HID: protect hid_debug_list

Accesses to hid_device->hid_debug_list are not serialized properly, which
could result in SMP concurrency issues when HID debugfs events are accessesed
by multiple userspace processess.

Serialize all the list operations by a mutex.

Spotted by Al Viro.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>

2 files changed, 7 insertions, 0 deletions

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index f86dd9708ca5..e7765ede339e 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -2319,6 +2319,7 @@ struct hid_device *hid_allocate_device(void)
 
         init_waitqueue_head(&hdev->debug_wait);
         INIT_LIST_HEAD(&hdev->debug_list);
+        mutex_init(&hdev->debug_list_lock);
         sema_init(&hdev->driver_lock, 1);
 
         return hdev;
diff --git a/drivers/hid/hid-debug.c b/drivers/hid/hid-debug.c
index 094cbcfe1e1a..7e56cb3855e3 100644
--- a/drivers/hid/hid-debug.c
+++ b/drivers/hid/hid-debug.c
@@ -580,12 +580,14 @@ void hid_debug_event(struct hid_device *hdev, char *buf)
         int i;
         struct hid_debug_list *list;
 
+        mutex_lock(&hdev->debug_list_lock);
         list_for_each_entry(list, &hdev->debug_list, node) {
                 for (i = 0; i < strlen(buf); i++)
                         list->hid_debug_buf[(list->tail + i) % HID_DEBUG_BUFSIZE] =
                                 buf[i];
                 list->tail = (list->tail + i) % HID_DEBUG_BUFSIZE;
         }
+        mutex_unlock(&hdev->debug_list_lock);
 
         wake_up_interruptible(&hdev->debug_wait);
 }
@@ -990,7 +992,9 @@ static int hid_debug_events_open(struct inode *inode, struct file *file)
         file->private_data = list;
         mutex_init(&list->read_mutex);
 
+        mutex_lock(&list->hdev->debug_list_lock);
         list_add_tail(&list->node, &list->hdev->debug_list);
+        mutex_unlock(&list->hdev->debug_list_lock);
 
 out:
         return err;
@@ -1085,7 +1089,9 @@ static int hid_debug_events_release(struct inode *inode, struct file *file)
 {
         struct hid_debug_list *list = file->private_data;
 
+        mutex_lock(&list->hdev->debug_list_lock);
         list_del(&list->node);
+        mutex_unlock(&list->hdev->debug_list_lock);
         kfree(list->hid_debug_buf);
         kfree(list);