73 lines
2.8 KiB
Markdown
73 lines
2.8 KiB
Markdown
# libgit2 — CWE-407 Disclosure Brief
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**2026-03-27 · Patch available — awaiting upstream merge**
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## Finding
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One O(n²) defect in libgit2's filesystem reference backend. `ref_available()` performs an O(R) packed-ref list scan per path segment check — called at 17 sites — causing O(R²) total overhead for repositories with many references. Patch ready for upstream review.
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## The Defects
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**libgit2-0001 (PATCHED — HIGH):** `src/libgit2/refs.c`
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```c
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/* git_refdb_backend_fs.ref_available() — per segment per path check: */
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/* Called at 17 sites */
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static int ref_available(git_refdb_backend *_backend,
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const char *refname, ...)
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{
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/* O(R) packed-ref list scan per segment */
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git_sortedcache_rlock(backend->refcache);
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size_t i;
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for (i = 0; i < git_sortedcache_entrycount(backend->refcache); i++) {
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struct packref *ref = git_sortedcache_entry(backend->refcache, i);
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if (is_prefix_of(ref->name, refname)) { ... }
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}
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/* O(R²) total across 17 call sites */
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}
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```
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O(R) packed-ref scan per path segment check, at 17 call sites. **O(R²) total**. **Measured ratio: 17 sites.**
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## Complexity Proof
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For R packed references:
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- Per `ref_available()` call: O(R) scan
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- 17 call sites per ref operation: O(17×R) per operation
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- R operations: O(R²) total
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- Fixed: binary search on sorted refs → O(R × log R)
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- **17 call sites measured.**
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## Impact
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All libgit2 users and all software built on libgit2: GitHub's Rugged (Ruby), pygit2 (Python), git2go (Go), NodeGit, libgit2sharp (.NET), and Git GUI clients. Repositories with many references (many branches, many tags — common in large monorepos and CI/CD systems) hit O(R²) during reference creation, renaming, and deletion. libgit2 is the foundation of most non-C Git tooling.
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## The Fix
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Use binary search on the sorted reference cache instead of linear scan:
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```c
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/* Before */
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for (i = 0; i < git_sortedcache_entrycount(backend->refcache); i++) {
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struct packref *ref = git_sortedcache_entry(backend->refcache, i);
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if (is_prefix_of(ref->name, refname)) { ... }
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}
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/* After */
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/* CWE-407 fix: binary search on sorted refcache for O(log R) per check. */
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size_t pos;
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int error = git_sortedcache_lookup_raw(backend->refcache, &pos, refname);
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/* Binary search gives insertion point; check neighbors for prefix overlap */
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```
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## Patch
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`defects/libgit2/patch/libgit2-0001-refs-binary-search.patch`
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## What We Ask
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1. Confirm receipt and assign a GitHub Security Advisory or issue reference.
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2. Validate the patch against your reference backend test suite.
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3. Assess CVE eligibility — affects all 17 ref_available call sites in large repositories.
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4. Coordinate a disclosure date — we are targeting 90 days from first contact.
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Contact: see cover email. This brief is confidential until coordinated disclosure.
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