linux-kernel - Re: [PATCH v4] usb: core: Add "quirks" parameter for usbcore

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Message-ID: <20180228144729.GE20414@bombadil.infradead.org>
Date:   Wed, 28 Feb 2018 06:47:29 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     gregkh@...uxfoundation.org, oneukum@...e.com, corbet@....net,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH v4] usb: core: Add "quirks" parameter for usbcore

On Mon, Feb 26, 2018 at 11:04:57PM +0800, Kai-Heng Feng wrote:
> +static char quirks_param[128];
> +module_param_string(quirks, quirks_param, sizeof(quirks_param), 0644);
> +MODULE_PARM_DESC(quirks, "Add/modify USB quirks by specifying quirks=vendorID:productID:quirks");
> +
> +static char quirks_param_orig[128];

> +static u32 usb_detect_dynamic_quirks(struct usb_device *udev)
> +{
> +	u16 vid = le16_to_cpu(udev->descriptor.idVendor);
> +	u16 pid = le16_to_cpu(udev->descriptor.idProduct);
> +	struct quirk_entry *quirk;
> +
> +	mutex_lock(&quirk_mutex);
> +	if (strcmp(quirks_param, quirks_param_orig) != 0) {
> +		strcpy(quirks_param_orig, quirks_param);

What happens if the user is writing to quirks_param at the same time
that you memcpy it?

I think you're going about this wrong by trying to use the
module_param_string machinery.  You should be using module_param_cb()
to build the quirks list when the user writes it (and then translate
back into a string when the user wants to read from it.
Also, you won't need to use a linked list for this; you can just allocate
an array of quirks.