netdev - Re: [PATCH iproute2] iptunnel: detect protocol mismatch on tunnel change

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Date:   Tue, 11 Apr 2023 09:55:25 -0600
From:   David Ahern <dsahern@...nel.org>
To:     Stephen Hemminger <stephen@...workplumber.org>,
        netdev@...r.kernel.org
Cc:     bluca@...ian.org, Robin <imer@...r.cc>
Subject: Re: [PATCH iproute2] iptunnel: detect protocol mismatch on tunnel
 change

On 4/10/23 5:35 PM, Stephen Hemminger wrote:
> diff --git a/ip/iptunnel.c b/ip/iptunnel.c
> index 02c3670b469d..b6da145913d6 100644
> --- a/ip/iptunnel.c
> +++ b/ip/iptunnel.c
> @@ -17,6 +17,7 @@
>  #include <net/if_arp.h>
>  #include <linux/ip.h>
>  #include <linux/if_tunnel.h>
> +#include <linux/ip6_tunnel.h>
>  
>  #include "rt_names.h"
>  #include "utils.h"
> @@ -172,11 +173,20 @@ static int parse_args(int argc, char **argv, int cmd, struct ip_tunnel_parm *p)
>  			if (get_ifname(p->name, *argv))
>  				invarg("\"name\" not a valid ifname", *argv);
>  			if (cmd == SIOCCHGTUNNEL && count == 0) {
> -				struct ip_tunnel_parm old_p = {};
> +				union {
> +					struct ip_tunnel_parm ip_tnl;
> +					struct ip6_tnl_parm2 ip6_tnl;
> +				} old_p = {};'

That addresses the stack smashing, but ....

>  
>  				if (tnl_get_ioctl(*argv, &old_p))
>  					return -1;
> -				*p = old_p;
> +
> +				if (old_p.ip_tnl.iph.version != 4 ||
> +				    old_p.ip_tnl.iph.ihl != 5)

this field overlays laddr in ip6_tnl_parm2 which means there is a
collision in valid addresses.


> +					invarg("\"name\" is not an ip tunnel",
> +					       *argv);
> +
> +				*p = old_p.ip_tnl;
>  			}
>  		}
>  		count++;