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PCI/AER: Flush workqueue on device remove to avoid use-after-free

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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 <bigeasy@linutronix.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: stable@vger.kernel.org
This commit is contained in:
Sebastian Andrzej Siewior 2016-01-25 10:08:00 -06:00 committed by Bjorn Helgaas
parent 92e963f50f
commit 4ae2182b1e
3 changed files with 1 additions and 6 deletions
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4
drivers/pci/pcie/aer/aerdrv.c
View File

@ -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);

1
drivers/pci/pcie/aer/aerdrv.h
View File

@ -72,7 +72,6 @@ struct aer_rpc {
* recovery on the same
* root port hierarchy
*/
wait_queue_head_t wait_release;
};
struct aer_broadcast_data {

2
drivers/pci/pcie/aer/aerdrv_core.c
View File

@ -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);
}
/**