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BUG/MINOR: resolvers: switch to a better PRNG for query IDs

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The PRNG used by the DNS currently is easily predictable once an
observer can collect a few consecutive IDs from the same thread, since
it's a 32-bit xorshift reduced to 16 bits output. Let's switch it to
ha_random32() instead.

This should be backported, however on older releases the ha_random32()
cost is higher due to the lock involved.
This commit is contained in:
Willy Tarreau 2026-05-26 09:30:12 +02:00
parent c41c731f5e
commit 2a47cab7f3
1 changed files with 1 additions and 14 deletions
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15
src/resolvers.c
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@ -63,7 +63,6 @@ struct list resolv_srvrq_list = LIST_HEAD_INIT(resolv_srvrq_list);
static THREAD_LOCAL struct list death_row; /* list of deferred resolutions to kill, local validity only */
static THREAD_LOCAL unsigned int recurse = 0; /* counter to track calls to public functions */
static THREAD_LOCAL uint64_t resolv_query_id_seed = 0; /* random seed */
struct resolvers *curr_resolvers = NULL;
DECLARE_STATIC_TYPED_POOL(resolv_answer_item_pool, "resolv_answer_item", struct resolv_answer_item);
@ -365,18 +364,6 @@ struct resolv_answer_item *find_srvrq_answer_record(const struct resolv_requeste
return NULL;
}
/* 2 bytes random generator to generate DNS query ID */
static inline uint16_t resolv_rnd16(void)
{
if (!resolv_query_id_seed)
resolv_query_id_seed = now_ms;
resolv_query_id_seed ^= resolv_query_id_seed << 13;
resolv_query_id_seed ^= resolv_query_id_seed >> 7;
resolv_query_id_seed ^= resolv_query_id_seed << 17;
return resolv_query_id_seed;
}
static inline int resolv_resolution_timeout(struct resolv_resolution *res)
{
return (!LIST_ISEMPTY(&res->requesters) ? res->resolvers->timeout.resolve : res->resolvers->hold.valid);
@ -516,7 +503,7 @@ resolv_run_resolution(struct resolv_resolution *resolution)
/* Generates a new query id. We try at most 100 times to find a free
* query id */
for (i = 0; i < 100; ++i) {
query_id = resolv_rnd16();
query_id = (uint16_t)ha_random32();
if (!eb32_lookup(&resolvers->query_ids, query_id))
break;
query_id = -1;