0900a88884
Analysis of customer stalls revealed that the function `detail::hash_with_salt` (invoked by `passwords::check`) often blocks the reactor. Internally, this function uses the external `crypt_r` function to compute password hashes, which is CPU-intensive.
This PR addresses the issue in two ways:
1) `sha-512` is now the only password hashing scheme for new passwords (it was already the common-case).
2) `passwords::check` is moved to a dedicated alien thread.
Regarding point 1: before this change, the following hashing schemes were supported by `identify_best_supported_scheme()`: bcrypt_y, bcrypt_a, SHA-512, SHA-256, and MD5. The reason for this was that the `crypt_r` function used for password hashing comes from an external library (currently `libxcrypt`), and the supported hashing algorithms vary depending on the library in use. However:
- The bcrypt schemes never worked properly because their prefixes lack the required round count (e.g. `$2y$` instead of `$2y$05$`). Moreover, bcrypt is slower than SHA-512, so it not good idea to fix or use it.
- SHA-256 and SHA-512 both belong to the SHA-2 family. Libraries that support one almost always support the other, so it’s very unlikely to find SHA-256 without SHA-512.
- MD5 is no longer considered secure for password hashing.
Regarding point 2: the `passwords::check` call now runs on a shared alien thread created at database startup. An `std::mutex` synchronizes that thread with the shards. In theory this could introduce a frequent lock contention, but in practice each shard handles only a few hundred new connections per second—even during storms. There is already `_conns_cpu_concurrency_semaphore` in `generic_server` limits the number of concurrent connection handlers.
Fixes https://github.com/scylladb/scylladb/issues/24524
Backport not needed, as it is a new feature.
Closes scylladb/scylladb#24924
* github.com:scylladb/scylladb:
main: utils: add thread names to alien workers
auth: move passwords::check call to alien thread
test: wait for 3 clients with given username in test_service_level_api
auth: refactor password checking in password_authenticator
auth: make SHA-512 the only password hashing scheme for new passwords
auth: whitespace change in identify_best_supported_scheme()
auth: require scheme as parameter for `generate_salt`
auth: check password hashing scheme support on authenticator start
(cherry picked from commit c762425ea7)
71 lines
2.1 KiB
C++
71 lines
2.1 KiB
C++
/*
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* Copyright (C) 2024-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
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*/
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#include "utils/alien_worker.hh"
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#include <seastar/util/log.hh>
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using namespace seastar;
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namespace utils {
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std::thread alien_worker::spawn(seastar::logger& log, int niceness, const seastar::sstring& name_suffix) {
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sigset_t newset;
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sigset_t oldset;
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sigfillset(&newset);
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auto r = ::pthread_sigmask(SIG_SETMASK, &newset, &oldset);
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assert(r == 0);
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auto thread_name = fmt::format("alien-{}", name_suffix);
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if (thread_name.size() > 15) {
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log.warn("Thread name '{}' is longer than 15 characters, truncating to fit", thread_name);
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thread_name.resize(15); // pthread_setname_np requires name to be <= 15 characters
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}
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auto thread = std::thread([this, &log, niceness, thread_name] () noexcept {
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errno = 0;
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int setname_value = pthread_setname_np(pthread_self(), thread_name.c_str());
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if (setname_value != 0) {
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log.error("Unable to set worker thread name '{}', setname_value={}", thread_name, setname_value);
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std::abort();
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}
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int nice_value = nice(niceness);
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if (nice_value == -1 && errno != 0) {
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log.warn("Unable to renice worker thread (system error number {}); the thread will compete with reactor, which can cause latency spikes. Try adding CAP_SYS_NICE", errno);
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}
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while (true) {
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std::unique_lock lk(_mut);
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_cv.wait(lk, [this] { return !_pending.empty() || !_running; });
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if (!_running) {
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return;
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}
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auto f = std::move(_pending.front());
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_pending.pop();
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lk.unlock();
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f();
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}
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});
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r = ::pthread_sigmask(SIG_SETMASK, &oldset, nullptr);
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assert(r == 0);
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return thread;
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}
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alien_worker::alien_worker(seastar::logger& log, int niceness, const seastar::sstring& name_suffix)
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: _thread(spawn(log, niceness, name_suffix))
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{}
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alien_worker::~alien_worker() {
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{
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std::unique_lock lk(_mut);
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_running = false;
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}
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_cv.notify_one();
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_thread.join();
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}
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} // namespace utils
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