linux-kernel - Re: [PATCH net v2] net: mdio-ipq4019: fix possible invalid pointer dereference

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Message-ID: <3cb5a576-8eb7-54fc-4f4b-9db360b6713d@huawei.com>
Date:   Sat, 19 Nov 2022 13:41:05 +0800
From:   Hui Tang <tanghui20@...wei.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <mw@...ihalf.com>, <linux@...linux.org.uk>, <pabeni@...hat.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <yusongping@...wei.com>
Subject: Re: [PATCH net v2] net: mdio-ipq4019: fix possible invalid pointer
 dereference



On 2022/11/18 21:44, Andrew Lunn wrote:
>> So, the code should be as follows, is that right?
>>
>> +	void __iomem *devm_ioremap_resource_optional(struct device *dev,
>> +                                    	     const struct resource *res)
>> +	{
>> +		void __iomem *base;
>> +
>> +		base = __devm_ioremap_resource(dev, res, DEVM_IOREMAP);
>> +		if (IS_ERR(base) && PTR_ERR(base) == -ENOMEM)
>> +			return NULL;
>> +
>> +		return base;
>> +	}
>>
>>
>> [...]
>> 	res = platform_get_resource(pdev, IORESOURCE_MEM, 1);
>> -	if (res)
>> +	if (res) {
>> +		priv->eth_ldo_rdy = devm_ioremap_resource_optional(&pdev->dev, res)
>> +		if (IS_ERR(priv->eth_ldo_rdy))
>> +			return PTR_ERR(priv->eth_ldo_rdy);
>> +	}
>> [...]
>
> Yes, that is the basic concept.
>
> The only thing i might change is the double meaning of -ENOMEM.
> __devm_ioremap_resource() allocates memory, and if that memory
> allocation fails, it returns -ENOMEM. If the resource does not exist,
> it also returns -ENOMEM. So you cannot tell these two error conditions
> apart. Most of the other get_foo() calls return -ENODEV if the
> gpio/regulator/clock does not exist, so you can tell if you are out of
> memory. But ioremap is specifically about memory so -ENOMEM actually
> makes sense.
>
> If you are out of memory, it seems likely the problem is not going to
> go away quickly, so the next allocation will also fail, and hopefully
> the error handling will then work. So i don't think it is major
> issue. So yes, go with the code above.
>

Hi, Andrew

My new patchset is ready, but I just found out that another patch has been
applied to netdev/net.git. Can I solve the problem in present way? And I
will add devm_ioremap_resource_optional() helper later to optimize related
drivers. How about this?

Thanks.