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Date: Thu, 1 Aug 2019 01:25:37 +0900
From: Joonwon Kang <kjw1627@...il.com>
To: Kees Cook <keescook@...omium.org>
Cc: re.emese@...il.com, kernel-hardening@...ts.openwall.com,
linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
jinb.park7@...il.com
Subject: Re: [PATCH] randstruct: fix a bug in is_pure_ops_struct()
On Tue, Jul 30, 2019 at 10:11:19AM -0700, Kees Cook wrote:
> On Sun, Jul 28, 2019 at 12:58:41AM +0900, Joonwon Kang wrote:
> > Before this, there were false negatives in the case where a struct
> > contains other structs which contain only function pointers because
> > of unreachable code in is_pure_ops_struct().
>
> Ah, very true. Something like:
>
> struct internal {
> void (*callback)(void);
> };
>
> struct wrapper {
> struct internal foo;
> void (*other_callback)(void);
> };
>
> would have not been detected as is_pure_ops_struct()?
>
> How did you notice this? (Are there cases of this in the kernel?)
When I compiled kernel with allyesconfig, there seemed to be no such cases,
but I found the bug just by code review and test.
However, I would like to slightly modify this patch and add one more patch.
I will send the patch set soon.
>
> > Signed-off-by: Joonwon Kang <kjw1627@...il.com>
>
> Applied; thanks!
>
> -Kees
>
> > ---
> > scripts/gcc-plugins/randomize_layout_plugin.c | 11 +++++------
> > 1 file changed, 5 insertions(+), 6 deletions(-)
> >
> > diff --git a/scripts/gcc-plugins/randomize_layout_plugin.c b/scripts/gcc-plugins/randomize_layout_plugin.c
> > index 6d5bbd31db7f..a123282a4fcd 100644
> > --- a/scripts/gcc-plugins/randomize_layout_plugin.c
> > +++ b/scripts/gcc-plugins/randomize_layout_plugin.c
> > @@ -443,13 +443,12 @@ static int is_pure_ops_struct(const_tree node)
> > if (node == fieldtype)
> > continue;
> >
> > - if (!is_fptr(fieldtype))
> > - return 0;
> > -
> > - if (code != RECORD_TYPE && code != UNION_TYPE)
> > - continue;
> > + if (code == RECORD_TYPE || code == UNION_TYPE) {
> > + if (!is_pure_ops_struct(fieldtype))
> > + return 0;
> > + }
> >
> > - if (!is_pure_ops_struct(fieldtype))
> > + if (!is_fptr(fieldtype))
> > return 0;
> > }
> >
> > --
> > 2.17.1
> >
>
> --
> Kees Cook
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