[dpdk-dev] [PATCH] eal: fix possible UB on creation of ctrl thread

[Luc Pelletier]

The creation of control threads uses a pthread barrier for
synchronization. This patch fixes a race condition where the pthread
barrier could get destroyed while one of the threads has not yet
returned from the pthread_barrier_wait function, which could result in
undefined behaviour.

Fixes: 3a0d465d4c53 ("eal: fix use-after-free on control thread creation")
Cc: jianfeng....@intel.com
Cc: sta...@dpdk.org

Signed-off-by: Luc Pelletier <lucp.at.w...@gmail.com>
---
 lib/librte_eal/common/eal_common_thread.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/lib/librte_eal/common/eal_common_thread.c 
b/lib/librte_eal/common/eal_common_thread.c
index 73a055902..bd9a9fdbc 100644
--- a/lib/librte_eal/common/eal_common_thread.c
+++ b/lib/librte_eal/common/eal_common_thread.c
@@ -170,6 +170,7 @@ struct rte_thread_ctrl_params {
        void *(*start_routine)(void *);
        void *arg;
        pthread_barrier_t configured;
+       bool barrier_in_use;
 };
 
 static void *ctrl_thread_init(void *arg)
@@ -186,9 +187,13 @@ static void *ctrl_thread_init(void *arg)
 
        ret = pthread_barrier_wait(&params->configured);
        if (ret == PTHREAD_BARRIER_SERIAL_THREAD) {
+               while (__atomic_load_n(&params->barrier_in_use,
+                                      __ATOMIC_ACQUIRE))
+                       sched_yield();
                pthread_barrier_destroy(&params->configured);
                free(params);
-       }
+       } else
+               __atomic_store_n(&params->barrier_in_use, 0, __ATOMIC_RELEASE);
 
        return start_routine(routine_arg);
 }
@@ -210,6 +215,7 @@ rte_ctrl_thread_create(pthread_t *thread, const char *name,
 
        params->start_routine = start_routine;
        params->arg = arg;
+       params->barrier_in_use = 1;
 
        pthread_barrier_init(&params->configured, NULL, 2);
 
@@ -232,18 +238,26 @@ rte_ctrl_thread_create(pthread_t *thread, const char 
*name,
 
        ret = pthread_barrier_wait(&params->configured);
        if (ret == PTHREAD_BARRIER_SERIAL_THREAD) {
+               while (__atomic_load_n(&params->barrier_in_use,
+                                      __ATOMIC_ACQUIRE))
+                       sched_yield();
                pthread_barrier_destroy(&params->configured);
                free(params);
-       }
+       } else
+               __atomic_store_n(&params->barrier_in_use, 0, __ATOMIC_RELEASE);
 
        return 0;
 
 fail:
        if (PTHREAD_BARRIER_SERIAL_THREAD ==
            pthread_barrier_wait(&params->configured)) {
+               while (__atomic_load_n(&params->barrier_in_use,
+                                      __ATOMIC_ACQUIRE))
+                       sched_yield();
                pthread_barrier_destroy(&params->configured);
                free(params);
-       }
+       } else
+               __atomic_store_n(&params->barrier_in_use, 0, __ATOMIC_RELEASE);
        pthread_cancel(*thread);
        pthread_join(*thread, NULL);
        return -ret;
-- 
2.25.1