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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)
66 lines
1.5 KiB
C++
66 lines
1.5 KiB
C++
/*
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* Copyright (C) 2018-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 "auth/passwords.hh"
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#include <cerrno>
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extern "C" {
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#include <crypt.h>
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#include <unistd.h>
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}
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namespace auth::passwords {
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static thread_local crypt_data tlcrypt = {};
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namespace detail {
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void verify_scheme(scheme scheme) {
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const sstring random_part_of_salt = "aaaabbbbccccdddd";
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const sstring salt = sstring(prefix_for_scheme(scheme)) + random_part_of_salt;
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const char* e = crypt_r("fisk", salt.c_str(), &tlcrypt);
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if (e && (e[0] != '*')) {
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return;
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}
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throw no_supported_schemes();
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}
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sstring hash_with_salt(const sstring& pass, const sstring& salt) {
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auto res = crypt_r(pass.c_str(), salt.c_str(), &tlcrypt);
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if (!res || (res[0] == '*')) {
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throw std::system_error(errno, std::system_category());
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}
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return res;
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}
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std::string_view prefix_for_scheme(scheme c) noexcept {
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switch (c) {
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case scheme::bcrypt_y: return "$2y$";
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case scheme::bcrypt_a: return "$2a$";
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case scheme::sha_512: return "$6$";
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case scheme::sha_256: return "$5$";
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case scheme::md5: return "$1$";
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}
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}
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} // namespace detail
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no_supported_schemes::no_supported_schemes()
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: std::runtime_error("No allowed hashing schemes are supported on this system") {
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}
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bool check(const sstring& pass, const sstring& salted_hash) {
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return detail::hash_with_salt(pass, salted_hash) == salted_hash;
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}
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} // namespace auth::passwords
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