1 files changed, 20 insertions, 9 deletions

diff --git a/drivers/firewire/fw-cdev.c b/drivers/firewire/fw-cdev.c
index bc81d6fcd2f..2e6d5848d21 100644
--- a/drivers/firewire/fw-cdev.c
+++ b/drivers/firewire/fw-cdev.c
@@ -369,22 +369,33 @@ complete_transaction(struct fw_card *card, int rcode,
         struct response *response = data;
         struct client *client = response->client;
         unsigned long flags;
+        struct fw_cdev_event_response *r = &response->response;
 
-        if (length < response->response.length)
-                response->response.length = length;
+        if (length < r->length)
+                r->length = length;
         if (rcode == RCODE_COMPLETE)
-                memcpy(response->response.data, payload,
-                       response->response.length);
+                memcpy(r->data, payload, r->length);
 
         spin_lock_irqsave(&client->lock, flags);
         list_del(&response->resource.link);
         spin_unlock_irqrestore(&client->lock, flags);
 
-        response->response.type   = FW_CDEV_EVENT_RESPONSE;
-        response->response.rcode  = rcode;
-        queue_event(client, &response->event, &response->response,
-                    sizeof(response->response) + response->response.length,
-                    NULL, 0);
+        r->type   = FW_CDEV_EVENT_RESPONSE;
+        r->rcode  = rcode;
+
+        /*
+         * In the case that sizeof(*r) doesn't align with the position of the
+         * data, and the read is short, preserve an extra copy of the data
+         * to stay compatible with a pre-2.6.27 bug.  Since the bug is harmless
+         * for short reads and some apps depended on it, this is both safe
+         * and prudent for compatibility.
+         */
+        if (r->length <= sizeof(*r) - offsetof(typeof(*r), data))
+                queue_event(client, &response->event, r, sizeof(*r),
+                            r->data, r->length);
+        else
+                queue_event(client, &response->event, r, sizeof(*r) + r->length,
+                            NULL, 0);
 }
 
 static int ioctl_send_request(struct client *client, void *buffer)