From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joonwon Kang Date: Wed, 31 Jul 2019 16:25:37 +0000 Subject: Re: [PATCH] randstruct: fix a bug in is_pure_ops_struct() Message-Id: <20190731162537.GA23152@host> List-Id: References: <20190727155841.GA13586@host> <201907301008.622218EE5@keescook> In-Reply-To: <201907301008.622218EE5@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Kees Cook Cc: re.emese@gmail.com, kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org, jinb.park7@gmail.com 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 > > 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