tree 6a385ca356225aac577060f54abd7c45e52658ad
parent 417a7dee1c4653bd3a4753710a84c8fd356ba7d9
author Thomas Anderson <thomasanderson@google.com> 1551906608 +0000
committer Thomas Anderson <thomasanderson@google.com> 1551906608 +0000

[libc++] Fix use-after-free when building with _LIBCPP_DEBUG=1

The issue is the following code:

    __cn1->__add(*__ip);
    (*__ip)->__c_ = __cn1;

`__ip` points into the array of iterators for container `__cn2`.  This code adds
the iterator to the array of iterators for `__cn1`, and updates the iterator to
point to the new container.

This code works fine, except when `__cn1` and `__cn2` are the same container.
`__cn1->__add()` might need to grow the array of iterators, and when it does,
`__ip` becomes invalid, so the second line becomes a use-after-free error.

Simply swapping the order of the above two lines is not sufficient, because of
the memmove() below.  The easiest and most performant solution is just to skip
touching any iterators if the containers are the same.

Differential Revision: https://reviews.llvm.org/D58926


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@355550 91177308-0d34-0410-b5e6-96231b3b80d8