From 5a58ed152fd62fe3b932ea2d503b1b45ae8838d7 Mon Sep 17 00:00:00 2001 From: Jorg Sowa Date: Wed, 27 May 2026 20:08:36 +0200 Subject: [PATCH 1/2] fix: session GC fork --- ext/session/php_session.h | 2 ++ ext/session/session.c | 22 ++++++++-------------- 2 files changed, 10 insertions(+), 14 deletions(-) diff --git a/ext/session/php_session.h b/ext/session/php_session.h index dfa7632e5a44..0b0ba5efbeca 100644 --- a/ext/session/php_session.h +++ b/ext/session/php_session.h @@ -157,6 +157,8 @@ typedef struct _php_ps_globals { zend_string *session_started_filename; uint32_t session_started_lineno; int module_number; + /* Unused since the GC probability draw was made stateless; retained only + * to preserve struct layout (ABI) on stable branches. */ php_random_status_state_pcgoneseq128xslrr64 random_state; php_random_algo_with_state random; zend_long gc_probability; diff --git a/ext/session/session.c b/ext/session/session.c index 70e1673d87f5..cdca09a1d274 100644 --- a/ext/session/session.c +++ b/ext/session/session.c @@ -394,7 +394,14 @@ static zend_long php_session_gc(bool immediate) /* {{{ */ /* GC must be done before reading session data. */ if ((PS(mod_data) || PS(mod_user_implemented))) { if (!collect && PS(gc_probability) > 0) { - collect = php_random_range(PS(random), 0, PS(gc_divisor) - 1) < PS(gc_probability); + /* Draw fresh entropy per request instead of using the per-process + * PS(random) state. The latter is seeded once in GINIT, which runs + * before SAPIs such as PHP-FPM fork their workers, so every worker + * would inherit and replay the same GC-decision sequence. */ + uint32_t rand_val; + if (php_random_bytes_silent(&rand_val, sizeof(rand_val)) == SUCCESS) { + collect = (rand_val % (uint32_t) PS(gc_divisor)) < (uint32_t) PS(gc_probability); + } } if (collect) { @@ -2979,19 +2986,6 @@ static PHP_GINIT_FUNCTION(ps) /* {{{ */ ZVAL_UNDEF(&ps_globals->mod_user_names.ps_validate_sid); ZVAL_UNDEF(&ps_globals->mod_user_names.ps_update_timestamp); ZVAL_UNDEF(&ps_globals->http_session_vars); - - ps_globals->random = (php_random_algo_with_state){ - .algo = &php_random_algo_pcgoneseq128xslrr64, - .state = &ps_globals->random_state, - }; - php_random_uint128_t seed; - if (php_random_bytes_silent(&seed, sizeof(seed)) == FAILURE) { - seed = php_random_uint128_constant( - php_random_generate_fallback_seed(), - php_random_generate_fallback_seed() - ); - } - php_random_pcgoneseq128xslrr64_seed128(ps_globals->random.state, seed); } /* }}} */ From b51f15ec4d9a6896c21e0e8405f213670ebde100 Mon Sep 17 00:00:00 2001 From: Jorg Sowa Date: Wed, 10 Jun 2026 22:59:35 +0200 Subject: [PATCH 2/2] fix: seed session GC RNG lazily per worker process --- ext/session/php_session.h | 3 +-- ext/session/session.c | 25 ++++++++++++++++++------- 2 files changed, 19 insertions(+), 9 deletions(-) diff --git a/ext/session/php_session.h b/ext/session/php_session.h index 0b0ba5efbeca..4f958bb8b82f 100644 --- a/ext/session/php_session.h +++ b/ext/session/php_session.h @@ -157,8 +157,6 @@ typedef struct _php_ps_globals { zend_string *session_started_filename; uint32_t session_started_lineno; int module_number; - /* Unused since the GC probability draw was made stateless; retained only - * to preserve struct layout (ABI) on stable branches. */ php_random_status_state_pcgoneseq128xslrr64 random_state; php_random_algo_with_state random; zend_long gc_probability; @@ -205,6 +203,7 @@ typedef struct _php_ps_globals { bool in_save_handler; /* state if session is in save handler or not */ bool set_handler; /* state if session module i setting handler or not */ zend_string *session_vars; /* serialized original session data */ + bool random_seeded; } php_ps_globals; typedef php_ps_globals zend_ps_globals; diff --git a/ext/session/session.c b/ext/session/session.c index cdca09a1d274..ba71d709a536 100644 --- a/ext/session/session.c +++ b/ext/session/session.c @@ -394,14 +394,19 @@ static zend_long php_session_gc(bool immediate) /* {{{ */ /* GC must be done before reading session data. */ if ((PS(mod_data) || PS(mod_user_implemented))) { if (!collect && PS(gc_probability) > 0) { - /* Draw fresh entropy per request instead of using the per-process - * PS(random) state. The latter is seeded once in GINIT, which runs - * before SAPIs such as PHP-FPM fork their workers, so every worker - * would inherit and replay the same GC-decision sequence. */ - uint32_t rand_val; - if (php_random_bytes_silent(&rand_val, sizeof(rand_val)) == SUCCESS) { - collect = (rand_val % (uint32_t) PS(gc_divisor)) < (uint32_t) PS(gc_probability); + /* Seed lazily on first GC draw per process. */ + if (UNEXPECTED(!PS(random_seeded))) { + php_random_uint128_t seed; + if (php_random_bytes_silent(&seed, sizeof(seed)) == FAILURE) { + seed = php_random_uint128_constant( + php_random_generate_fallback_seed(), + php_random_generate_fallback_seed() + ); + } + php_random_pcgoneseq128xslrr64_seed128(PS(random).state, seed); + PS(random_seeded) = true; } + collect = php_random_range(PS(random), 0, PS(gc_divisor) - 1) < PS(gc_probability); } if (collect) { @@ -2986,6 +2991,12 @@ static PHP_GINIT_FUNCTION(ps) /* {{{ */ ZVAL_UNDEF(&ps_globals->mod_user_names.ps_validate_sid); ZVAL_UNDEF(&ps_globals->mod_user_names.ps_update_timestamp); ZVAL_UNDEF(&ps_globals->http_session_vars); + + ps_globals->random = (php_random_algo_with_state){ + .algo = &php_random_algo_pcgoneseq128xslrr64, + .state = &ps_globals->random_state, + }; + ps_globals->random_seeded = false; } /* }}} */