firmware loader: fix pending_fw_head list corruption

Got the following oops just before reboot:

Unable to handle kernel NULL pointer dereference at virtual address 00000000
[<8028d300>] (__list_del_entry+0x44/0xac)
[<802e3320>] (__fw_load_abort.part.13+0x1c/0x50)
[<802e337c>] (fw_shutdown_notify+0x28/0x50)
[<80034f80>] (notifier_call_chain.isra.1+0x5c/0x9c)
[<800350ec>] (__blocking_notifier_call_chain+0x44/0x58)
[<80035114>] (blocking_notifier_call_chain+0x14/0x18)
[<80035d64>] (kernel_restart_prepare+0x14/0x38)
[<80035d94>] (kernel_restart+0xc/0x50)

The following race condition triggers here:

  _request_firmware_load()
  device_create_file(...)
  kobject_uevent(...)
  (schedule)
                                       (resume)
                                       firmware_loading_store(1)
                                       firmware_loading_store(0)
                                       list_del_init(&buf->pending_list)
                                       (schedule)
  (resume)
  list_add(&buf->pending_list, &pending_fw_head);
  wait_for_completion(&buf->completion);

causing an oops later when walking pending_list after the firmware has
been released.

The proposed fix is to move the list_add() before sysfs attribute
creation.

Signed-off-by: Maxime Bizon <mbizon@freebox.fr>
Acked-by: Ming Lei <ming.lei@canonical.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 7 insertions, 4 deletions

diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index e4107d5f036b..10a4467c63f1 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -865,8 +865,15 @@ static int _request_firmware_load(struct firmware_priv *fw_priv, bool uevent,
                 goto err_del_dev;
         }
 
+        mutex_lock(&fw_lock);
+        list_add(&buf->pending_list, &pending_fw_head);
+        mutex_unlock(&fw_lock);
+
         retval = device_create_file(f_dev, &dev_attr_loading);
         if (retval) {
+                mutex_lock(&fw_lock);
+                list_del_init(&buf->pending_list);
+                mutex_unlock(&fw_lock);
                 dev_err(f_dev, "%s: device_create_file failed\n", __func__);
                 goto err_del_bin_attr;
         }
@@ -881,10 +888,6 @@ static int _request_firmware_load(struct firmware_priv *fw_priv, bool uevent,
                 kobject_uevent(&fw_priv->dev.kobj, KOBJ_ADD);
         }
 
-        mutex_lock(&fw_lock);
-        list_add(&buf->pending_list, &pending_fw_head);
-        mutex_unlock(&fw_lock);
-
         wait_for_completion(&buf->completion);
 
         cancel_delayed_work_sync(&fw_priv->timeout_work);