scsi: iscsi: iscsi_tcp: Fix null-ptr-deref while calling getpeername()

Fix a NULL pointer crash that occurs when we are freeing the socket at the
same time we access it via sysfs.

The problem is that:

 1. iscsi_sw_tcp_conn_get_param() and iscsi_sw_tcp_host_get_param() take
    the frwd_lock and do sock_hold() then drop the frwd_lock. sock_hold()
    does a get on the "struct sock".

 2. iscsi_sw_tcp_release_conn() does sockfd_put() which does the last put
    on the "struct socket" and that does __sock_release() which sets the
    sock->ops to NULL.

 3. iscsi_sw_tcp_conn_get_param() and iscsi_sw_tcp_host_get_param() then
    call kernel_getpeername() which accesses the NULL sock->ops.

Above we do a get on the "struct sock", but we needed a get on the "struct
socket". Originally, we just held the frwd_lock the entire time but in
commit bcf3a2953d ("scsi: iscsi: iscsi_tcp: Avoid holding spinlock while
calling getpeername()") we switched to refcount based because the network
layer changed and started taking a mutex in that path, so we could no
longer hold the frwd_lock.

Instead of trying to maintain multiple refcounts, this just has us use a
mutex for accessing the socket in the interface code paths.

Link: https://lore.kernel.org/r/20220907221700.10302-1-michael.christie@oracle.com
Fixes: bcf3a2953d ("scsi: iscsi: iscsi_tcp: Avoid holding spinlock while calling getpeername()")
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/iscsi_tcp.c

@@ -595,6 +595,8 @@ iscsi_sw_tcp_conn_create(struct iscsi_cls_session *cls_session,
 	INIT_WORK(&conn->recvwork, iscsi_sw_tcp_recv_data_work);
 	tcp_sw_conn->queue_recv = iscsi_recv_from_iscsi_q;
 
+	mutex_init(&tcp_sw_conn->sock_lock);
+
 	tfm = crypto_alloc_ahash("crc32c", 0, CRYPTO_ALG_ASYNC);
 	if (IS_ERR(tfm))
 		goto free_conn;
@@ -629,11 +631,15 @@ free_conn:
 
 static void iscsi_sw_tcp_release_conn(struct iscsi_conn *conn)
 {
-	struct iscsi_session *session = conn->session;
 	struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
 	struct iscsi_sw_tcp_conn *tcp_sw_conn = tcp_conn->dd_data;
 	struct socket *sock = tcp_sw_conn->sock;
 
+	/*
+	 * The iscsi transport class will make sure we are not called in
+	 * parallel with start, stop, bind and destroys. However, this can be
+	 * called twice if userspace does a stop then a destroy.
+	 */
 	if (!sock)
 		return;
 
@@ -649,9 +655,9 @@ static void iscsi_sw_tcp_release_conn(struct iscsi_conn *conn)
 
 	iscsi_suspend_rx(conn);
 
-	spin_lock_bh(&session->frwd_lock);
+	mutex_lock(&tcp_sw_conn->sock_lock);
 	tcp_sw_conn->sock = NULL;
-	spin_unlock_bh(&session->frwd_lock);
+	mutex_unlock(&tcp_sw_conn->sock_lock);
 	sockfd_put(sock);
 }
 
@@ -703,7 +709,6 @@ iscsi_sw_tcp_conn_bind(struct iscsi_cls_session *cls_session,
 		       struct iscsi_cls_conn *cls_conn, uint64_t transport_eph,
 		       int is_leading)
 {
-	struct iscsi_session *session = cls_session->dd_data;
 	struct iscsi_conn *conn = cls_conn->dd_data;
 	struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
 	struct iscsi_sw_tcp_conn *tcp_sw_conn = tcp_conn->dd_data;
@@ -723,10 +728,10 @@ iscsi_sw_tcp_conn_bind(struct iscsi_cls_session *cls_session,
 	if (err)
 		goto free_socket;
 
-	spin_lock_bh(&session->frwd_lock);
+	mutex_lock(&tcp_sw_conn->sock_lock);
 	/* bind iSCSI connection and socket */
 	tcp_sw_conn->sock = sock;
-	spin_unlock_bh(&session->frwd_lock);
+	mutex_unlock(&tcp_sw_conn->sock_lock);
 
 	/* setup Socket parameters */
 	sk = sock->sk;
@@ -763,8 +768,15 @@ static int iscsi_sw_tcp_conn_set_param(struct iscsi_cls_conn *cls_conn,
 		break;
 	case ISCSI_PARAM_DATADGST_EN:
 		iscsi_set_param(cls_conn, param, buf, buflen);
+
+		mutex_lock(&tcp_sw_conn->sock_lock);
+		if (!tcp_sw_conn->sock) {
+			mutex_unlock(&tcp_sw_conn->sock_lock);
+			return -ENOTCONN;
+		}
 		tcp_sw_conn->sendpage = conn->datadgst_en ?
 			sock_no_sendpage : tcp_sw_conn->sock->ops->sendpage;
+		mutex_unlock(&tcp_sw_conn->sock_lock);
 		break;
 	case ISCSI_PARAM_MAX_R2T:
 		return iscsi_tcp_set_max_r2t(conn, buf);
@@ -779,8 +791,8 @@ static int iscsi_sw_tcp_conn_get_param(struct iscsi_cls_conn *cls_conn,
 				       enum iscsi_param param, char *buf)
 {
 	struct iscsi_conn *conn = cls_conn->dd_data;
-	struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
+	struct iscsi_sw_tcp_conn *tcp_sw_conn;
-	struct iscsi_sw_tcp_conn *tcp_sw_conn = tcp_conn->dd_data;
+	struct iscsi_tcp_conn *tcp_conn;
 	struct sockaddr_in6 addr;
 	struct socket *sock;
 	int rc;
@@ -790,21 +802,36 @@ static int iscsi_sw_tcp_conn_get_param(struct iscsi_cls_conn *cls_conn,
 	case ISCSI_PARAM_CONN_ADDRESS:
 	case ISCSI_PARAM_LOCAL_PORT:
 		spin_lock_bh(&conn->session->frwd_lock);
-		if (!tcp_sw_conn || !tcp_sw_conn->sock) {
+		if (!conn->session->leadconn) {
 			spin_unlock_bh(&conn->session->frwd_lock);
 			return -ENOTCONN;
 		}
-		sock = tcp_sw_conn->sock;
+		/*
-		sock_hold(sock->sk);
+		 * The conn has been setup and bound, so just grab a ref
+		 * incase a destroy runs while we are in the net layer.
+		 */
+		iscsi_get_conn(conn->cls_conn);
 		spin_unlock_bh(&conn->session->frwd_lock);
 
+		tcp_conn = conn->dd_data;
+		tcp_sw_conn = tcp_conn->dd_data;
+
+		mutex_lock(&tcp_sw_conn->sock_lock);
+		sock = tcp_sw_conn->sock;
+		if (!sock) {
+			rc = -ENOTCONN;
+			goto sock_unlock;
+		}
+
 		if (param == ISCSI_PARAM_LOCAL_PORT)
 			rc = kernel_getsockname(sock,
 						(struct sockaddr *)&addr);
 		else
 			rc = kernel_getpeername(sock,
 						(struct sockaddr *)&addr);
-		sock_put(sock->sk);
+sock_unlock:
+		mutex_unlock(&tcp_sw_conn->sock_lock);
+		iscsi_put_conn(conn->cls_conn);
 		if (rc < 0)
 			return rc;
 
@@ -842,17 +869,21 @@ static int iscsi_sw_tcp_host_get_param(struct Scsi_Host *shost,
 		}
 		tcp_conn = conn->dd_data;
 		tcp_sw_conn = tcp_conn->dd_data;
-		sock = tcp_sw_conn->sock;
+		/*
-		if (!sock) {
+		 * The conn has been setup and bound, so just grab a ref
-			spin_unlock_bh(&session->frwd_lock);
+		 * incase a destroy runs while we are in the net layer.
-			return -ENOTCONN;
+		 */
-		}
+		iscsi_get_conn(conn->cls_conn);
-		sock_hold(sock->sk);
 		spin_unlock_bh(&session->frwd_lock);
 
-		rc = kernel_getsockname(sock,
+		mutex_lock(&tcp_sw_conn->sock_lock);
-					(struct sockaddr *)&addr);
+		sock = tcp_sw_conn->sock;
-		sock_put(sock->sk);
+		if (!sock)
+			rc = -ENOTCONN;
+		else
+			rc = kernel_getsockname(sock, (struct sockaddr *)&addr);
+		mutex_unlock(&tcp_sw_conn->sock_lock);
+		iscsi_put_conn(conn->cls_conn);
 		if (rc < 0)
 			return rc;
 

drivers/scsi/iscsi_tcp.h

@@ -28,6 +28,9 @@ struct iscsi_sw_tcp_send {
 
 struct iscsi_sw_tcp_conn {
 	struct socket		*sock;
+	/* Taken when accessing the sock from the netlink/sysfs interface */
+	struct mutex		sock_lock;
+
 	struct work_struct	recvwork;
 	bool			queue_recv;