firewire: cdev: fix user memory corruption (i386 userland on amd64 kernel)

Fix two bugs of the /dev/fw* character device concerning the FW_CDEV_IOC_GET_INFO ioctl with nonzero fw_cdev_get_info.bus_reset. (Practically all /dev/fw* clients issue this ioctl right after opening the device.)

Both bugs are caused by sizeof(struct fw_cdev_event_bus_reset) being 36 without natural alignment and 40 with natural alignment.

1) Memory corruption, affecting i386 userland on amd64 kernel:
Userland reserves a 36 bytes large buffer, kernel writes 40 bytes. This has been first found and reported against libraw1394 if compiled with gcc 4.7 which happens to order libraw1394's stack such that the bug became visible as data corruption.

2) Information leak, affecting all kernel architectures except i386:
4 bytes of random kernel stack data were leaked to userspace.

Hence limit the respective copy_to_user() to the 32-bit aligned size of struct fw_cdev_event_bus_reset.

---
 drivers/firewire/core-cdev.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -473,8 +473,8 @@ static int ioctl_get_info(struct client
 	client->bus_reset_closure = a->bus_reset_closure;
 	if (a->bus_reset != 0) {
 		fill_bus_reset_event(&bus_reset, client);
-		ret = copy_to_user(u64_to_uptr(a->bus_reset),
-				   &bus_reset, sizeof(bus_reset));
+		/* unaligned size of bus_reset is 36 bytes */
+		ret = copy_to_user(u64_to_uptr(a->bus_reset), &bus_reset, 36);
 	}
 	if (ret == 0 && list_empty(&client->link))
 		list_add_tail(&client->link, &client->device->client_list);

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