[PATCH 3/8] firewire: cdev: reduce stack usage by ioctl_dispatch

[Stefan Richter]

Shrink the stack-allocated ioctl argument buffer from 256 to 40 bytes.
This is the maximum of what we currently need for all ioctls.

Also, turn runtime checks of the buffer size into compile-time checks.
This involves a few more lines of code but they are all taken care of by
the compiler's dead code elimination, and this way the buffer size
should actually be a little easier to update when new ioctls are added.

Signed-off-by: Stefan Richter <stefanr@xxxxxxxxxxxxxxxxx>
---
 drivers/firewire/core-cdev.c |   41 ++++++++++++++++++++++++++---------
 1 file changed, 30 insertions(+), 11 deletions(-)

Index: linux-2.6.31/drivers/firewire/core-cdev.c
===================================================================
--- linux-2.6.31.orig/drivers/firewire/core-cdev.c
+++ linux-2.6.31/drivers/firewire/core-cdev.c
@@ -1299,28 +1299,47 @@ static int (* const ioctl_handlers[])(st
 static int dispatch_ioctl(struct client *client,
 			  unsigned int cmd, void __user *arg)
 {
-	char buffer[256];
+	char buffer[40];
 	int ret;
 
+#define check_ioctl_size(x) BUILD_BUG_ON(_IOC_SIZE(x) > sizeof(buffer))
+
+	check_ioctl_size(FW_CDEV_IOC_GET_INFO);
+	check_ioctl_size(FW_CDEV_IOC_SEND_REQUEST);
+	check_ioctl_size(FW_CDEV_IOC_ALLOCATE);
+	check_ioctl_size(FW_CDEV_IOC_DEALLOCATE);
+	check_ioctl_size(FW_CDEV_IOC_SEND_RESPONSE);
+	check_ioctl_size(FW_CDEV_IOC_INITIATE_BUS_RESET);
+	check_ioctl_size(FW_CDEV_IOC_ADD_DESCRIPTOR);
+	check_ioctl_size(FW_CDEV_IOC_REMOVE_DESCRIPTOR);
+	check_ioctl_size(FW_CDEV_IOC_CREATE_ISO_CONTEXT);
+	check_ioctl_size(FW_CDEV_IOC_QUEUE_ISO);
+	check_ioctl_size(FW_CDEV_IOC_START_ISO);
+	check_ioctl_size(FW_CDEV_IOC_STOP_ISO);
+	check_ioctl_size(FW_CDEV_IOC_GET_CYCLE_TIMER);
+	check_ioctl_size(FW_CDEV_IOC_ALLOCATE_ISO_RESOURCE);
+	check_ioctl_size(FW_CDEV_IOC_DEALLOCATE_ISO_RESOURCE);
+	check_ioctl_size(FW_CDEV_IOC_ALLOCATE_ISO_RESOURCE_ONCE);
+	check_ioctl_size(FW_CDEV_IOC_DEALLOCATE_ISO_RESOURCE_ONCE);
+	check_ioctl_size(FW_CDEV_IOC_GET_SPEED);
+	check_ioctl_size(FW_CDEV_IOC_SEND_BROADCAST_REQUEST);
+	check_ioctl_size(FW_CDEV_IOC_SEND_STREAM_PACKET);
+
 	if (_IOC_TYPE(cmd) != '#' ||
 	    _IOC_NR(cmd) >= ARRAY_SIZE(ioctl_handlers))
 		return -EINVAL;
 
-	if (_IOC_DIR(cmd) & _IOC_WRITE) {
-		if (_IOC_SIZE(cmd) > sizeof(buffer) ||
-		    copy_from_user(buffer, arg, _IOC_SIZE(cmd)))
-			return -EFAULT;
-	}
+	if (_IOC_DIR(cmd) & _IOC_WRITE &&
+	    copy_from_user(buffer, arg, _IOC_SIZE(cmd)))
+		return -EFAULT;
 
 	ret = ioctl_handlers[_IOC_NR(cmd)](client, buffer);
 	if (ret < 0)
 		return ret;
 
-	if (_IOC_DIR(cmd) & _IOC_READ) {
-		if (_IOC_SIZE(cmd) > sizeof(buffer) ||
-		    copy_to_user(arg, buffer, _IOC_SIZE(cmd)))
-			return -EFAULT;
-	}
+	if (_IOC_DIR(cmd) & _IOC_READ &&
+	    copy_to_user(arg, buffer, _IOC_SIZE(cmd)))
+		return -EFAULT;
 
 	return ret;
 }

-- 
Stefan Richter
-=====-==--= =-=- -=---
http://arcgraph.de/sr/

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