3.16.62-rc1 review patch. If anyone has any objections, please let me know.
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From: Lukas Wunner lukas@wunner.de
commit 281e878eab191cce4259abbbf1a0322e3adae02c upstream.
When pciehp is unbound (e.g. on unplug of a Thunderbolt device), the hotplug_slot struct is deregistered and thus freed before freeing the IRQ. The IRQ handler and the work items it schedules print the slot name referenced from the freed structure in various informational and debug log messages, each time resulting in a quadruple dereference of freed pointers (hotplug_slot -> pci_slot -> kobject -> name).
At best the slot name is logged as "(null)", at worst kernel memory is exposed in logs or the driver crashes:
pciehp 0000:10:00.0:pcie204: Slot((null)): Card not present
An attacker may provoke the bug by unplugging multiple devices on a Thunderbolt daisy chain at once. Unplugging can also be simulated by powering down slots via sysfs. The bug is particularly easy to trigger in poll mode.
It has been present since the driver's introduction in 2004: https://git.kernel.org/tglx/history/c/c16b4b14d980
Fix by rearranging teardown such that the IRQ is freed first. Run the work items queued by the IRQ handler to completion before freeing the hotplug_slot struct by draining the work queue from the ->release_slot callback which is invoked by pci_hp_deregister().
Signed-off-by: Lukas Wunner lukas@wunner.de Signed-off-by: Bjorn Helgaas bhelgaas@google.com [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/drivers/pci/hotplug/pciehp.h +++ b/drivers/pci/hotplug/pciehp.h @@ -141,6 +141,7 @@ int pciehp_unconfigure_device(struct slo void pciehp_queue_pushbutton_work(struct work_struct *work); struct controller *pcie_init(struct pcie_device *dev); int pcie_init_notification(struct controller *ctrl); +void pcie_shutdown_notification(struct controller *ctrl); int pciehp_enable_slot(struct slot *p_slot); int pciehp_disable_slot(struct slot *p_slot); void pcie_reenable_notification(struct controller *ctrl); --- a/drivers/pci/hotplug/pciehp_core.c +++ b/drivers/pci/hotplug/pciehp_core.c @@ -82,6 +82,10 @@ static void release_slot(struct hotplug_ ctrl_dbg(slot->ctrl, "%s: physical_slot = %s\n", __func__, hotplug_slot_name(hotplug_slot));
+ /* queued work needs hotplug_slot name */ + cancel_delayed_work(&slot->work); + drain_workqueue(slot->wq); + kfree(hotplug_slot->ops); kfree(hotplug_slot->info); kfree(hotplug_slot); @@ -313,6 +317,7 @@ static void pciehp_remove(struct pcie_de { struct controller *ctrl = get_service_data(dev);
+ pcie_shutdown_notification(ctrl); cleanup_slot(ctrl); pciehp_release_ctrl(ctrl); } --- a/drivers/pci/hotplug/pciehp_hpc.c +++ b/drivers/pci/hotplug/pciehp_hpc.c @@ -687,7 +687,7 @@ int pcie_init_notification(struct contro return 0; }
-static void pcie_shutdown_notification(struct controller *ctrl) +void pcie_shutdown_notification(struct controller *ctrl) { if (ctrl->notification_enabled) { pcie_disable_notification(ctrl); @@ -722,7 +722,7 @@ abort: static void pcie_cleanup_slot(struct controller *ctrl) { struct slot *slot = ctrl->slot; - cancel_delayed_work(&slot->work); + destroy_workqueue(slot->wq); kfree(slot); } @@ -846,7 +846,6 @@ abort:
void pciehp_release_ctrl(struct controller *ctrl) { - pcie_shutdown_notification(ctrl); pcie_cleanup_slot(ctrl); kfree(ctrl); }