https://bugs.openldap.org/show_bug.cgi?id=10340

Issue ID: 10340 Summary: Potential Buffer Overflow in mdb_rebalance Product: OpenLDAP Version: unspecified Hardware: All OS: All Status: UNCONFIRMED Keywords: needs_review Severity: normal Priority: --- Component: libraries Assignee: bugs@openldap.org Reporter: alexguo1023@gmail.com Target Milestone: ---

Created attachment 1067 --> https://bugs.openldap.org/attachment.cgi?id=1067&action=edit Add an early return when `mc->mc_top == 0`

In `mdb_rebalance`, we do:

```c int ptop = mc->mc_top - 1; node = mc->mc_pg[ptop]; ```

However, `mc->mc_top` defaults to 0 in many contexts, so `ptop` can become `-1`. Indexing `mc->mc_pg[-1]` causes invalid memory access. Elsewhere this is handled by checking `mc->mc_top > 0` before decrementing.

To fix this, we add an early return when `mc->mc_top == 0`. A root page (or one without a parent) doesn’t need rebalancing, so this guard prevents `ptop` from ever being negative and eliminates the out-of-bounds access.