[PATCH liburing v1 1/2] recv-msgall: Fix undefined behavior in `recv_prep()`

[Ammar Faizi <ammarfaizi2@gnuweeb.org>]

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