From 2cca77ee01343bf080f1b70f0217a84c200fe7c1 Mon Sep 17 00:00:00 2001 From: Mark Johnston Date: Fri, 14 May 2021 10:07:56 -0400 Subject: kqueue timer: Remove detached knotes from the process stop queue There are some scenarios where a timer event may be detached when it is on the process' kqueue timer stop queue. If kqtimer_proc_continue() is called after that point, it will iterate over the queue and access freed timer structures. It is also possible, at least in a multithreaded program, for a stopped timer event to be scheduled without removing it from the process' stop queue. Ensure that we do not doubly enqueue the event structure in this case. Reported by: syzbot+cea0931bb4e34cd728bd@syzkaller.appspotmail.com Reported by: syzbot+9e1a2f3734652015998c@syzkaller.appspotmail.com Reviewed by: kib MFC after: 1 week Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D30251 --- sys/kern/kern_event.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c index 1067e7f128b7..e7047e9a7ad9 100644 --- a/sys/kern/kern_event.c +++ b/sys/kern/kern_event.c @@ -680,11 +680,14 @@ struct kq_timer_cb_data { struct proc *p; struct knote *kn; int cpuid; + int flags; TAILQ_ENTRY(kq_timer_cb_data) link; sbintime_t next; /* next timer event fires at */ sbintime_t to; /* precalculated timer period, 0 for abs */ }; +#define KQ_TIMER_CB_ENQUEUED 0x01 + static void kqtimer_sched_callout(struct kq_timer_cb_data *kc) { @@ -706,6 +709,7 @@ kqtimer_proc_continue(struct proc *p) TAILQ_FOREACH_SAFE(kc, &p->p_kqtim_stop, link, kc1) { TAILQ_REMOVE(&p->p_kqtim_stop, kc, link); + kc->flags &= ~KQ_TIMER_CB_ENQUEUED; if (kc->next <= now) filt_timerexpire_l(kc->kn, true); else @@ -753,7 +757,10 @@ filt_timerexpire_l(struct knote *kn, bool proc_locked) if (!proc_locked) PROC_LOCK(p); if (P_SHOULDSTOP(p) || P_KILLED(p)) { - TAILQ_INSERT_TAIL(&p->p_kqtim_stop, kc, link); + if ((kc->flags & KQ_TIMER_CB_ENQUEUED) == 0) { + kc->flags |= KQ_TIMER_CB_ENQUEUED; + TAILQ_INSERT_TAIL(&p->p_kqtim_stop, kc, link); + } if (!proc_locked) PROC_UNLOCK(p); return; @@ -826,6 +833,7 @@ filt_timerattach(struct knote *kn) kc->kn = kn; kc->p = curproc; kc->cpuid = PCPU_GET(cpuid); + kc->flags = 0; callout_init(&kc->c, 1); filt_timerstart(kn, to); @@ -856,6 +864,11 @@ filt_timerdetach(struct knote *kn) kc = kn->kn_ptr.p_v; callout_drain(&kc->c); + if ((kc->flags & KQ_TIMER_CB_ENQUEUED) != 0) { + PROC_LOCK(kc->p); + TAILQ_REMOVE(&kc->p->p_kqtim_stop, kc, link); + PROC_UNLOCK(kc->p); + } free(kc, M_KQUEUE); old = atomic_fetchadd_int(&kq_ncallouts, -1); KASSERT(old > 0, ("Number of callouts cannot become negative")); -- cgit v1.2.3