auto merge of #9108 : blake2-ppc/rust/hazards-on-overflow, r=alexcrichton

Fix uint overflow bugs in std::{at_vec, vec, str}

Closes #8742

Fix issue #8742, which summarized is: unsafe code in vec and str did assume
that a reservation for `X + Y` elements always succeeded, and didn't overflow.

Introduce the method `Vec::reserve_additional(n)` to make it easy to check for
overflow in `Vec::push` and `Vec::push_all`.

In std::str, simplify and remove a lot of the unsafe code and use `push_str`
instead. With improvements to `.push_str` and the new function
`vec::bytes::push_bytes`, it looks like this change has either no or positive
impact on performance.

I believe there are many places still where `v.reserve(A + B)` still can overflow.
This by itself is not an issue unless followed by (unsafe) code that steps aside
boundary checks.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libstd/rt/io/extensions.rs b/src/libstd/rt/io/extensions.rs
index e221f0ee94d..1c48d6e7f1e 100644
--- a/src/libstd/rt/io/extensions.rs
+++ b/src/libstd/rt/io/extensions.rs
@@ -303,7 +303,7 @@ impl<T: Reader> ReaderUtil for T {
             let start_len = buf.len();
             let mut total_read = 0;
 
-            buf.reserve_at_least(start_len + len);
+            buf.reserve_additional(len);
             vec::raw::set_len(buf, start_len + len);
 
             do (|| {