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Date: Thu, 21 May 2026 08:19:16 +0200
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: David Laight <david.laight.linux@gmail.com>
Cc: driver-core@lists.linux.dev, linux-kernel@vger.kernel.org,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Danilo Krummrich <dakr@kernel.org>, NeilBrown <neil@brown.name>,
	Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH] sysfs: clamp show() return value in sysfs_kf_read()
Message-ID: <2026052148-glamorous-hassle-2cc8@gregkh>
References: <2026052000-drove-unicycle-d61b@gregkh>
 <20260520231158.407ebf0b@pumpkin>
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In-Reply-To: <20260520231158.407ebf0b@pumpkin>

On Wed, May 20, 2026 at 11:11:58PM +0100, David Laight wrote:
> On Wed, 20 May 2026 15:07:01 +0200
> Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> 
> > sysfs_kf_seq_show() defends against buggy show() callbacks that return
> > larger than PAGE_SIZE by clamping the value and printing a warning.
> > sysfs_kf_read(), the prealloc variant, has no such defense.
> > 
> > The only current in-tree user of __ATTR_PREALLOC is drivers/md/md.c,
> > whose show() callbacks are well-behaved, so this is hardening against
> > future drivers doing foolish things and out-of-tree code doing even more
> > foolish things.
> 
> What is the rational for it using PREALLOC?

No idea, you might want to dig to find the commit that did this.

thanks,

greg k-h