9p: fix multiple NULL-pointer-dereferences

Added checks to prevent GPFs from raising.

Link: http://lkml.kernel.org/r/20180727110558.5479-1-tomasbortoli@gmail.com
Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
Reported-by: syzbot+1a262da37d3bead15c39@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>

net/9p/trans_fd.c

@@ -945,7 +945,7 @@ p9_fd_create_tcp(struct p9_client *client, const char *addr, char *args)
 	if (err < 0)
 		return err;
 
-	if (valid_ipaddr4(addr) < 0)
+	if (addr == NULL || valid_ipaddr4(addr) < 0)
 		return -EINVAL;
 
 	csocket = NULL;
@@ -995,6 +995,9 @@ p9_fd_create_unix(struct p9_client *client, const char *addr, char *args)
 
 	csocket = NULL;
 
+	if (addr == NULL)
+		return -EINVAL;
+
 	if (strlen(addr) >= UNIX_PATH_MAX) {
 		pr_err("%s (%d): address too long: %s\n",
 		       __func__, task_pid_nr(current), addr);

net/9p/trans_rdma.c

@@ -645,6 +645,9 @@ rdma_create_trans(struct p9_client *client, const char *addr, char *args)
 	struct rdma_conn_param conn_param;
 	struct ib_qp_init_attr qp_attr;
 
+	if (addr == NULL)
+		return -EINVAL;
+
 	/* Parse the transport specific mount options */
 	err = parse_opts(args, &opts);
 	if (err < 0)

net/9p/trans_virtio.c

@@ -654,6 +654,9 @@ p9_virtio_create(struct p9_client *client, const char *devname, char *args)
 	int ret = -ENOENT;
 	int found = 0;
 
+	if (devname == NULL)
+		return -EINVAL;
+
 	mutex_lock(&virtio_9p_lock);
 	list_for_each_entry(chan, &virtio_chan_list, chan_list) {
 		if (!strncmp(devname, chan->tag, chan->tag_len) &&

net/9p/trans_xen.c

@@ -94,6 +94,9 @@ static int p9_xen_create(struct p9_client *client, const char *addr, char *args)
 {
 	struct xen_9pfs_front_priv *priv;
 
+	if (addr == NULL)
+		return -EINVAL;
+
 	read_lock(&xen_9pfs_lock);
 	list_for_each_entry(priv, &xen_9pfs_devs, list) {
 		if (!strcmp(priv->tag, addr)) {