netdev - Re: v4.14-rc2/arm64 kernel BUG at net/core/skbuff.c:2626

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Date:   Mon, 2 Oct 2017 18:21:32 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        syzkaller <syzkaller@...glegroups.com>,
        "David S. Miller" <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: v4.14-rc2/arm64 kernel BUG at net/core/skbuff.c:2626

On Mon, Oct 02, 2017 at 07:48:28AM -0700, Eric Dumazet wrote:
> Please try the following fool proof patch.
>
> This is what I had in my local tree back in August but could not
> conclude on the syzkaller bug I was working on.
> 
> diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
> index 681e33998e03b609fdca83a83e0fc62a3fee8c39..e51d777797a927058760a1ab7af00579f7488cb5 100644
> --- a/net/ipv4/icmp.c
> +++ b/net/ipv4/icmp.c
> @@ -732,7 +732,8 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
>  		room = 576;
>  	room -= sizeof(struct iphdr) + icmp_param.replyopts.opt.opt.optlen;
>  	room -= sizeof(struct icmphdr);
> -
> +	if (room < 0)
> +		goto ende;
>  	icmp_param.data_len = skb_in->len - icmp_param.offset;
>  	if (icmp_param.data_len > room)
>  		icmp_param.data_len = room;
> 

Unfortuantely, with this applied I still see the issue.

Syzkaller came up with a minimized reproducer [1], which can trigger the
issue near instantly under syz-execprog. If there's anything that would
help to narrow this down, I'm more than happy to give it a go.

Thanks,
Mark.

[1] https://www.kernel.org/pub/linux/kernel/people/mark/bugs/20171002-skb_clone-misaligned-atomic/syzkaller.repro