netdev - RE: [PATCH RFC] Introduce uniptr_t as a generic "universal" pointer

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Date: Mon, 14 Aug 2023 16:06:27 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Linus Torvalds' <torvalds@...ux-foundation.org>, Takashi Iwai
	<tiwai@...e.de>
CC: Christoph Hellwig <hch@....de>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Andy Shevchenko
	<andriy.shevchenko@...ux.intel.com>, Mark Brown <broonie@...nel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH RFC] Introduce uniptr_t as a generic "universal" pointer

From: Linus Torvalds 
> Sent: 09 August 2023 16:59
> 
> On Wed, 9 Aug 2023 at 07:44, Takashi Iwai <tiwai@...e.de> wrote:
> >
> > The remaining question is whether the use of sockptr_t for other
> > subsystems as a generic pointer is a recommended / acceptable move...
> 
> Very much not recommended. sockptr_t is horrible too, but it was (part
> of) what made it possible to fix an even worse horrible historical
> mistake (ie getting rid of set_fs()).
> 
> So I detest sockptr_t. It's garbage. At the very minimum it should
> have had the length associated with it, not passed separately.

FWIW I've thought you'd want something like:
struct ptr_arg {
	void          *kernel;
	void __user   *user;
	unsigned int  kernel_len;
	unsigned int  user_len;
};

Then [gs]etsockopt() could copy short user buffers into
kernel space (eg on stack) while allowing code that needs
very large buffers (eg some sctp options) to directly
access a userspace buffer.

There certainly used to be sockopt calls where the user
didn't pass the correct/any length.
They might all have been in decnet.

	David

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