firewire: cdev: reduce stack usage by ioctl_dispatch

Replace a hardcoded buffer size by a sizeof union {}.  This shrinks the
stack-allocated ioctl argument buffer from 256 to 40 bytes.  (This is
not much, but subsequent stack usage particularly by the queue_iso ioctl
handler adds up.)

The new form is also easier to keep up to date than a hardcoded size if
more ioctls are added.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

1 files changed, 17 insertions, 1 deletions

diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
index 1accfaf96c6f..e7290928a900 100644
--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -1299,7 +1299,23 @@ static int (* const ioctl_handlers[])(struct client *client, void *buffer) = {
 static int dispatch_ioctl(struct client *client,
                           unsigned int cmd, void __user *arg)
 {
-        char buffer[256];
+        char buffer[sizeof(union {
+                struct fw_cdev_get_info                 _00;
+                struct fw_cdev_send_request             _01;
+                struct fw_cdev_allocate                 _02;
+                struct fw_cdev_deallocate               _03;
+                struct fw_cdev_send_response            _04;
+                struct fw_cdev_initiate_bus_reset       _05;
+                struct fw_cdev_add_descriptor           _06;
+                struct fw_cdev_remove_descriptor        _07;
+                struct fw_cdev_create_iso_context       _08;
+                struct fw_cdev_queue_iso                _09;
+                struct fw_cdev_start_iso                _0a;
+                struct fw_cdev_stop_iso                 _0b;
+                struct fw_cdev_get_cycle_timer          _0c;
+                struct fw_cdev_allocate_iso_resource    _0d;
+                struct fw_cdev_send_stream_packet       _13;
+        })];
         int ret;
 
         if (_IOC_TYPE(cmd) != '#' ||