A bug in the SmallVec::insert_many method caused it to allocate a buffer that was smaller than needed. It then wrote past the end of the buffer, causing a buffer overflow and memory corruption on the heap.

This bug was only triggered if the iterator passed to insert_many yielded more items than the lower bound returned from its size_hint method.

The flaw was corrected in smallvec 0.6.14 and 1.6.1, by ensuring that additional space is always reserved for each item inserted. The fix also simplified the implementation of insert_many to use less unsafe code, so it is easier to verify its correctness.

Thank you to Yechan Bae (@Qwaz) and the Rust group at Georgia Tech’s SSLab for finding and reporting this bug.

PyString::from_object took &str arguments and forwarded them directly to the Python C API without checking for terminating nul bytes. This could lead the Python interpreter to read beyond the end of the &str data and potentially leak contents of the out-of-bounds read (by raising a Python exception containing a copy of the data including the overflow).

In PyO3 0.24.1 this function will now allocate a CString to guarantee a terminating nul bytes. PyO3 0.25 will likely offer an alternative API which takes &CStr arguments.