Re: [PATCH] PCI: pciehp: Differentiate between surprise and safe removal

[Lukas Wunner <lukas@wunner.de>]

[cc += Thomas Tai]

On Thu, Aug 02, 2018 at 10:46:57AM +0200, Lukas Wunner wrote:
> On Thu, Aug 02, 2018 at 12:59:18PM +0530, gokul cg wrote:
> > I am suspecting a possible race condition in the kernel between PCI driver
> > and AER handling.
> 
> The solution is to acquire a ref on each device in add_error_device().
> Then release the ref aer_process_err_devices() by calling pci_dev_put().

So in case it wasn't clear, the below is what I had in mind.
Completely untested though.  Does this work for you?

For v3.10 compatibility, cherry-pick 89ee9f768003 (or alternatively
cherry-pick 8496e85c20e7 and replace pci_dev_is_disconnected(dev)
with !pci_device_is_present(dev)).

-- >8 --
Subject: [PATCH] PCI/AER: Fix use-after-free on surprise removal

The work item to consume errors, aer_isr(), walks the hierarchy using
pci_walk_bus() and stores a pointer to PCI devices which reported an
error in an array.  As long as pci_walk_bus() runs, those pointers are
valid because pci_bus_sem is held.  But once pci_walk_bus() finishes,
nothing prevents the pointers from becoming invalid, e.g. through
unplugging of the PCI devices.  The unprotected pointers are then
dereferenced in aer_process_err_devices(), which may oops:

  #5  general_protection at ffffffff8176cdf2
      [exception RIP: pci_bus_read_config_dword+100]
  #6  pci_find_next_ext_capability at ffffffff81345d7b
  #7  pci_find_ext_capability at ffffffff81347225
  #8  get_device_error_info at ffffffff81356c4d
  #9  aer_isr at ffffffff81357a38

Fix by holding a ref on the devices until they have been processed.
Skip processing of unplugged devices.

Reported-by: gokul cg <gokuljnpr@gmail.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
---
 drivers/pci/pcie/aer.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
index a2e8838..937592e 100644
--- a/drivers/pci/pcie/aer.c
+++ b/drivers/pci/pcie/aer.c
@@ -657,7 +657,7 @@ void cper_print_aer(struct pci_dev *dev, int aer_severity,
 static int add_error_device(struct aer_err_info *e_info, struct pci_dev *dev)
 {
 	if (e_info->error_dev_num < AER_MAX_MULTI_ERR_DEVICES) {
-		e_info->dev[e_info->error_dev_num] = dev;
+		e_info->dev[e_info->error_dev_num] = pci_dev_get(dev);
 		e_info->error_dev_num++;
 		return 0;
 	}
@@ -898,6 +898,9 @@ static int get_device_error_info(struct pci_dev *dev, struct aer_err_info *info)
 	if (!pos)
 		return 0;
 
+	if (pci_dev_is_disconnected(dev))
+		return 0;
+
 	if (info->severity == AER_CORRECTABLE) {
 		pci_read_config_dword(dev, pos + PCI_ERR_COR_STATUS,
 			&info->status);
@@ -948,6 +951,7 @@ static inline void aer_process_err_devices(struct aer_err_info *e_info)
 	for (i = 0; i < e_info->error_dev_num && e_info->dev[i]; i++) {
 		if (get_device_error_info(e_info->dev[i], e_info))
 			handle_error_source(e_info->dev[i], e_info);
+		pci_dev_put(e_info->dev[i]);
 	}
 }
 
-- 
2.18.0