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Date: Tue, 9 May 2017 23:49:57 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Al Viro <viro@...IV.linux.org.uk>
Cc: Christoph Hellwig <hch@...radead.org>,
	Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...nel.org>,
	Greg KH <greg@...ah.com>, Thomas Garnier <thgarnie@...gle.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Dave Hansen <dave.hansen@...el.com>, Arnd Bergmann <arnd@...db.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Howells <dhowells@...hat.com>,
	René Nyffenegger <mail@...enyffenegger.ch>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Eric W . Biederman" <ebiederm@...ssion.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
	Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>,
	Paolo Bonzini <pbonzini@...hat.com>, Rik van Riel <riel@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Borislav Petkov <bp@...en8.de>, Brian Gerst <brgerst@...il.com>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Russell King <linux@...linux.org.uk>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Mark Rutland <mark.rutland@....com>,
	James Morse <james.morse@....com>,
	linux-s390 <linux-s390@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	Kernel Hardening <kernel-hardening@...ts.openwall.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Re: [PATCH v9 1/4] syscalls: Verify address
 limit before returning to user-mode

On Wed, May 10, 2017 at 03:45:24AM +0100, Al Viro wrote:
> FWIW, some parts of that queue are obviously sane; it's the conversions of
> kernel_write() and friends to ->read_iter/->write_iter() that are non-starters.

And that part is the main point!

> That stuff is used in too many situations; we can't guarantee that all of
> them will be for files that have those.

That's why this series handles ITER_KVEC for this case, which is all
that's really needed for kernel_read/write.  If you insiste the bvec
and pipe cases are handled as well that couod be added fairly easily.

> As for default_file_splice_read(), I seriously suspect that with your change
> we could as well just make it return -EINVAL and be done with that; places
> that have ->read_iter() tend to have explicit ->splice_read() and it looks
> like the ones that do not should simply use generic_file_read_iter().
> I hadn't checked that, but there's not a lot of those:

Making ->splice_read to default to the ->read_iter based implementation
and returning -EINVAL if neither that nor an explicit ->splice_read
is provided is useful, but wasn't the aim of this series.  Similar
on the write side.

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