randstruct: fix a bug in is_pure_ops_struct()
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Message ID 20190727155841.GA13586@host
State New
Headers show
Series
  • randstruct: fix a bug in is_pure_ops_struct()
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Commit Message

Joonwon Kang July 27, 2019, 3:58 p.m. UTC
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().

Signed-off-by: Joonwon Kang <kjw1627@gmail.com>
---
 scripts/gcc-plugins/randomize_layout_plugin.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

Comments

Kees Cook July 30, 2019, 5:11 p.m. UTC | #1
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@gmail.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
>
Joonwon Kang July 31, 2019, 4:25 p.m. UTC | #2
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@gmail.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

Patch
diff mbox series

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;
 	}