linux-kernel - Re: [PATCH 3/3] VMCI: Fix some error handling paths in vmci_guest_probe

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Date:   Fri, 11 Feb 2022 17:09:50 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     jhansen@...are.com, vdasa@...are.com, arnd@...db.de,
        gregkh@...uxfoundation.org, acking@...are.com, dtor@...are.com,
        pv-drivers@...are.com, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 3/3] VMCI: Fix some error handling paths in
 vmci_guest_probe_device()

On Thu, Feb 10, 2022 at 11:27:34PM +0100, Christophe JAILLET wrote:
> The 'err_remove_vmci_dev_g' error label is not at the right place.
> This could lead to un-released resource.
> 
> There is also a missing label. If pci_alloc_irq_vectors() fails, the
> previous vmci_event_subscribe() call must be undone.
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> Review with GREAT care.
> 
> This patch is a recent rebase of an old patch that has never been
> submitted.
> This function is huge and modifying its error handling path is error
> prone (at least for me).
> 
> The patch is compile-tested only.

There is still one bug.  Sorry if the line numbers are off.

drivers/misc/vmw_vmci/vmci_guest.c
   705                if (capabilities & VMCI_CAPS_NOTIFICATIONS) {
   706                        vmci_dev->notification_bitmap = dma_alloc_coherent(
                                                                  ^^^^^
Alloc

   707                                &pdev->dev, PAGE_SIZE, &vmci_dev->notification_base,
   708                                GFP_KERNEL);
   709                        if (!vmci_dev->notification_bitmap) {
   710                                dev_warn(&pdev->dev,
   711                                         "Unable to allocate notification bitmap\n");
   712                        } else {
   713                                memset(vmci_dev->notification_bitmap, 0, PAGE_SIZE);
   714                                caps_in_use |= VMCI_CAPS_NOTIFICATIONS;
   715                        }
   716                }
   717
   718                if (mmio_base != NULL) {
   719                        if (capabilities & VMCI_CAPS_DMA_DATAGRAM) {
   720                                caps_in_use |= VMCI_CAPS_DMA_DATAGRAM;
   721                        } else {
   722                                dev_err(&pdev->dev,
   723                                        "Missing capability: VMCI_CAPS_DMA_DATAGRAM\n");
   724                                error = -ENXIO;
   725                                goto err_free_data_buffers;

This should be goto err_free_notification_bitmap;

   726                        }
   727                }

On of the rules for error handling is that the unwind code should mirror
the allocation code but instead of that this code will have:

Alloc:
	if (capabilities & VMCI_CAPS_NOTIFICATIONS)
Free:
	if (vmci_dev->notification_bitmap)

It's the same if statement but you wouldn't really know it from just
looking at it so it's confusing.  Whatever...  But where this really
hurts is with:

Alloc:
	if (vmci_dev->exclusive_vectors) {
		error = request_irq(pci_irq_vector(pdev, 1), ...
Free:
	free_irq(pci_irq_vector(pdev, 1), vmci_dev);

No if statement.  It works because it's the last allocation but it's
confusing and fragile.

The other question I had was:

   882        err_remove_bitmap:
   883                if (vmci_dev->notification_bitmap) {
   884                        vmci_write_reg(vmci_dev, VMCI_CONTROL_RESET, VMCI_CONTROL_ADDR);
                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This doesn't mirror anything in the allocation code so who knows if its
done in the correct place/order.

   885                        dma_free_coherent(&pdev->dev, PAGE_SIZE,
   886                                          vmci_dev->notification_bitmap,
   887                                          vmci_dev->notification_base);
   888                }

regards,
dan carpenter