Re: [PATCH] PCI/MSI: Prevent UAF in error path

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Jan 19, 2022 at 06:54:52PM +0100, Thomas Gleixner wrote:
> When the core MSI allocation fails, then the PCI/MSI code uses an already
> freed MSI descriptor to unmask the MSI mask register in order to bring it back
> into reset state.
> 
> Remove MSI_FLAG_FREE_MSI_DESCS from the PCI/MSI irqdomain flags and let the
> PCI/MSI code free the MSI descriptors after usage.
> 
> Fixes: 0f62d941acf9 ("genirq/msi: Provide msi_domain_alloc/free_irqs_descs_locked()")
> Reported-by: Tong Zhang <ztong0001@gmail.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

What does "UAF" stand for?  Ah, "use after free" I guess?

Let me know if I should take this.  Otherwise I assume it'll go
whereever 0f62d941acf9 went.

> ---
>  drivers/pci/msi/irqdomain.c |    4 ++--
>  drivers/pci/msi/legacy.c    |    1 -
>  2 files changed, 2 insertions(+), 3 deletions(-)
> 
> --- a/drivers/pci/msi/irqdomain.c
> +++ b/drivers/pci/msi/irqdomain.c
> @@ -28,6 +28,7 @@ void pci_msi_teardown_msi_irqs(struct pc
>  		msi_domain_free_irqs_descs_locked(domain, &dev->dev);
>  	else
>  		pci_msi_legacy_teardown_msi_irqs(dev);
> +	msi_free_msi_descs(&dev->dev);
>  }
>  
>  /**
> @@ -171,8 +172,7 @@ struct irq_domain *pci_msi_create_irq_do
>  	if (info->flags & MSI_FLAG_USE_DEF_CHIP_OPS)
>  		pci_msi_domain_update_chip_ops(info);
>  
> -	info->flags |= MSI_FLAG_ACTIVATE_EARLY | MSI_FLAG_DEV_SYSFS |
> -		       MSI_FLAG_FREE_MSI_DESCS;
> +	info->flags |= MSI_FLAG_ACTIVATE_EARLY | MSI_FLAG_DEV_SYSFS;
>  	if (IS_ENABLED(CONFIG_GENERIC_IRQ_RESERVATION_MODE))
>  		info->flags |= MSI_FLAG_MUST_REACTIVATE;
>  
> --- a/drivers/pci/msi/legacy.c
> +++ b/drivers/pci/msi/legacy.c
> @@ -77,5 +77,4 @@ void pci_msi_legacy_teardown_msi_irqs(st
>  {
>  	msi_device_destroy_sysfs(&dev->dev);
>  	arch_teardown_msi_irqs(dev);
> -	msi_free_msi_descs(&dev->dev);
>  }