linux-kernel - Re: [PATCH -next 2/3] PCI: fix possible memory leak in error case in pci_register_host

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Message-ID: <20220826223810.GA2961041@bhelgaas>
Date:   Fri, 26 Aug 2022 17:38:10 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Yang Yingliang <yangyingliang@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        bhelgaas@...gle.com, Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH -next 2/3] PCI: fix possible memory leak in error case in
 pci_register_host_bridge()

[+cc Arnd, Rob]

On Thu, Aug 25, 2022 at 08:27:52PM +0800, Yang Yingliang wrote:
> If device_register() fails in pci_register_host_bridge(), the refcount
> of bus device is leaked, so device name that set by dev_set_name() can
> not be freed. Fix this by calling put_device() when device_register()
> fails, so the device name will be freed in kobject_cleanup().
>
> Fixes: 37d6a0a6f470 ("PCI: Add pci_register_host_bridge() interface")
> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
> ---
>  drivers/pci/probe.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index e500eb9d6468..292d9da146ce 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -948,8 +948,17 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>  	name = dev_name(&bus->dev);
>  
>  	err = device_register(&bus->dev);
> -	if (err)
> -		goto unregister;
> +	if (err) {
> +		/*
> +		 * release_pcibus_dev() will decrease the refcount of bridge
> +		 * device and free the memory of bus.
> +		 * The memory of bus device name will be freed when the refcount
> +		 * get to zero.
> +		 */
> +		put_device(&bus->dev);
> +		device_unregister(&bridge->dev);
> +		return err;
> +	}

Calling put_device(X) after device_register(X) returns failure doesn't
need explanation because that's the standard pattern.  I think that
was just missing before.

In this error case, we previously did called put_device() for the
*bridge* instead of the bus.  That was likely a typo and seems like
the important thing here.

>  	pcibios_add_bus(bus);
>  
> @@ -1025,10 +1034,6 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>  
>  	return 0;
>  
> -unregister:
> -	put_device(&bridge->dev);
> -	device_unregister(&bridge->dev);
> -
>  free:
>  	kfree(bus);
>  	return err;
> -- 
> 2.25.1
>