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Message-ID: <201907301008.622218EE5@keescook>
Date: Tue, 30 Jul 2019 10:11:19 -0700
From: Kees Cook <keescook@...omium.org>
To: Joonwon Kang <kjw1627@...il.com>
Cc: re.emese@...il.com, kernel-hardening@...ts.openwall.com,
linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] randstruct: fix a bug in is_pure_ops_struct()
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?)
> 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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