netdev - Re: [PATCH net 1/2] bridge: Avoid infinite loop when suppressing NS messages with invalid options

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Message-ID: <7e2ffbf7-b756-04ee-1210-a11fd26d1237@cumulusnetworks.com>
Date:   Mon, 1 Jun 2020 16:02:16 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Ido Schimmel <idosch@...sch.org>, netdev@...r.kernel.org,
        bridge@...ts.linux-foundation.org
Cc:     davem@...emloft.net, kuba@...nel.org, roopa@...ulusnetworks.com,
        dlstevens@...ibm.com, allas@...lanox.com, mlxsw@...lanox.com,
        Ido Schimmel <idosch@...lanox.com>
Subject: Re: [PATCH net 1/2] bridge: Avoid infinite loop when suppressing NS
 messages with invalid options

On 01/06/2020 15:58, Ido Schimmel wrote:
> From: Ido Schimmel <idosch@...lanox.com>
> 
> When neighbor suppression is enabled the bridge device might reply to
> Neighbor Solicitation (NS) messages on behalf of remote hosts.
> 
> In case the NS message includes the "Source link-layer address" option
> [1], the bridge device will use the specified address as the link-layer
> destination address in its reply.
> 
> To avoid an infinite loop, break out of the options parsing loop when
> encountering an option with length zero and disregard the NS message.
> 
> This is consistent with the IPv6 ndisc code and RFC 4886 which states
> that "Nodes MUST silently discard an ND packet that contains an option
> with length zero" [2].
> 
> [1] https://tools.ietf.org/html/rfc4861#section-4.3
> [2] https://tools.ietf.org/html/rfc4861#section-4.6
> 
> Fixes: ed842faeb2bd ("bridge: suppress nd pkts on BR_NEIGH_SUPPRESS ports")
> Signed-off-by: Ido Schimmel <idosch@...lanox.com>
> Reported-by: Alla Segal <allas@...lanox.com>
> Tested-by: Alla Segal <allas@...lanox.com>
> ---
>  net/bridge/br_arp_nd_proxy.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/bridge/br_arp_nd_proxy.c b/net/bridge/br_arp_nd_proxy.c
> index 37908561a64b..b18cdf03edb3 100644
> --- a/net/bridge/br_arp_nd_proxy.c
> +++ b/net/bridge/br_arp_nd_proxy.c
> @@ -276,6 +276,10 @@ static void br_nd_send(struct net_bridge *br, struct net_bridge_port *p,
>  	ns_olen = request->len - (skb_network_offset(request) +
>  				  sizeof(struct ipv6hdr)) - sizeof(*ns);
>  	for (i = 0; i < ns_olen - 1; i += (ns->opt[i + 1] << 3)) {
> +		if (!ns->opt[i + 1]) {
> +			kfree_skb(reply);
> +			return;
> +		}
>  		if (ns->opt[i] == ND_OPT_SOURCE_LL_ADDR) {
>  			daddr = ns->opt + i + sizeof(struct nd_opt_hdr);
>  			break;
> 

Good catch!
Acked-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>