Use-after-free (?) in overwriteIndexFromFile #882
Description
This is documented in more detail internally at http://jira/SDLC-37809, and I'll try to extract a public test case, but after switching to Node 18, we're seeing what appears to be memory corruption in libgit2, which as best as I can tell is because overwriteIndexFromFile in node/lib/util/git_util.js opens up a NodeGit Index object (newIndex), stores the pointers to the IndexEntry objects it contains, and then allows the Index object to be freed. This mostly manifests as libgit2 complaining the file mode is zero, sometimes as libgit2 complaining a path is invalid, and at least once as a segfault in strcmp.
I suspect this isn't happening in the public repo's CI because we're not triggering the same memory-allocation patterns - the internal repo has about 15K submodules and is also using a pre-commit hook, both of which appear to be necessary.
Modifying the code to intentionally leak newIndex seems to avoid the memory corruption. I'm not actually sure how to properly do this with the exposed nodegit API, since there doesn't appear to be a deep-copy function on IndexEntry.