netdev - Re: [PATCH] seg6: Fix slab-out-of-bounds in fl6_update

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Date:   Tue, 2 Jun 2020 06:20:53 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     YueHaibing <yuehaibing@...wei.com>, davem@...emloft.net,
        kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org, kuba@...nel.org,
        alex.aring@...il.com, ahabdels@...il.com
Cc:     netdev@...r.kernel.org, Ahmed Abdelsalam <ahabdels@...il.com>,
        David Lebrun <david.lebrun@...ouvain.be>
Subject: Re: [PATCH] seg6: Fix slab-out-of-bounds in fl6_update_dst()



On 6/1/20 11:51 PM, YueHaibing wrote:
> When update flowi6 daddr in fl6_update_dst() for srcrt, the used index
> of segments should be segments_left minus one per RFC8754
> (section 4.3.1.1) S15 S16. Otherwise it may results in an out-of-bounds
> read.
> 
> Reported-by: syzbot+e8c028b62439eac42073@...kaller.appspotmail.com
> Fixes: 0cb7498f234e ("seg6: fix SRH processing to comply with RFC8754")
> Signed-off-by: YueHaibing <yuehaibing@...wei.com>
> ---
>  net/ipv6/exthdrs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
> index 5a8bbcdcaf2b..f5304bf33ab1 100644
> --- a/net/ipv6/exthdrs.c
> +++ b/net/ipv6/exthdrs.c
> @@ -1353,7 +1353,7 @@ struct in6_addr *fl6_update_dst(struct flowi6 *fl6,
>  	{
>  		struct ipv6_sr_hdr *srh = (struct ipv6_sr_hdr *)opt->srcrt;
>  
> -		fl6->daddr = srh->segments[srh->segments_left];
> +		fl6->daddr = srh->segments[srh->segments_left - 1];
>  		break;
>  	}
>  	default:
> 

1) Any reason you do not cc the author of the buggy patch ?
   I also cced David Lebrun <david.lebrun@...ouvain.be> to get more eyes.

2) What happens if segments_left == 0 ?