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Date: Mon, 3 Nov 2025 10:05:31 +0900
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Miaoqian Lin <linmq006@gmail.com>,
	Thomas =?iso-8859-1?Q?Wei=DFschuh?= <linux@weissschuh.net>,
	Wolfram Sang <wsa+renesas@sang-engineering.com>,
	Ruan Jinjie <ruanjinjie@huawei.com>,
	Luca Ceresoli <luca.ceresoli@bootlin.com>,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] misc: eeprom/idt_89hpesx: prevent bad user input in
 idt_dbgfs_csr_write()
Message-ID: <2025110351-mountain-absently-f9f1@gregkh>
References: <20251030052834.97991-1-linmq006@gmail.com>
 <0f712780-8af0-4894-b75c-44fd7390dc3e@app.fastmail.com>
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In-Reply-To: <0f712780-8af0-4894-b75c-44fd7390dc3e@app.fastmail.com>

On Thu, Oct 30, 2025 at 09:47:22AM +0100, Arnd Bergmann wrote:
> On Thu, Oct 30, 2025, at 06:28, Miaoqian Lin wrote:
> > A malicious user could pass an arbitrarily bad value
> > to memdup_user_nul(), potentially causing kernel crash.
> 
> I think you should be more specific than 'kernel crash' here.
> As far as I can tell, the worst case would be temporarily
> consuming a MAX_ORDER_NR_PAGES allocation, leading to out-of-memory.

I think we already limit the size of writes so this shouldn't happen,
but a real trace would be good to see.

> > Fixes: 183238ffb886 ("misc: eeprom/idt_89hpesx: Switch to 
> > memdup_user_nul() helper")
> 
> I don't think that patch changed anything, the same thing
> would have happened with kmalloc()+copy_from_user().
> Am I missing something?
> 
> > +	if (count == 0 || count > PAGE_SIZE)
> > +		return -EINVAL;
> > +
> 
> How did you pick PAGE_SIZE as the maximum here?

I agree, that seems very very small.

thanks,

greg k-h