A re-review showed the previous "single import choke point" claim was wrong:
`plugins` is a normal importable package, so core request handlers that do
`from plugins.<name>.models import ...` never passed through the loader and ran
unverified - an attacker who dropped a file into plugins/<name>/ got arbitrary
in-process code execution on an ordinary HTTP request (and a planted .pyc ran
from cache). Gating load_plugin_class covered only plugin.py, one path of many.
Fix: importguard.py installs a sys.meta_path finder (under enforcement) that
intercepts EVERY plugins.<name>.* import, verifies the plugin's signed
provenance once, then verifies each module file against it and execs the exact
bytes it hashed - read once, compiled, exec'd, never a .pyc, never a re-opened
file. This closes the submodule bypass and the planted-bytecode read, and the
read-once exec closes the verify-vs-exec TOCTOU on the import path. The import
system, not one method, is the real choke point.
- init_app installs the guard when PLUGIN_REQUIRE_SIGNED, clears it otherwise.
- load_plugin_class now verifies plugin.py from a single read and execs that
buffer (finding #3 on that file); its submodule imports flow through the guard.
- docs: stamp-bundled must cover every plugin dir present (a disabled plugin's
module can be imported by core); recommend a read-only plugins/ owned by the
deploy user as defense in depth (closes the residual migrate-time race an
attacker with concurrent write could otherwise attempt).
Earlier review's fixes#3 (migrate code paths) and #4 (shelf content binding)
were confirmed sound and are unchanged. 7 import-guard tests (submodule verify,
tamper, unsigned refused, planted .pyc ignored, real import through the guard,
install/uninstall). 1061 pass, naming green.
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