Subject: Re: BUG: KASAN: stack-out-of-bounds in __ip_options_echo

From: Florian Westphal <[email-masked]>
Date: Fri, 5 May 2023 07:58:22 +0200

Fengtao (fengtao, Euler) <[email-masked]> wrote:
> Hi
> 
> I have tested the patch, the panic not happend.
> And I search the similar issue in kernel, and found commit:
> [1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ed0de45a1008
> [2]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3da1ed7ac398
> 
> So I tested another patch like this:
> ------------[ cut here ]------------
> --- .//net/ipv4/netfilter/nf_reject_ipv4.c      2023-05-02 13:03:35.427896081 +0000
> +++ .//net/ipv4/netfilter/nf_reject_ipv4.c.new  2023-05-02 13:03:00.433897970 +0000
> @@ -187,6 +187,7 @@ > 
>  void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
>  {
> +       struct ip_options opt;
>         struct iphdr *iph = ip_hdr(skb_in);
>         u8 proto = iph->protocol;
> 
> @@ -196,13 +197,18 @@
>         if (hook == NF_INET_PRE_ROUTING && nf_reject_fill_skb_dst(skb_in))
>                 return;
> 
> +       memset(&opt, 0, sizeof(opt));
> +       opt.optlen = iph->ihl*4 - sizeof(struct iphdr);
> +       if (__ip_options_compile(dev_net(skb_in->dev), &opt, skb_in, NULL))
> +               return;
> +
>         if (skb_csum_unnecessary(skb_in) || !nf_reject_verify_csum(proto)) {
> -               icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
> +               __icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0, &opt);
>                 return;
>         }
> 
>         if (nf_ip_checksum(skb_in, hook, ip_hdrlen(skb_in), proto) == 0)
> -               icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
> +               __icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0, &opt);
>  }
>  EXPORT_SYMBOL_GPL(nf_send_unreach);
> ------------[ cut here ]------------
> 
> This can also fix the issue :)

No, it papers over the problem, by only fixing this specific instance
(icmpv4).  What about ipv6?  What about all other IPCB accesses?

> BTW, I think the problem is more then ipvlan? Maybe some other scenarios that can trigger such issue.

Such as?

I don't see how this is fixable, just have have a look at "git grep
IPCB", how do you envision stack to know how such access is valid or
not?