[dpdk-dev] [PATCH v6] eal: fix race in ctrl thread creation

[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>
---

Hi Olivier,

I've made the changes as you requested. However, I'm using the atomic
built-ins for reading and writing start_routine; I think they're
required to prevent any re-reordering.

Please let me know what you think.

 lib/librte_eal/common/eal_common_thread.c | 63 +++++++++++++----------
 1 file changed, 35 insertions(+), 28 deletions(-)

diff --git a/lib/librte_eal/common/eal_common_thread.c 
b/lib/librte_eal/common/eal_common_thread.c
index 73a055902..fcb386f77 100644
--- a/lib/librte_eal/common/eal_common_thread.c
+++ b/lib/librte_eal/common/eal_common_thread.c
@@ -170,25 +170,34 @@ struct rte_thread_ctrl_params {
        void *(*start_routine)(void *);
        void *arg;
        pthread_barrier_t configured;
+       unsigned int refcnt;
 };
 
+static void ctrl_params_free(struct rte_thread_ctrl_params *params)
+{
+       if (__atomic_sub_fetch(&params->refcnt, 1, __ATOMIC_ACQ_REL) == 0) {
+               pthread_barrier_destroy(&params->configured);
+               free(params);
+       }
+}
+
 static void *ctrl_thread_init(void *arg)
 {
-       int ret;
        struct internal_config *internal_conf =
                eal_get_internal_configuration();
        rte_cpuset_t *cpuset = &internal_conf->ctrl_cpuset;
        struct rte_thread_ctrl_params *params = arg;
-       void *(*start_routine)(void *) = params->start_routine;
+       void *(*start_routine)(void *);
        void *routine_arg = params->arg;
 
        __rte_thread_init(rte_lcore_id(), cpuset);
 
-       ret = pthread_barrier_wait(&params->configured);
-       if (ret == PTHREAD_BARRIER_SERIAL_THREAD) {
-               pthread_barrier_destroy(&params->configured);
-               free(params);
-       }
+       pthread_barrier_wait(&params->configured);
+       start_routine = __atomic_load_n(&params->start_routine, 
__ATOMIC_ACQUIRE);
+       ctrl_params_free(params);
+
+       if (start_routine == NULL)
+               return NULL;
 
        return start_routine(routine_arg);
 }
@@ -210,14 +219,15 @@ rte_ctrl_thread_create(pthread_t *thread, const char 
*name,
 
        params->start_routine = start_routine;
        params->arg = arg;
+       params->refcnt = 2;
 
-       pthread_barrier_init(&params->configured, NULL, 2);
+       ret = pthread_barrier_init(&params->configured, NULL, 2);
+       if (ret != 0)
+               goto fail_no_barrier;
 
        ret = pthread_create(thread, attr, ctrl_thread_init, (void *)params);
-       if (ret != 0) {
-               free(params);
-               return -ret;
-       }
+       if (ret != 0)
+               goto fail_with_barrier;
 
        if (name != NULL) {
                ret = rte_thread_setname(*thread, name);
@@ -227,25 +237,22 @@ rte_ctrl_thread_create(pthread_t *thread, const char 
*name,
        }
 
        ret = pthread_setaffinity_np(*thread, sizeof(*cpuset), cpuset);
-       if (ret)
-               goto fail;
+       if (ret != 0)
+               __atomic_store_n(&params->start_routine, NULL, 
__ATOMIC_RELEASE);
+       pthread_barrier_wait(&params->configured);
+       ctrl_params_free(params);
 
-       ret = pthread_barrier_wait(&params->configured);
-       if (ret == PTHREAD_BARRIER_SERIAL_THREAD) {
-               pthread_barrier_destroy(&params->configured);
-               free(params);
-       }
+       if (ret != 0)
+               pthread_join(*thread, NULL);
 
-       return 0;
+       return -ret;
+
+fail_with_barrier:
+       pthread_barrier_destroy(&params->configured);
+
+fail_no_barrier:
+       free(params);
 
-fail:
-       if (PTHREAD_BARRIER_SERIAL_THREAD ==
-           pthread_barrier_wait(&params->configured)) {
-               pthread_barrier_destroy(&params->configured);
-               free(params);
-       }
-       pthread_cancel(*thread);
-       pthread_join(*thread, NULL);
        return -ret;
 }
 
-- 
2.25.1