Subject: Re: [PATCH 13/18] ipv6: prevent bounds-check bypass via speculative execution

From: Stephen Hemminger <[email-masked]>
Date: Sat, 6 Jan 2018 06:48:52 -0800

On Fri, 05 Jan 2018 17:11:04 -0800
Dan Williams <[email-masked]> wrote:

> Static analysis reports that 'offset' may be a user controlled value
> that is used as a data dependency reading from a raw6_frag_vec buffer.
> In order to avoid potential leaks of kernel memory values, block
> speculative execution of the instruction stream that could issue further
> reads based on an invalid '*(rfv->c + offset)' value.
> 
> Based on an original patch by Elena Reshetova.
> 
> Cc: "David S. Miller" <[email-masked]>
> Cc: Alexey Kuznetsov <[email-masked]>
> Cc: Hideaki YOSHIFUJI <[email-masked]>
> Cc: [email-masked]
> Signed-off-by: Elena Reshetova <[email-masked]>
> Signed-off-by: Dan Williams <[email-masked]>
> ---
>  net/ipv6/raw.c |    9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
> index 761a473a07c5..384e3d59d148 100644
> --- a/net/ipv6/raw.c
> +++ b/net/ipv6/raw.c
> @@ -33,6 +33,7 @@
>  #include <linux/skbuff.h>
>  #include <linux/compat.h>
>  #include <linux/uaccess.h>
> +#include <linux/compiler.h>
>  #include <asm/ioctls.h>
>  
>  #include <net/net_namespace.h>
> @@ -725,17 +726,17 @@ static int raw6_getfrag(void *from, char *to, int offset, int len, int odd,
>  		       struct sk_buff *skb)
>  {
>  	struct raw6_frag_vec *rfv = from;
> +	char *rfv_buf;
>  
> -	if (offset < rfv->hlen) {
> +	if ((rfv_buf = nospec_array_ptr(rfv->c, offset, rfv->hlen))) {
>  		int copy = min(rfv->hlen - offset, len);

Minor nit.

Please don't do assignment in condition test here.
Instead.
	rfv_buf = nospec_array_ptr(rfv->c, offset, rfv->hlen);
	if (rfv_buf) {