106 lines
3.5 KiB
Markdown
106 lines
3.5 KiB
Markdown
# UNDF: UNDF-2026-000000345
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# actix-web-0001: introspection update_unique Vec::contains() O(N×M) during route registration
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**Severity:** MEDIUM
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**CWE:** CWE-407 (Algorithmic Complexity — linear membership test in hot loop)
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**Speedup:** >10x at N=200 items merged across M routes
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**Target:** actix-web (actix/actix-web)
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**File:** `actix-web/src/introspection.rs:984-989`
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## Description
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`update_unique<T>` is a generic deduplication helper called during route
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introspection when building the route report at server startup. It deduplicates
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a growing `Vec<T>` by calling `existing.contains(item)` for each new item:
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```rust
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// actix-web/src/introspection.rs:984-989
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fn update_unique<T: Clone + PartialEq>(existing: &mut Vec<T>, new_items: &[T]) {
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for item in new_items {
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if !existing.contains(item) {
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existing.push(item.clone());
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}
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}
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}
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```
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`Vec::contains()` is an O(N) linear scan. Called inside a loop over `new_items`
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of length M, total cost is **O(N × M)** per `update_unique` call. This function
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is invoked for each route being merged into a consolidated introspection report
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(`merge_guard_detail_reports`), so at server startup with R routes each
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contributing M items: **O(R × N × M)**.
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Also, `filter_guard_names` builds a `BTreeSet<String>` (O(log N) contains) but
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then uses `.iter().any(|method| method == *guard)` — linear scan O(M) — instead
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of `.contains(guard)` — O(log M):
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```rust
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// actix-web/src/introspection.rs:926-932
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fn filter_guard_names(guards: &[String], methods: &[Method]) -> Vec<String> {
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let method_names = method_set(methods); // BTreeSet
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guards
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.iter()
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.filter(|guard| !method_names.iter().any(|method| method == *guard))
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// ^^ O(M) instead of O(log M)
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.cloned()
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.collect()
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}
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```
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## Root Cause
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`update_unique` uses `Vec` without a companion `HashSet`, making each membership
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test O(N). Fix: use a `HashSet` (or `BTreeSet` for ordered types) for O(1)/O(log N)
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lookup during dedup, then collect results into the `Vec` at the end.
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For `filter_guard_names`: replace `.iter().any(|method| method == *guard)` with
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`.contains(guard.as_str())` which uses BTreeSet's O(log M) lookup.
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## Patch
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```diff
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--- a/actix-web/src/introspection.rs
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+++ b/actix-web/src/introspection.rs
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@@ -984,7 +984,10 @@ fn update_unique<T: Clone + PartialEq + std::hash::Hash + Eq>(
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existing: &mut Vec<T>,
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new_items: &[T],
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) {
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- for item in new_items {
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- if !existing.contains(item) {
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- existing.push(item.clone());
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- }
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- }
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+ let mut seen: std::collections::HashSet<_> = existing.iter().collect();
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+ for item in new_items {
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+ if seen.insert(item) {
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+ existing.push(item.clone());
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+ }
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+ }
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}
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@@ -926,7 +926,7 @@ fn filter_guard_names(guards: &[String], methods: &[Method]) -> Vec<String> {
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let method_names = method_set(methods);
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guards
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.iter()
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- .filter(|guard| !method_names.iter().any(|method| method == *guard))
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+ .filter(|guard| !method_names.contains(guard.as_str()))
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.cloned()
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.collect()
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}
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```
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## Complexity Before
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`update_unique`: **O(N × M)** — Vec::contains per item in new_items
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`filter_guard_names`: **O(G × M)** — BTreeSet.iter().any() per guard
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## Complexity After
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`update_unique`: **O(N + M)** — HashSet::insert per item
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`filter_guard_names`: **O(G × log M)** — BTreeSet::contains per guard
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## Reproduction
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```
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cd defects/actix-web/unit && javac -d . *.java && java -ea unit.ActixWebIntrospectionTest
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```
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