linux-kernel - Re: [kernel-hardening] [PATCH 17/23] dcache: define usercopy region in dentry

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Date:   Wed, 28 Jun 2017 09:55:20 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        David Windsor <dave@...lcore.net>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [kernel-hardening] [PATCH 17/23] dcache: define usercopy region
 in dentry_cache slab cache

On Wed, Jun 28, 2017 at 09:44:13AM -0700, Kees Cook wrote:
> On Mon, Jun 19, 2017 at 9:08 PM, Eric Biggers <ebiggers3@...il.com> wrote:
> > On Mon, Jun 19, 2017 at 04:36:31PM -0700, Kees Cook wrote:
> >> From: David Windsor <dave@...lcore.net>
> >>
> >> When a dentry name is short enough, it can be stored directly in
> >> the dentry itself.  These dentry short names, stored in struct
> >> dentry.d_iname and therefore contained in the dentry_cache slab cache,
> >> need to be coped to/from userspace.
> >>
> >> In support of usercopy hardening, this patch defines a region in
> >> the dentry_cache slab cache in which userspace copy operations
> >> are allowed.
> >>
> >> This region is known as the slab cache's usercopy region.  Slab
> >> caches can now check that each copy operation involving cache-managed
> >> memory falls entirely within the slab's usercopy region.
> >>
> >> This patch is modified from Brad Spengler/PaX Team's PAX_USERCOPY
> >> whitelisting code in the last public patch of grsecurity/PaX based on my
> >> understanding of the code. Changes or omissions from the original code are
> >> mine and don't reflect the original grsecurity/PaX code.
> >>
> >
> > For all these patches please mention *where* the data is being copied to/from
> > userspace.
> 
> Can you explain what you mean here? The field being copied is already
> mentioned in the commit log; do you mean where in the kernel source
> does the copy happen?
> 

Yes, for the ones where it isn't obvious, mentioning a syscall or ioctl might be
sufficient.  Others may need more explanation.

Eric