Hi Jens, This is the follow up patchset for the recent issue found in recv-msgall.c. There are two patches in this series. 1. Fix undefined behavior in `recv_prep()`. The lifetime of `struct msghdr msg;` must be long enough until the CQE is generated because the recvmsg operation will write to that storage. I found this test segfault when compiling with -O0 optimization. This is undefined behavior and may behave randomly. Fix this by making the lifetime of `struct msghdr msg;` long enough. 2. Fix invalid mutex usage. Calling pthread_mutex_lock() twice with the same mutex in the same thread without unlocking it first is invalid. The intention behind this pattern was to wait for the recv_fn() thread to be ready. Use the pthread barrier instead. It is more straightforward and correct. Please apply! Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org> --- Ammar Faizi (2): recv-msgall: Fix undefined behavior in `recv_prep()` recv-msgall: Fix invalid mutex usage test/recv-msgall.c | 44 +++++++++++++++++++++----------------------- 1 file changed, 21 insertions(+), 23 deletions(-) base-commit: 4961ac480052089a94978e9f771d513551aff61b -- Ammar Faizi
The lifetime of `struct msghdr msg;` must be long enough until the CQE is generated because the recvmsg operation will write to that storage. I found this test segfault when compiling with -O0 optimization. This is undefined behavior and may behave randomly. Fix this by making the lifetime of `struct msghdr msg;` long enough. Fixes: https://github.com/axboe/liburing/issues/855 Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org> --- test/recv-msgall.c | 28 +++++++++++++++------------- 1 file changed, 15 insertions(+), 13 deletions(-) diff --git a/test/recv-msgall.c b/test/recv-msgall.c index ae123e4c381b2b1a..f809834b2e427fc5 100644 --- a/test/recv-msgall.c +++ b/test/recv-msgall.c @@ -18,14 +18,18 @@ #define MAX_MSG 128 #define HOST "127.0.0.1" static __be16 bind_port; +struct recv_data { + pthread_mutex_t mutex; + int use_recvmsg; + struct msghdr msg; +}; static int recv_prep(struct io_uring *ring, struct iovec *iov, int *sock, - int use_recvmsg) + struct recv_data *rd) { struct sockaddr_in saddr; struct io_uring_sqe *sqe; int sockfd, ret, val; - struct msghdr msg = { }; memset(&saddr, 0, sizeof(saddr)); saddr.sin_family = AF_INET; @@ -47,14 +51,17 @@ static int recv_prep(struct io_uring *ring, struct iovec *iov, int *sock, bind_port = saddr.sin_port; sqe = io_uring_get_sqe(ring); - if (!use_recvmsg) { + if (!rd->use_recvmsg) { io_uring_prep_recv(sqe, sockfd, iov->iov_base, iov->iov_len, MSG_WAITALL); } else { - msg.msg_namelen = sizeof(struct sockaddr_in); - msg.msg_iov = iov; - msg.msg_iovlen = 1; - io_uring_prep_recvmsg(sqe, sockfd, &msg, MSG_WAITALL); + struct msghdr *msg = &rd->msg; + + memset(msg, 0, sizeof(*msg)); + msg->msg_namelen = sizeof(struct sockaddr_in); + msg->msg_iov = iov; + msg->msg_iovlen = 1; + io_uring_prep_recvmsg(sqe, sockfd, msg, MSG_WAITALL); } sqe->user_data = 2; @@ -101,11 +108,6 @@ err: return 1; } -struct recv_data { - pthread_mutex_t mutex; - int use_recvmsg; -}; - static void *recv_fn(void *data) { struct recv_data *rd = data; @@ -128,7 +130,7 @@ static void *recv_fn(void *data) goto err; } - ret = recv_prep(&ring, &iov, &sock, rd->use_recvmsg); + ret = recv_prep(&ring, &iov, &sock, rd); if (ret) { fprintf(stderr, "recv_prep failed: %d\n", ret); goto err; -- Ammar Faizi
Calling pthread_mutex_lock() twice with the same mutex in the same thread without unlocking it first is invalid. The intention behind this pattern was to wait for the recv_fn() thread to be ready. Use the pthread barrier instead. It is more straightforward and correct. Fixes: https://github.com/axboe/liburing/issues/855 Reported-by: Barnabás Pőcze <pobrn@protonmail.com> Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org> --- test/recv-msgall.c | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-) diff --git a/test/recv-msgall.c b/test/recv-msgall.c index f809834b2e427fc5..d1fcdb0d510423e7 100644 --- a/test/recv-msgall.c +++ b/test/recv-msgall.c @@ -19,7 +19,7 @@ #define HOST "127.0.0.1" static __be16 bind_port; struct recv_data { - pthread_mutex_t mutex; + pthread_barrier_t barrier; int use_recvmsg; struct msghdr msg; }; @@ -122,11 +122,11 @@ static void *recv_fn(void *data) ret = t_create_ring_params(1, &ring, &p); if (ret == T_SETUP_SKIP) { - pthread_mutex_unlock(&rd->mutex); + pthread_barrier_wait(&rd->barrier); ret = 0; goto err; } else if (ret < 0) { - pthread_mutex_unlock(&rd->mutex); + pthread_barrier_wait(&rd->barrier); goto err; } @@ -135,7 +135,7 @@ static void *recv_fn(void *data) fprintf(stderr, "recv_prep failed: %d\n", ret); goto err; } - pthread_mutex_unlock(&rd->mutex); + pthread_barrier_wait(&rd->barrier); ret = do_recv(&ring); close(sock); io_uring_queue_exit(&ring); @@ -219,28 +219,24 @@ err: static int test(int use_recvmsg) { - pthread_mutexattr_t attr; pthread_t recv_thread; struct recv_data rd; int ret; void *retval; - pthread_mutexattr_init(&attr); - pthread_mutexattr_setpshared(&attr, 1); - pthread_mutex_init(&rd.mutex, &attr); - pthread_mutex_lock(&rd.mutex); + pthread_barrier_init(&rd.barrier, NULL, 2); rd.use_recvmsg = use_recvmsg; ret = pthread_create(&recv_thread, NULL, recv_fn, &rd); if (ret) { fprintf(stderr, "Thread create failed: %d\n", ret); - pthread_mutex_unlock(&rd.mutex); return 1; } - pthread_mutex_lock(&rd.mutex); + pthread_barrier_wait(&rd.barrier); do_send(); pthread_join(recv_thread, &retval); + pthread_barrier_destroy(&rd.barrier); return (intptr_t)retval; } -- Ammar Faizi
On Wed, 10 May 2023 21:39:25 +0700, Ammar Faizi wrote:
> This is the follow up patchset for the recent issue found in
> recv-msgall.c. There are two patches in this series.
>
> 1. Fix undefined behavior in `recv_prep()`.
> The lifetime of `struct msghdr msg;` must be long enough until the CQE
> is generated because the recvmsg operation will write to that storage. I
> found this test segfault when compiling with -O0 optimization. This is
> undefined behavior and may behave randomly. Fix this by making the
> lifetime of `struct msghdr msg;` long enough.
>
> [...]
Applied, thanks!
[1/2] recv-msgall: Fix undefined behavior in `recv_prep()`
commit: 05c6317367cab6fd4b8cf38c68cea1563bf31c5f
[2/2] recv-msgall: Fix invalid mutex usage
commit: 09c3661278bebb8431fbc10ed213e42181e7cac7
Best regards,
--
Jens Axboe