linux-kernel - Re: [PATCH] PCI: Fix NULL dereference in SR-IOV VF creation error path

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Message-ID: <20250227224547.GA22604@bhelgaas>
Date: Thu, 27 Feb 2025 16:45:47 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Shay Drory <shayd@...dia.com>
Cc: bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, Keith Busch <kbusch@...nel.org>,
	Leon Romanovsky <leonro@...dia.com>
Subject: Re: [PATCH] PCI: Fix NULL dereference in SR-IOV VF creation error
 path

On Sun, Feb 16, 2025 at 10:32:54AM +0200, Shay Drory wrote:
> Add proper cleanup when virtfn setup fails to prevent NULL pointer
> dereference during device removal. The kernel oops[1] occurred due to
> Incorrect error handling flow when pci_setup_device() fails.
> 
> Fix it by properly cleaning up virtfn resources when pci_setup_device()
> fails, instead of invoking pci_stop_and_remove_bus_device().
> This prevents accessing partially initialized virtfn devices during
> removal.

> Fixes: e3f30d563a38 ("PCI: Make pci_destroy_dev() concurrent safe")

It's not obvious to me how e3f30d563a38 is related.  Can you elucidate
the connection?

> CC: Keith Busch <kbusch@...nel.org>
> Reviewed-by: Leon Romanovsky <leonro@...dia.com>
> Signed-off-by: Shay Drory <shayd@...dia.com>
> ---
>  drivers/pci/iov.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index 9e4770cdd4d5..3dfcbf10e127 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c
> @@ -314,8 +314,11 @@ int pci_iov_add_virtfn(struct pci_dev *dev, int id)
>  		pci_read_vf_config_common(virtfn);
>  
>  	rc = pci_setup_device(virtfn);
> -	if (rc)
> +	if (rc) {
> +		pci_bus_put(virtfn->bus);
> +		kfree(virtfn);
>  		goto failed1;
> +	}

Thanks for the fix.  The mix of error recovery styles (cleanup here at
the point of falure vs. goto different cleanup steps at the end) makes
this kind of hard to understand.

I see that this cleanup is similar to what's done in
pci_scan_device(), which does help.  Did you consider making a helper
here with structure similar to pci_scan_device(), e.g., a
pci_iov_scan_device()?  I wonder if that could make the error handling
here simpler?

>  	virtfn->dev.parent = dev->dev.parent;
>  	virtfn->multifunction = 0;
> @@ -336,14 +339,15 @@ int pci_iov_add_virtfn(struct pci_dev *dev, int id)
>  	pci_device_add(virtfn, virtfn->bus);
>  	rc = pci_iov_sysfs_link(dev, virtfn, id);
>  	if (rc)
> -		goto failed1;
> +		goto failed2;
>  
>  	pci_bus_add_device(virtfn);
>  
>  	return 0;
>  
> -failed1:
> +failed2:
>  	pci_stop_and_remove_bus_device(virtfn);
> +failed1:
>  	pci_dev_put(dev);
>  failed0:
>  	virtfn_remove_bus(dev->bus, bus);
> -- 
> 2.38.1
>