From e83666f45e3d93439775daefda7800b2ab193d30 Mon Sep 17 00:00:00 2001
From: Giacomo Stevanato <giaco.stevanato@gmail.com>
Date: Wed, 28 Oct 2020 18:52:45 +0100
Subject: [PATCH] Prevent String::retain from creating non-utf8 strings when
 abusing panic

---
 library/alloc/src/string.rs | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index 72ed036637d..ce216e5336e 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -1235,6 +1235,10 @@ impl String {
         let mut del_bytes = 0;
         let mut idx = 0;
 
+        unsafe {
+            self.vec.set_len(0);
+        }
+
         while idx < len {
             let ch = unsafe { self.get_unchecked(idx..len).chars().next().unwrap() };
             let ch_len = ch.len_utf8();
@@ -1255,10 +1259,8 @@ impl String {
             idx += ch_len;
         }
 
-        if del_bytes > 0 {
-            unsafe {
-                self.vec.set_len(len - del_bytes);
-            }
+        unsafe {
+            self.vec.set_len(len - del_bytes);
         }
     }