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Date: Tue, 9 May 2017 23:49:57 -0700
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Subject: Re: [kernel-hardening] Re: [PATCH v9 1/4] syscalls: Verify address
 limit before returning to user-mode
List-Archive: <https://lore.kernel.org/kernel-hardening/>
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To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>, Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>, Greg KH <greg@kroah.com>, Thomas Garnier <thgarnie@google.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, Dave Hansen <dave.hansen@intel.com>, Arnd Bergmann <arnd@arndb.de>, Thomas Gleixner <tglx@linutronix.de>, David Howells <dhowells@redhat.com>, =?iso-8859-1?Q?Ren=E9?= Nyffenegger <mail@renenyffenegger.ch>, Andrew Morton <akpm@linux-foundation.org>, "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>, "Eric W . Biederman" <ebiederm@xmission.com>, Oleg Nesterov <oleg@redhat.com>, Pavel Tikhomirov <ptikhomirov@virtuozzo.com>, Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>, Paolo Bonzini <pbonzini@redhat.com>, Rik van Riel <riel@redhat.com>, Kees Cook <keescook@chromium.org>, Josh Poimboeuf <jpoimboe@redhat.com>, Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Russell King <linux@armlinux.org.uk>, Will Deacon <will.deacon@arm.com>, Catalin Marinas <catalin.marinas@arm.com>, Mark Rutland <mark.rutland@arm.com>, James Morse <james.morse@arm.com>, linux-s390 <linux-s390@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>, Linux API <linux-api@vger.kernel.org>, the arch/x86 maintainers <x86@kernel.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, Kernel Hardening <kernel-hardening@lists.openwall.com>, Linus Torvalds <torvalds@linux-foundation.org>, Peter Zijlstra <a.p.zijlstra@chello.nl>
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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.