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

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Date:   Sat, 6 Jan 2018 13:04:05 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Dan Williams <dan.j.williams@...el.com>,
        linux-kernel@...r.kernel.org
Cc:     linux-arch@...r.kernel.org,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        netdev@...r.kernel.org, peterz@...radead.org,
        gregkh@...uxfoundation.org,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>, tglx@...utronix.de,
        torvalds@...ux-foundation.org,
        "David S. Miller" <davem@...emloft.net>,
        Elena Reshetova <elena.reshetova@...el.com>,
        alan@...ux.intel.com
Subject: Re: [PATCH 13/18] ipv6: prevent bounds-check bypass via speculative
 execution

On 1/6/2018 4:11 AM, Dan Williams 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" <davem@...emloft.net>
> Cc: Alexey Kuznetsov <kuznet@....inr.ac.ru>
> Cc: Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
> Cc: netdev@...r.kernel.org
> Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
>   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
[...]
> @@ -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))) {

    And here...

>   		int copy = min(rfv->hlen - offset, len);
>   
>   		if (skb->ip_summed == CHECKSUM_PARTIAL)
> -			memcpy(to, rfv->c + offset, copy);
> +			memcpy(to, rfv_buf, copy);
>   		else
>   			skb->csum = csum_block_add(
>   				skb->csum,
> -				csum_partial_copy_nocheck(rfv->c + offset,
> -							  to, copy, 0),
> +				csum_partial_copy_nocheck(rfv_buf, to, copy, 0),
>   				odd);
>   
>   		odd = 0;

MBR, Sergei