linux-kernel - Re: [PATCH] PCI/sysfs: Fix double free in error path

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Message-ID: <20221109230712.GA580188@bhelgaas>
Date:   Wed, 9 Nov 2022 17:07:12 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sascha Hauer <s.hauer@...gutronix.de>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>, stable@...r.kernel.org,
        Sergey Miroshnichenko <s.miroshnichenko@...ro.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Krzysztof Wilczyński <kw@...ux.com>
Subject: Re: [PATCH] PCI/sysfs: Fix double free in error path

[+cc Sergey, Alex, Krzysztof since you all posted similar patches in
the past]

On Fri, Oct 07, 2022 at 09:07:35AM +0200, Sascha Hauer wrote:
> On Fri, Oct 07, 2022 at 08:56:18AM +0200, Sascha Hauer wrote:
> > When pci_create_attr() fails then pci_remove_resource_files() is called
> > which will iterate over the res_attr[_wc] arrays and frees every non
> > NULL entry. To avoid a double free here we have to set the failed entry
> > to NULL in pci_create_attr() when freeing it.
> > 
> 
> You might consider applying this alternative version instead which IMO
> looks a bit better.

Thanks, I agree, I like how this one doesn't set res_attr[] until we
know we're going to return success.

Applied to pci/sysfs for v6.2, thanks!

> -------------------------------8<-----------------------------
> 
> From fe8e0e6f914c14395c751b7dc165967b12427995 Mon Sep 17 00:00:00 2001
> From: Sascha Hauer <s.hauer@...gutronix.de>
> Date: Fri, 7 Oct 2022 07:35:35 +0200
> Subject: [PATCH] PCI/sysfs: Fix double free in error path
> 
> When pci_create_attr() fails then pci_remove_resource_files() is called
> which will iterate over the res_attr[_wc] arrays and frees every non
> NULL entry. To avoid a double free here set the array entry only after
> it's clear we successfully initialized it.
> 
> Fixes: b562ec8f74e4 ("PCI: Don't leak memory if sysfs_create_bin_file() fails")
> Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
> Cc: <stable@...r.kernel.org>
> ---
>  drivers/pci/pci-sysfs.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index fc804e08e3cb5..6dd4050c9f2ed 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -1174,11 +1174,9 @@ static int pci_create_attr(struct pci_dev *pdev, int num, int write_combine)
>  
>  	sysfs_bin_attr_init(res_attr);
>  	if (write_combine) {
> -		pdev->res_attr_wc[num] = res_attr;
>  		sprintf(res_attr_name, "resource%d_wc", num);
>  		res_attr->mmap = pci_mmap_resource_wc;
>  	} else {
> -		pdev->res_attr[num] = res_attr;
>  		sprintf(res_attr_name, "resource%d", num);
>  		if (pci_resource_flags(pdev, num) & IORESOURCE_IO) {
>  			res_attr->read = pci_read_resource_io;
> @@ -1196,10 +1194,17 @@ static int pci_create_attr(struct pci_dev *pdev, int num, int write_combine)
>  	res_attr->size = pci_resource_len(pdev, num);
>  	res_attr->private = (void *)(unsigned long)num;
>  	retval = sysfs_create_bin_file(&pdev->dev.kobj, res_attr);
> -	if (retval)
> +	if (retval) {
>  		kfree(res_attr);
> +		return retval;
> +	}
> +
> +	if (write_combine)
> +		pdev->res_attr_wc[num] = res_attr;
> +	else
> +		pdev->res_attr[num] = res_attr;
>  
> -	return retval;
> +	return 0;
>  }
>  
>  /**
> -- 
> 2.30.2
> 
> -- 
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