Re: [ovs-dev] [PATCH net] net: openvswitch: fix overwriting ct original tuple for ICMPv6

[Eelco Chaudron <echaudro@redhat.com>]

On 9 May 2024, at 11:38, Ilya Maximets wrote:

> OVS_PACKET_CMD_EXECUTE has 3 main attributes:
>  - OVS_PACKET_ATTR_KEY - Packet metadata in a netlink format.
>  - OVS_PACKET_ATTR_PACKET - Binary packet content.
>  - OVS_PACKET_ATTR_ACTIONS - Actions to execute on the packet.
>
> OVS_PACKET_ATTR_KEY is parsed first to populate sw_flow_key structure
> with the metadata like conntrack state, input port, recirculation id,
> etc.  Then the packet itself gets parsed to populate the rest of the
> keys from the packet headers.
>
> Whenever the packet parsing code starts parsing the ICMPv6 header, it
> first zeroes out fields in the key corresponding to Neighbor Discovery
> information even if it is not an ND packet.
>
> It is an 'ipv6.nd' field.  However, the 'ipv6' is a union that shares
> the space between 'nd' and 'ct_orig' that holds the original tuple
> conntrack metadata parsed from the OVS_PACKET_ATTR_KEY.
>
> ND packets should not normally have conntrack state, so it's fine to
> share the space, but normal ICMPv6 Echo packets or maybe other types of
> ICMPv6 can have the state attached and it should not be overwritten.
>
> The issue results in all but the last 4 bytes of the destination
> address being wiped from the original conntrack tuple leading to
> incorrect packet matching and potentially executing wrong actions
> in case this packet recirculates within the datapath or goes back
> to userspace.
>
> ND fields should not be accessed in non-ND packets, so not clearing
> them should be fine.  Executing memset() only for actual ND packets to
> avoid the issue.
>
> Initializing the whole thing before parsing is needed because ND packet
> may not contain all the options.
>
> The issue only affects the OVS_PACKET_CMD_EXECUTE path and doesn't
> affect packets entering OVS datapath from network interfaces, because
> in this case CT metadata is populated from skb after the packet is
> already parsed.
>
> Fixes: 9dd7f8907c37 ("openvswitch: Add original direction conntrack tuple to sw_flow_key.")
> Reported-by: Antonin Bas <antonin.bas@broadcom.com>
> Closes: https://github.com/openvswitch/ovs-issues/issues/327
> Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

This patch looks good to me.

Acked-by: Eelco Chaudron <echaudro@redhat.com>

> ---
>
> Note: I'm working on a selftest for this issue, but it requires some
> ground work first to add support for OVS_PACKET_CMD_EXECUTE into
> opnevswitch selftests as well as parsing of ct tuples.  So it is going
> to be a separate patch set.
>
>  net/openvswitch/flow.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
> index 33b21a0c0548..8a848ce72e29 100644
> --- a/net/openvswitch/flow.c
> +++ b/net/openvswitch/flow.c
> @@ -561,7 +561,6 @@ static int parse_icmpv6(struct sk_buff *skb, struct sw_flow_key *key,
>  	 */
>  	key->tp.src = htons(icmp->icmp6_type);
>  	key->tp.dst = htons(icmp->icmp6_code);
> -	memset(&key->ipv6.nd, 0, sizeof(key->ipv6.nd));
>
>  	if (icmp->icmp6_code == 0 &&
>  	    (icmp->icmp6_type == NDISC_NEIGHBOUR_SOLICITATION ||
> @@ -570,6 +569,8 @@ static int parse_icmpv6(struct sk_buff *skb, struct sw_flow_key *key,
>  		struct nd_msg *nd;
>  		int offset;
>
> +		memset(&key->ipv6.nd, 0, sizeof(key->ipv6.nd));
> +
>  		/* In order to process neighbor discovery options, we need the
>  		 * entire packet.
>  		 */
> -- 
> 2.44.0
>
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