf.rs

@@ -20,7 +20,7 @@ cfg_io_util! {
 /// asynchronous manner, returning a future.
 pub(crate) fn write_buf<'a, W, B>(writer: &'a mut W, buf: &'a mut B) -> WriteBuf<'a, W, B>
 where
-    W: AsyncWrite,
+    W: AsyncWrite + Unpin,
     B: Buf,
 {
     WriteBuf { writer, buf }
@@ -28,16 +28,13 @@ where
 
 impl<W, B> Future for WriteBuf<'_, W, B>
 where
-    W: AsyncWrite,
+    W: AsyncWrite + Unpin,
     B: Buf,
 {
     type Output = io::Result<usize>;
 
-    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
-        // safety: no data is moved from self
+        let me = &mut *self;
-        unsafe {
+        Pin::new(&mut *me.writer).poll_write_buf(cx, me.buf)
-            let me = self.get_unchecked_mut();
-            Pin::new_unchecked(&mut *me.writer).poll_write_buf(cx, &mut me.buf)
-        }
     }
 }