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Date: Fri, 12 May 2017 01:07:41 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Al Viro <viro@...IV.linux.org.uk>
Cc: Ingo Molnar <mingo@...nel.org>, Andy Lutomirski <luto@...nel.org>,
	Christoph Hellwig <hch@...radead.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>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Palash Bandyopadhyay <palash.bandyopadhyay@...exant.com>,
	Eric Van Hensbergen <ericvh@...il.com>,
	Richard Weinberger <richard@....at>
Subject: Re: Re: [PATCH v9 1/4] syscalls: Verify address
 limit before returning to user-mode

On Fri, May 12, 2017 at 12:35:21AM -0700, Christoph Hellwig wrote:
> On Fri, May 12, 2017 at 08:15:49AM +0100, Al Viro wrote:
> > And converting everything to ->read_iter()/->write_iter() means an insane
> > amount of code churn, not to mention coping with random bogosities in
> > semantics.  ->read() and ->write() are going to stay around, pretty
> > much indefinitely.
> 
> But I don't think kernel users of them have to.  I've been digging
> through the calllers and will send an analysis to the list in a bit.

Ok, here is the cleaned up list.  The targets for in-kernel I/O
are basically regular files on normal fs, block devices, pipes
and sockets, with a few narrow exceptions and a few unclear cases.

I've added a few maintainers to Cc to clarify, and the list is below:

When looking at kernel_read/kernel_readv/kernel_write/__kernel_write
instances, or vfs_read/vfs_readv/vfs_write/vfs_writev inststances with
set_fs tricks most of them simply require a regular file on a "real"
fs or a block device, pipe, socket:

 - various binary loaders: need to be regular files (+ on a "real" fs)
 - nandsim: expect a regular file or maybe a block device
 - code: expects a regular file
 - ecryptfs: expects a regular file
 - splice: can be a regular file or device file
 - security/keys: regular file
 - cachefiles: needs to be a regular file
 - coredump: usually a regular file, but possibly a pipe
 - acct: regular file
 - target: regular file
 - nfsd: regular file
 - lustre: regular file
 - f_mass_storage: regular file, or maybe block device
 - autofs: pipe
 - btrfs: regular file / pipe / socket
 - ima: regular file on specific file systems

Then there are a few interesting ones with specific targets:

 - sysctl: regular file on procfs
 - mconsole: procfs as far as I can tell.  Might be able to further
   narrow it down?
 - ashmem: regular file on shmem

The nommu mmap code needs to read everything that wants to support
a MAP_PRIVATE mmap, but as far as a I can tell: do a) address limits
not matter for nommu, and b) I have no f***cking idea why it doesn't
use readpage(s) to start with like the MMU code.

And a few that I can't figure:

 - cx25821: no idea what this opens, need to confirm with the maintainers
   (on Cc)
 - 9p: not clear.  looks like it might be sockets/pipes
 
 Last but not least we have a driver that's a complete mess:

 - series2002: /dev/tty* (drivers is in staging and needs to be rewritten
   using the proper in-kernel APIs anyway)
 

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