linux-kernel - Re: [PATCH v2 RESEND] PCI: fix reference leak in pci_alloc_child

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Message-ID: <46c252b0-880c-aca1-f6e5-c78ebe28a7a0@linux.intel.com>
Date: Fri, 24 Jan 2025 11:19:33 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Ma Ke <make24@...as.ac.cn>
cc: bhelgaas@...gle.com, yinghai@...nel.org, rafael.j.wysocki@...el.com, 
    akpm@...ux-foundation.org, linux-pci@...r.kernel.org, 
    LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org
Subject: Re: [PATCH v2 RESEND] PCI: fix reference leak in
 pci_alloc_child_bus()

On Sun, 19 Jan 2025, Ma Ke wrote:

> When device_register(&child->dev) failed, calling put_device() to
> explicitly release child->dev. Otherwise, it could cause double free
> problem.

While the code fix seem okay, this double free part in the problem 
description isn't. The reference is held w/o this fix so it's not getting 
freed at all, let alone freed twice.

> device_register() includes device_add(). As comment of device_add()
> says, 'if device_add() succeeds, you should call device_del() when you
> want to get rid of it. If device_add() has not succeeded, use only
> put_device() to drop the reference count'.
> 
> Found by code review.
> 
> Cc: stable@...r.kernel.org
> Fixes: 4f535093cf8f ("PCI: Put pci_dev in device tree as early as possible")
> Signed-off-by: Ma Ke <make24@...as.ac.cn>
> ---
> Changes in v2:
> - added the bug description about the comment of device_add();
> - fixed the patch as suggestions;
> - added Cc and Fixes table.
> ---
>  drivers/pci/probe.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 2e81ab0f5a25..ae12f92c6a9d 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1174,7 +1174,10 @@ static struct pci_bus *pci_alloc_child_bus(struct pci_bus *parent,
>  add_dev:
>  	pci_set_bus_msi_domain(child);
>  	ret = device_register(&child->dev);
> -	WARN_ON(ret < 0);
> +	if (WARN_ON(ret < 0)) {
> +		put_device(&child->dev);
> +		return NULL;
> +	}
>  
>  	pcibios_add_bus(child);
>  
> 

-- 
 i.