Auto merge of rust-lang#81151 - Mark-Simulacrum:beta-next, r=Mark-Simulacrum

[beta] backports

This backports:

*  Update RLS and Rustfmt rust-lang#81027
*  bump rustfmt to v1.4.32 rust-lang#81093
*  Fix handling of malicious Readers in read_to_end rust-lang#80895
*  Fix broken ./x.py install rust-lang#80514
*  Fix x.py install not working with relative prefix rust-lang#80797
*  [security] Update mdbook rust-lang#80688
*  rustdoc: Render visibilities succinctly rust-lang#80368

r? `@ghost`

Author: bors

Cargo.lock

@@ -1973,9 +1973,9 @@ dependencies = [
 
 [[package]]
 name = "mdbook"
-version = "0.4.3"
+version = "0.4.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "29be448fcafb00c5a8966c4020c2a5ffbbc333e5b96d0bb5ef54b5bd0524d9ff"
+checksum = "21251d3eb9ca5e8ac5b73384ddaa483a9bbc7d7dcd656b1fa8f266634810334a"
 dependencies = [
  "ammonia",
  "anyhow",

library/std/src/io/mod.rs

@@ -367,7 +367,6 @@ where
 {
     let start_len = buf.len();
     let mut g = Guard { len: buf.len(), buf };
-    let ret;
     loop {
         if g.len == g.buf.len() {
             unsafe {
@@ -386,21 +385,20 @@ where
             }
         }
 
-        match r.read(&mut g.buf[g.len..]) {
-            Ok(0) => {
-                ret = Ok(g.len - start_len);
-                break;
+        let buf = &mut g.buf[g.len..];
+        match r.read(buf) {
+            Ok(0) => return Ok(g.len - start_len),
+            Ok(n) => {
+                // We can't allow bogus values from read. If it is too large, the returned vec could have its length
+                // set past its capacity, or if it overflows the vec could be shortened which could create an invalid
+                // string if this is called via read_to_string.
+                assert!(n <= buf.len());
+                g.len += n;
             }
-            Ok(n) => g.len += n,
             Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
-            Err(e) => {
-                ret = Err(e);
-                break;
-            }
+            Err(e) => return Err(e),
         }
     }
-
-    ret
 }
 
 pub(crate) fn default_read_vectored<F>(read: F, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>