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Mitigate hashtable bucket collision attacks #120

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Mitigate hashtable bucket collision attacks #120

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18 changes: 17 additions & 1 deletion code/header/essentials/collections/hashtable.h
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,15 @@ typedef struct zpl_hash_table_find_result {
zpl_isize entry_index;
} zpl_hash_table_find_result;

ZPL_IMPL_INLINE zpl_u64 zpl__hash_table_mix_key(zpl_u64 key) {
key ^= key >> 33;
key *= 0xff51afd7ed558ccdull;
key ^= key >> 33;
key *= 0xc4ceb9fe1a85ec53ull;
key ^= key >> 33;
return key;
}

/**
* Combined macro for a quick delcaration + definition
*/
Expand All @@ -60,6 +69,7 @@ typedef struct zpl_hash_table_find_result {
typedef struct NAME { \
zpl_array(zpl_isize) hashes; \
zpl_array(ZPL_JOIN2(NAME, Entry)) entries; \
zpl_u64 seed; \
} NAME; \
\
PREFIX void ZPL_JOIN2(FUNC, init) (NAME *h, zpl_allocator a); \
Expand All @@ -84,6 +94,9 @@ typedef struct zpl_hash_table_find_result {
void ZPL_JOIN2(FUNC, init)(NAME * h, zpl_allocator a) { \
zpl_array_init(h->hashes, a); \
zpl_array_init(h->entries, a); \
h->seed = zpl__hash_table_mix_key(cast(zpl_u64)cast(zpl_uintptr)h ^ \
cast(zpl_u64)cast(zpl_uintptr)h->hashes ^ \
cast(zpl_u64)cast(zpl_uintptr)h->entries); \
} \
\
void ZPL_JOIN2(FUNC, destroy)(NAME * h) { \
Expand Down Expand Up @@ -118,7 +131,8 @@ typedef struct zpl_hash_table_find_result {
zpl_internal zpl_hash_table_find_result ZPL_JOIN2(FUNC, _find)(NAME * h, zpl_u64 key) { \
zpl_hash_table_find_result r = { -1, -1, -1 }; \
if (zpl_array_count(h->hashes) > 0) { \
r.hash_index = key % zpl_array_count(h->hashes); \
r.hash_index = cast(zpl_isize)(zpl__hash_table_mix_key(key ^ h->seed) % \
cast(zpl_u64)zpl_array_count(h->hashes)); \
r.entry_index = h->hashes[r.hash_index]; \
while (r.entry_index >= 0) { \
if (h->entries[r.entry_index].key == key) return r; \
Expand All @@ -142,6 +156,7 @@ typedef struct zpl_hash_table_find_result {
zpl_isize i, j; \
NAME nh = { 0 }; \
ZPL_JOIN2(FUNC, init)(&nh, zpl_array_allocator(h->hashes)); \
nh.seed = h->seed; \
zpl_array_resize(nh.hashes, new_count); \
zpl_array_reserve(nh.entries, zpl_array_count(h->entries)); \
for (i = 0; i < new_count; i++) nh.hashes[i] = -1; \
Expand All @@ -162,6 +177,7 @@ typedef struct zpl_hash_table_find_result {
ZPL_JOIN2(FUNC, destroy)(h); \
h->hashes = nh.hashes; \
h->entries = nh.entries; \
h->seed = nh.seed; \
} \
\
void ZPL_JOIN2(FUNC, rehash_fast)(NAME * h) { \
Expand Down
24 changes: 24 additions & 0 deletions code/tests/cases/table.h
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Original file line number Diff line number Diff line change
Expand Up @@ -47,4 +47,28 @@ MODULE(table, {

unit_table_destroy(&t1);
});

IT("should mix keys before bucket assignment", {
unit_table t1 = {0};
unit_table_init(&t1, zpl_heap());
t1.seed = 0;
unit_table_rehash(&t1, 64);

for (int i = 0; i < 16; ++i) {
unit_table_set(&t1, cast(zpl_u64)(i * 64), i);
}

zpl_isize bucket_zero_count = 0;
for (zpl_isize idx = t1.hashes[0]; idx >= 0; idx = t1.entries[idx].next) {
bucket_zero_count++;
}

LESSER(bucket_zero_count, 16);

for (int i = 0; i < 16; ++i) {
EQUALS(i, *unit_table_get(&t1, cast(zpl_u64)(i * 64)));
}

unit_table_destroy(&t1);
});
});