linux: add complexity gate headers to all 8 patches; fix 0003/0007/0008 code issues
- All 8 patches now carry required # CWE-407 / # Defect / # Fix / # Complexity gate header blocks per patch file format spec - linux-0001 (headerdep.pl): header only — code was correct - linux-0002 (auditsc.c): header + explicit break to prevent ctx->names_list fall-through - linux-0003 (dev.c): rewrote fix — skip altname loop when format has no percent-d placeholder; removes duplicate bounds check from prior draft - linux-0004 (neighbour.c): header + cleaned up ifdef guards; xarray with fallback - linux-0005 (component.c): header + existing hash fast-path retained - linux-0006 (btf.c): header + fixed cache hit path — no longer re-runs btf_find_by_name_kind on hit; uses stored btf_id directly - linux-0007 (pktgen.c): rewrote fix — replaced xa_for_each (O(N)) with dual DECLARE_HASHTABLE: dev_ht (by dev*) and name_ht (by jhash(ifname)) - linux-0008 (taskstats.c): fixed mixed list_for_each_entry/hash_for_each_possible syntax; clean replacement of duplicate-pid list scan with hash_for_each_possible - Combined patch: linux-0001..0008-hashstruct.patch (8 defects, was missing 0004) - outreach/linux.md: updated to 8 defects, corrected numbering (0001=headerdep, 0002=auditsc, 0003=dev, 0004=neighbour, 0005-0008 as before)
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10 changed files with 1273 additions and 254 deletions
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@ -1,4 +1,24 @@
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# UNDF: UNDF-2026-000000149
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# CWE-407: Algorithmic Complexity — O(F×M) → O(F) in kernel/bpf/btf.c bpf_find_btf_id()
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#
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# Defect: bpf_find_btf_id() calls idr_for_each_entry() over btf_idr — O(M) where M is
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# the number of loaded kernel modules — for every kptr field encountered during BPF map
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# creation. A struct with F kptr fields costs O(F × M) per map-create syscall. The
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# kernel source comment explicitly acknowledges: "linear search could be slow".
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# In a loaded Kubernetes node (200+ modules): each map-create with 10 kptr fields = 2000
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# BTF iterations.
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#
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# Fix: maintain a secondary hash table btf_name_ht mapping (FNV-1a(name) ^ kind) to btf_id.
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# Built lazily on first miss; entries evicted on module unload (btf_free_id hook).
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# Lookup drops from O(M) to O(1) amortised on cache hit. Slow idr path retained on miss.
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#
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# Complexity gate (conceptual — kernel module load/unload controls M):
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# F=10 kptr fields, M=200 modules:
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# slow: 10 × 200 = 2000 idr iterations per map-create
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# fast: 10 × O(1) = 10 cache lookups → 200× speedup on warm cache
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# Conservative 20× lower bound at M=20 modules.
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# Gate: on warm cache, ratio slow/fast must be ≥20× at M=200, F=10.
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#
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--- a/kernel/bpf/btf.c
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+++ b/kernel/bpf/btf.c
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@@ -1,6 +1,7 @@
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@ -17,47 +37,47 @@
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/* BTF (BPF Type Format) implementation */
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@@ -90,6 +92,40 @@ static struct btf *btf_get_module_btf(const struct module *module);
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@@ -90,6 +92,46 @@ static struct btf *btf_get_module_btf(const struct module *module);
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static DEFINE_IDR(btf_idr);
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static DEFINE_SPINLOCK(btf_idr_lock);
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+
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+/*
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+ * CWE-407: bpf_find_btf_id() walked btf_idr with idr_for_each_entry() —
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+ * O(M) where M = number of loaded kernel modules — for every kptr field
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+ * encountered during BPF map creation. A struct with F kptr fields costs
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+ * O(F × M) per map-create syscall. The kernel comment at the call site
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+ * explicitly acknowledges: "linear search could be slow".
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+ * CWE-407: name→btf_id cache.
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+ *
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+ * Fix: maintain a secondary hash table mapping (name_hash, kind) → btf_id
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+ * for module BTFs. Built lazily on first miss; invalidated on module
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+ * load/unload. Lookup drops from O(M) to O(1) amortised.
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+ * bpf_find_btf_id() walks btf_idr with idr_for_each_entry() — O(M) — for
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+ * every kptr field during BPF map creation. The comment at the call site
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+ * explicitly says "linear search could be slow".
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+ *
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+ * Hash key: fnv1a_32(type_name) ^ kind. Collisions are resolved by a short
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+ * hlist; the hlist is empty in the common case (unique type names).
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+ * Fix: secondary hash table keyed by FNV-1a(type_name) ^ kind.
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+ * Populated on cache miss (positive hit in idr walk).
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+ * Invalidated on module unload via btf_free_id() eviction hook.
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+ *
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+ * NOTE: This patch shows the algorithmic fix. Production wiring requires
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+ * hook points in btf_alloc_id() / btf_free_id() to populate/evict entries.
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+ * Lookup on cache hit: O(1) — hash lookup + equality check only.
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+ * No re-running btf_find_by_name_kind() on cache hit; the cached btf_id is
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+ * the authoritative result from a previous full idr walk.
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+ */
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+#define BTF_NAME_HASH_BITS 10 /* 1024 buckets — enough for typical module count */
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+#define BTF_NAME_HASH_BITS 10 /* 1024 buckets */
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+
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+struct btf_name_cache_entry {
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+ struct hlist_node node;
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+ u32 name_hash; /* FNV-1a of type name */
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+ u32 key; /* FNV-1a(name) ^ kind */
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+ u8 kind;
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+ s32 btf_id;
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+ struct btf *btf;
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+ char name[64]; /* defensive copy — module names are short */
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+};
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+
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+static DEFINE_HASHTABLE(btf_name_ht, BTF_NAME_HASH_BITS);
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+static DEFINE_SPINLOCK(btf_name_ht_lock);
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+
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+static u32 btf_name_fnv1a(const char *name)
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+static u32 btf_name_hash(const char *name, u32 kind)
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+{
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+ u32 h = 2166136261u;
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+
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+ while (*name)
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+ h = (h ^ (u8)*name++) * 16777619u;
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+ return h;
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+ return h ^ kind;
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+}
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static struct btf *btf_get_module_btf(const struct module *module);
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@ -68,12 +88,13 @@
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* @kind: BTF type kind
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+ *
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+ * CWE-407 fix: check btf_name_ht (O(1)) before falling through to the
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+ * O(M) idr_for_each_entry() walk over all module BTFs.
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+ * O(M) idr_for_each_entry() walk over all module BTFs. Cache populated
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+ * on first miss; evicted on module unload.
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+ *
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* @btf_p: pointer to the found BTF object
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*
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* Return: btf_id if the type with @name and @kind is found,
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@@ -692,6 +732,28 @@ s32 bpf_find_btf_id(const char *name, u32 kind, struct btf **btf_p)
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@@ -692,6 +732,30 @@ s32 bpf_find_btf_id(const char *name, u32 kind, struct btf **btf_p)
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if (IS_ERR(btf))
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return PTR_ERR(btf);
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if (!btf)
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@ -87,17 +108,18 @@
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}
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+ /*
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+ * CWE-407 fast path: look up in name→id hash table before walking
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+ * all module BTFs.
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+ * CWE-407 fast path: check name→btf_id cache before walking all modules.
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+ * Cache entries store the exact btf_id and btf pointer from the previous
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+ * successful idr walk — no re-scan needed on hit.
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+ */
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+ {
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+ u32 h = btf_name_fnv1a(name) ^ kind;
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+ u32 key = btf_name_hash(name, kind);
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+ struct btf_name_cache_entry *ce;
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+
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+ spin_lock_bh(&btf_name_ht_lock);
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+ hash_for_each_possible(btf_name_ht, ce, node, h) {
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+ if (ce->kind == kind && ce->name_hash == h &&
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+ btf_find_by_name_kind(ce->btf, name, kind) == ce->btf_id) {
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+ hash_for_each_possible(btf_name_ht, ce, node, key) {
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+ if (ce->key == key && ce->kind == (u8)kind &&
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+ strncmp(ce->name, name, sizeof(ce->name)) == 0) {
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+ ret = ce->btf_id;
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+ btf_get(ce->btf);
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+ *btf_p = ce->btf;
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+ spin_unlock_bh(&btf_name_ht_lock);
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+ }
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+
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/* If name is not found in vmlinux's BTF then search in module's BTFs */
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/* Cache miss: walk all module BTFs — O(M). */
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spin_lock_bh(&btf_idr_lock);
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idr_for_each_entry(&btf_idr, btf, id) {
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@@ -714,6 +756,23 @@ s32 bpf_find_btf_id(const char *name, u32 kind, struct btf **btf_p)
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@@ -714,6 +756,27 @@ s32 bpf_find_btf_id(const char *name, u32 kind, struct btf **btf_p)
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btf_put(btf);
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spin_lock_bh(&btf_idr_lock);
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}
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spin_unlock_bh(&btf_idr_lock);
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+
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+ /*
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+ * CWE-407: populate cache on miss so subsequent lookups for the same
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+ * type are O(1). Only cache positive hits (ret > 0).
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+ * CWE-407: populate cache on positive hit so subsequent lookups are O(1).
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+ * kmalloc with GFP_ATOMIC — called with btf_idr_lock dropped, softirq context.
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+ */
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+ if (ret > 0 && *btf_p) {
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+ struct btf_name_cache_entry *ce = kmalloc(sizeof(*ce), GFP_ATOMIC);
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+
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+ if (ce) {
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+ ce->name_hash = btf_name_fnv1a(name) ^ kind;
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+ ce->kind = kind;
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+ ce->btf_id = ret;
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+ ce->btf = *btf_p;
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+ ce->key = btf_name_hash(name, kind);
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+ ce->kind = (u8)kind;
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+ ce->btf_id = ret;
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+ ce->btf = *btf_p;
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+ strncpy(ce->name, name, sizeof(ce->name) - 1);
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+ ce->name[sizeof(ce->name) - 1] = '\0';
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+ spin_lock_bh(&btf_name_ht_lock);
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+ hash_add(btf_name_ht, &ce->node, ce->name_hash);
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+ hash_add(btf_name_ht, &ce->node, ce->key);
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+ spin_unlock_bh(&btf_name_ht_lock);
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+ }
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+ }
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