fix multiple bugs in SIGEV_THREAD timers

1. the thread result field was reused for storing a kernel timer id,
but would be overwritten if the application code exited or cancelled
the thread.

2. low pointer values were used as the indicator that the timer id is
a kernel timer id rather than a thread id. this is not portable, as
mmap may return low pointers on some conditions. instead, use the fact
that pointers must be aligned and kernel timer ids must be
non-negative to map pointers into the negative integer space.

3. signals were not blocked until after the timer thread started, so a
race condition could allow a signal handler to run in the timer thread
when it's not supposed to exist. this is mainly problematic if the
calling thread was the only thread where the signal was unblocked and
the signal handler assumes it runs in that thread.

1 files changed, 15 insertions, 14 deletions

diff --git a/src/time/timer_create.c b/src/time/timer_create.c
index f76b9ef8..2b4619d4 100644
--- a/src/time/timer_create.c
+++ b/src/time/timer_create.c
@@ -60,20 +60,18 @@ static void *start(void *arg)
 {
 	pthread_t self = __pthread_self();
 	struct start_args *args = arg;
-	sigset_t set;
+	int id;
 
 	/* Reuse no-longer-needed thread structure fields to avoid
 	 * needing the timer address in the signal handler. */
 	self->start = (void *(*)(void *))args->sev->sigev_notify_function;
 	self->start_arg = args->sev->sigev_value.sival_ptr;
-	self->result = (void *)-1;
-
-	sigfillset(&set);
-	pthread_sigmask(SIG_BLOCK, &set, 0);
 
 	pthread_barrier_wait(&args->b);
-	__wait(&self->delete_timer, 0, 0, 1);
-	__syscall(SYS_timer_delete, self->result);
+	if ((id = self->timer_id) >= 0) {
+		__wait(&self->timer_id, 0, id, 1);
+		__syscall(SYS_timer_delete, id);
+	}
 	return 0;
 }
 
@@ -86,6 +84,7 @@ int timer_create(clockid_t clk, struct sigevent *restrict evp, timer_t *restrict
 	struct start_args args;
 	struct ksigevent ksev, *ksevp=0;
 	int timerid;
+	sigset_t set;
 
 	switch (evp ? evp->sigev_notify : SIGEV_SIGNAL) {
 	case SIGEV_NONE:
@@ -110,23 +109,25 @@ int timer_create(clockid_t clk, struct sigevent *restrict evp, timer_t *restrict
 		pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
 		pthread_barrier_init(&args.b, 0, 2);
 		args.sev = evp;
+
+		__block_app_sigs(&set);
 		r = pthread_create(&td, &attr, start, &args);
+		__restore_sigs(&set);
 		if (r) {
 			errno = r;
 			return -1;
 		}
+
 		ksev.sigev_value.sival_ptr = 0;
 		ksev.sigev_signo = SIGTIMER;
 		ksev.sigev_notify = 4; /* SIGEV_THREAD_ID */
 		ksev.sigev_tid = td->tid;
-		r = syscall(SYS_timer_create, clk, &ksev, &timerid);
+		if (syscall(SYS_timer_create, clk, &ksev, &timerid) < 0)
+			timerid = -1;
+		td->timer_id = timerid;
 		pthread_barrier_wait(&args.b);
-		if (r < 0) {
-			pthread_cancel(td);
-			return -1;
-		}
-		td->result = (void *)(intptr_t)timerid;
-		*res = td;
+		if (timerid < 0) return -1;
+		*res = (void *)(INTPTR_MIN | (uintptr_t)td>>1);
 		break;
 	default:
 		errno = EINVAL;