osmo_io: Reject writing messages with length of 0

io_uring will reject to transmit messages with length of 0.

Change-Id: I94be5ec7344d92157f7853c6c0ddf7007513ba8e
Related: OS#5751
diff --git a/src/core/osmo_io.c b/src/core/osmo_io.c
index 5d25f66..472edf9 100644
--- a/src/core/osmo_io.c
+++ b/src/core/osmo_io.c
@@ -409,6 +409,11 @@
 {
 	int rc;
 
+	if (OSMO_UNLIKELY(msgb_length(msg) == 0)) {
+		LOGPIO(iofd, LOGL_ERROR, "Length is 0, rejecting msgb.\n");
+		return -EINVAL;
+	}
+
 	OSMO_ASSERT(iofd->mode == OSMO_IO_FD_MODE_READ_WRITE);
 	if (OSMO_UNLIKELY(!iofd->io_ops.write_cb)) {
 		LOGPIO(iofd, LOGL_ERROR, "write_cb not set, Rejecting msgb\n");
@@ -451,6 +456,11 @@
 {
 	int rc;
 
+	if (OSMO_UNLIKELY(msgb_length(msg) == 0)) {
+		LOGPIO(iofd, LOGL_ERROR, "Length is 0, rejecting msgb.\n");
+		return -EINVAL;
+	}
+
 	OSMO_ASSERT(iofd->mode == OSMO_IO_FD_MODE_RECVFROM_SENDTO);
 	if (OSMO_UNLIKELY(!iofd->io_ops.sendto_cb)) {
 		LOGPIO(iofd, LOGL_ERROR, "sendto_cb not set, Rejecting msgb\n");
@@ -499,6 +509,11 @@
 	int rc;
 	struct iofd_msghdr *msghdr;
 
+	if (OSMO_UNLIKELY(msgb_length(msg) == 0)) {
+		LOGPIO(iofd, LOGL_ERROR, "Length is 0, rejecting msgb.\n");
+		return -EINVAL;
+	}
+
 	OSMO_ASSERT(iofd->mode == OSMO_IO_FD_MODE_RECVMSG_SENDMSG);
 	if (OSMO_UNLIKELY(!iofd->io_ops.sendmsg_cb)) {
 		LOGPIO(iofd, LOGL_ERROR, "sendmsg_cb not set, Rejecting msgb\n");