From 4ae2182b1e3407de369f8c5d799543b7db74221b Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Mon, 25 Jan 2016 10:08:00 -0600 Subject: [PATCH] PCI/AER: Flush workqueue on device remove to avoid use-after-free A Root Port's AER structure (rpc) contains a queue of events. aer_irq() enqueues AER status information and schedules aer_isr() to dequeue and process it. When we remove a device, aer_remove() waits for the queue to be empty, then frees the rpc struct. But aer_isr() references the rpc struct after dequeueing and possibly emptying the queue, which can cause a use-after-free error as in the following scenario with two threads, aer_isr() on the left and a concurrent aer_remove() on the right: Thread A Thread B -------- -------- aer_irq(): rpc->prod_idx++ aer_remove(): wait_event(rpc->prod_idx == rpc->cons_idx) # now blocked until queue becomes empty aer_isr(): # ... rpc->cons_idx++ # unblocked because queue is now empty ... kfree(rpc) mutex_unlock(&rpc->rpc_mutex) To prevent this problem, use flush_work() to wait until the last scheduled instance of aer_isr() has completed before freeing the rpc struct in aer_remove(). I reproduced this use-after-free by flashing a device FPGA and re-enumerating the bus to find the new device. With SLUB debug, this crashes with 0x6b bytes (POISON_FREE, the use-after-free magic number) in GPR25: pcieport 0000:00:00.0: AER: Multiple Corrected error received: id=0000 Unable to handle kernel paging request for data at address 0x27ef9e3e Workqueue: events aer_isr GPR24: dd6aa000 6b6b6b6b 605f8378 605f8360 d99b12c0 604fc674 606b1704 d99b12c0 NIP [602f5328] pci_walk_bus+0xd4/0x104 [bhelgaas: changelog, stable tag] Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Bjorn Helgaas CC: stable@vger.kernel.org --- drivers/pci/pcie/aer/aerdrv.c | 4 +--- drivers/pci/pcie/aer/aerdrv.h | 1 - drivers/pci/pcie/aer/aerdrv_core.c | 2 -- 3 files changed, 1 insertion(+), 6 deletions(-) diff --git a/drivers/pci/pcie/aer/aerdrv.c b/drivers/pci/pcie/aer/aerdrv.c index 0bf82a20a0fb..48d21e0edd56 100644 --- a/drivers/pci/pcie/aer/aerdrv.c +++ b/drivers/pci/pcie/aer/aerdrv.c @@ -262,7 +262,6 @@ static struct aer_rpc *aer_alloc_rpc(struct pcie_device *dev) rpc->rpd = dev; INIT_WORK(&rpc->dpc_handler, aer_isr); mutex_init(&rpc->rpc_mutex); - init_waitqueue_head(&rpc->wait_release); /* Use PCIe bus function to store rpc into PCIe device */ set_service_data(dev, rpc); @@ -285,8 +284,7 @@ static void aer_remove(struct pcie_device *dev) if (rpc->isr) free_irq(dev->irq, dev); - wait_event(rpc->wait_release, rpc->prod_idx == rpc->cons_idx); - + flush_work(&rpc->dpc_handler); aer_disable_rootport(rpc); kfree(rpc); set_service_data(dev, NULL); diff --git a/drivers/pci/pcie/aer/aerdrv.h b/drivers/pci/pcie/aer/aerdrv.h index 84420b7c9456..945c939a86c5 100644 --- a/drivers/pci/pcie/aer/aerdrv.h +++ b/drivers/pci/pcie/aer/aerdrv.h @@ -72,7 +72,6 @@ struct aer_rpc { * recovery on the same * root port hierarchy */ - wait_queue_head_t wait_release; }; struct aer_broadcast_data { diff --git a/drivers/pci/pcie/aer/aerdrv_core.c b/drivers/pci/pcie/aer/aerdrv_core.c index 712392504ed9..521e39c1b66d 100644 --- a/drivers/pci/pcie/aer/aerdrv_core.c +++ b/drivers/pci/pcie/aer/aerdrv_core.c @@ -811,8 +811,6 @@ void aer_isr(struct work_struct *work) while (get_e_source(rpc, &e_src)) aer_isr_one_error(p_device, &e_src); mutex_unlock(&rpc->rpc_mutex); - - wake_up(&rpc->wait_release); } /** -- 2.20.1