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Date: Thu, 24 Jun 2021 18:01:27 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Andreas Roeseler <andreas.a.roeseler@...il.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net,
yoshfuji@...ux-ipv6.org, dsahern@...nel.org, kuba@...nel.org,
willemdebruijn.kernel@...il.com
Subject: Re: [PATCH net-next V2 1/1] ipv6: ICMPV6: add response to ICMPV6 RFC
8335 PROBE messages
On Thu, Jun 24, 2021 at 3:04 PM Andreas Roeseler
<andreas.a.roeseler@...il.com> wrote:
>
> This patch builds off of commit 2b246b2569cd2ac6ff700d0dce56b8bae29b1842
> and adds functionality to respond to ICMPV6 PROBE requests.
No need to structure as a series (1/1) if a single patch, btw.
> Add icmp_build_probe function to construct PROBE requests for both
> ICMPV4 and ICMPV6.
>
> Modify icmpv6_rcv to detect ICMPV6 PROBE messages and call the
> icmpv6_echo_reply handler.
>
> Modify icmpv6_echo_reply to build a PROBE response message based on the
> queried interface.
>
> This patch has been tested using a branch of the iputils git repo which can
> be found here: https://github.com/Juniper-Clinic-2020/iputils/tree/probe-request
>
> Signed-off-by: Andreas Roeseler <andreas.a.roeseler@...il.com>
> ---
> Changes:
> v1 -> v2:
> Suggested by: Willem de Bruijn <willemdebruijn.kernel@...il.com>
> - Do not add sysctl for ICMPV6 PROBE control and instead use existing
> ICMPV4 sysctl.
> - Add icmp_build_probe function to construct PROBE responses for both
> ICMPV4 and ICMPV6.
> ---
> include/net/icmp.h | 1 +
> net/ipv4/icmp.c | 101 +++++++++++++++++++++++++++------------------
> net/ipv6/icmp.c | 24 +++++++++--
> 3 files changed, 83 insertions(+), 43 deletions(-)
>
> diff --git a/include/net/icmp.h b/include/net/icmp.h
> index fd84adc47963..caddf4a59ad1 100644
> --- a/include/net/icmp.h
> +++ b/include/net/icmp.h
> @@ -57,5 +57,6 @@ int icmp_rcv(struct sk_buff *skb);
> int icmp_err(struct sk_buff *skb, u32 info);
> int icmp_init(void);
> void icmp_out_count(struct net *net, unsigned char type);
> +bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr);
>
> #endif /* _ICMP_H */
> diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
> index 0a57f1892e7e..27a6fa29e2d3 100644
> --- a/net/ipv4/icmp.c
> +++ b/net/ipv4/icmp.c
> @@ -977,56 +977,37 @@ static bool icmp_redirect(struct sk_buff *skb)
> return true;
> }
>
> -/*
> - * Handle ICMP_ECHO ("ping") and ICMP_EXT_ECHO ("PROBE") requests.
> +/* Helper for icmp_echo and icmpv6_echo_reply.
> + * Searches for net_device that matches PROBE interface identifier
> + * and builds PROBE reply message in icmphdr.
> *
> - * RFC 1122: 3.2.2.6 MUST have an echo server that answers ICMP echo
> - * requests.
> - * RFC 1122: 3.2.2.6 Data received in the ICMP_ECHO request MUST be
> - * included in the reply.
> - * RFC 1812: 4.3.3.6 SHOULD have a config option for silently ignoring
> - * echo requests, MUST have default=NOT.
> - * RFC 8335: 8 MUST have a config option to enable/disable ICMP
> - * Extended Echo Functionality, MUST be disabled by default
> - * See also WRT handling of options once they are done and working.
> + * Returns false if PROBE responses are disabled via sysctl
> */
>
> -static bool icmp_echo(struct sk_buff *skb)
> +bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr)
It's a bit unusual, but I suggest moving this helper below icmp_echo,
to reduce patch size and make the patch a bit more readable:
$ git show --stat | grep changed
3 files changed, 83 insertions(+), 43 deletions(-)
After move:
$ git diff HEAD~1 --stat | grep changed
3 files changed, 61 insertions(+), 22 deletions(-)
> {
> struct icmp_ext_hdr *ext_hdr, _ext_hdr;
> struct icmp_ext_echo_iio *iio, _iio;
> - struct icmp_bxm icmp_param;
> + struct net *net = dev_net(skb->dev);
> struct net_device *dev;
> char buff[IFNAMSIZ];
> - struct net *net;
> u16 ident_len;
> u8 status;
>
> - net = dev_net(skb_dst(skb)->dev);
> - /* should there be an ICMP stat for ignored echos? */
> - if (net->ipv4.sysctl_icmp_echo_ignore_all)
> - return true;
> -
> - icmp_param.data.icmph = *icmp_hdr(skb);
> - icmp_param.skb = skb;
> - icmp_param.offset = 0;
> - icmp_param.data_len = skb->len;
> - icmp_param.head_len = sizeof(struct icmphdr);
> -
> - if (icmp_param.data.icmph.type == ICMP_ECHO) {
> - icmp_param.data.icmph.type = ICMP_ECHOREPLY;
> - goto send_reply;
> - }
> if (!net->ipv4.sysctl_icmp_echo_enable_probe)
> - return true;
> + return false;
> +
> /* We currently only support probing interfaces on the proxy node
> * Check to ensure L-bit is set
> */
> - if (!(ntohs(icmp_param.data.icmph.un.echo.sequence) & 1))
> - return true;
> + if (!(ntohs(icmphdr->un.echo.sequence) & 1))
> + return false;
> /* Clear status bits in reply message */
> - icmp_param.data.icmph.un.echo.sequence &= htons(0xFF00);
> - icmp_param.data.icmph.type = ICMP_EXT_ECHOREPLY;
> + icmphdr->un.echo.sequence &= htons(0xFF00);
> + if (icmphdr->type == ICMP_EXT_ECHO)
> + icmphdr->type = ICMP_EXT_ECHOREPLY;
> + else
> + icmphdr->type = ICMPV6_EXT_ECHO_REPLY;
> ext_hdr = skb_header_pointer(skb, 0, sizeof(_ext_hdr), &_ext_hdr);
> /* Size of iio is class_type dependent.
> * Only check header here and assign length based on ctype in the switch statement
> @@ -1087,8 +1068,8 @@ static bool icmp_echo(struct sk_buff *skb)
> goto send_mal_query;
> }
> if (!dev) {
> - icmp_param.data.icmph.code = ICMP_EXT_CODE_NO_IF;
> - goto send_reply;
> + icmphdr->code = ICMP_EXT_CODE_NO_IF;
> + return true;
> }
> /* Fill bits in reply message */
> if (dev->flags & IFF_UP)
> @@ -1098,13 +1079,53 @@ static bool icmp_echo(struct sk_buff *skb)
> if (!list_empty(&rcu_dereference(dev->ip6_ptr)->addr_list))
> status |= ICMP_EXT_ECHOREPLY_IPV6;
> dev_put(dev);
> - icmp_param.data.icmph.un.echo.sequence |= htons(status);
> + icmphdr->un.echo.sequence |= htons(status);
> + return true;
> +send_mal_query:
> + icmphdr->code = ICMP_EXT_CODE_MAL_QUERY;
> + return true;
> +}
Needs EXPORT_SYMBOL_GPL to use it from IPv6 when compiled as a module.
> +
> +/*
> + * Handle ICMP_ECHO ("ping") and ICMP_EXT_ECHO ("PROBE") requests.
> + *
> + * RFC 1122: 3.2.2.6 MUST have an echo server that answers ICMP echo
> + * requests.
> + * RFC 1122: 3.2.2.6 Data received in the ICMP_ECHO request MUST be
> + * included in the reply.
> + * RFC 1812: 4.3.3.6 SHOULD have a config option for silently ignoring
> + * echo requests, MUST have default=NOT.
> + * RFC 8335: 8 MUST have a config option to enable/disable ICMP
> + * Extended Echo Functionality, MUST be disabled by default
> + * See also WRT handling of options once they are done and working.
> + */
> +
> +static bool icmp_echo(struct sk_buff *skb)
> +{
> + struct icmp_bxm icmp_param;
> + struct net *net;
> +
> + net = dev_net(skb_dst(skb)->dev);
> + /* should there be an ICMP stat for ignored echos? */
> + if (net->ipv4.sysctl_icmp_echo_ignore_all)
> + return true;
> +
> + icmp_param.data.icmph = *icmp_hdr(skb);
> + icmp_param.skb = skb;
> + icmp_param.offset = 0;
> + icmp_param.data_len = skb->len;
> + icmp_param.head_len = sizeof(struct icmphdr);
> +
> + if (icmp_param.data.icmph.type == ICMP_ECHO) {
> + icmp_param.data.icmph.type = ICMP_ECHOREPLY;
> + goto send_reply;
> + }
> +
> + if (!icmp_build_probe(skb, &icmp_param.data.icmph))
> + return true;
This control flow can now be simplified:
if (icmp_param.data.icmph.type == ICMP_ECHO)
icmp_param.data.icmph.type = ICMP_ECHOREPLY;
else if !icmp_build_probe(skb, &icmp_param.data.icmph))
return true;
and can remove the send_reply label
> send_reply:
> icmp_reply(&icmp_param, skb);
> return true;
> -send_mal_query:
> - icmp_param.data.icmph.code = ICMP_EXT_CODE_MAL_QUERY;
> - goto send_reply;
> }
>
> /*
> diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
> index e8398ffb5e35..d32a387b36e7 100644
> --- a/net/ipv6/icmp.c
> +++ b/net/ipv6/icmp.c
> @@ -725,6 +725,7 @@ static void icmpv6_echo_reply(struct sk_buff *skb)
> struct ipcm6_cookie ipc6;
> u32 mark = IP6_REPLY_MARK(net, skb->mark);
> bool acast;
> + u8 type;
>
> if (ipv6_addr_is_multicast(&ipv6_hdr(skb)->daddr) &&
> net->ipv6.sysctl.icmpv6_echo_ignore_multicast)
> @@ -740,8 +741,16 @@ static void icmpv6_echo_reply(struct sk_buff *skb)
> !(net->ipv6.sysctl.anycast_src_echo_reply && acast))
> saddr = NULL;
>
> + if (icmph->icmp6_type == ICMPV6_EXT_ECHO_REQUEST) {
> + if (!net->ipv4.sysctl_icmp_echo_enable_probe)
> + return;
> + type = ICMPV6_EXT_ECHO_REPLY;
> + } else {
> + type = ICMPV6_ECHO_REPLY;
> + }
> +
> memcpy(&tmp_hdr, icmph, sizeof(tmp_hdr));
> - tmp_hdr.icmp6_type = ICMPV6_ECHO_REPLY;
> + tmp_hdr.icmp6_type = type;
>
> memset(&fl6, 0, sizeof(fl6));
> if (net->ipv6.sysctl.flowlabel_reflect & FLOWLABEL_REFLECT_ICMPV6_ECHO_REPLIES)
> @@ -752,7 +761,7 @@ static void icmpv6_echo_reply(struct sk_buff *skb)
> if (saddr)
> fl6.saddr = *saddr;
> fl6.flowi6_oif = icmp6_iif(skb);
> - fl6.fl6_icmp_type = ICMPV6_ECHO_REPLY;
> + fl6.fl6_icmp_type = type;
> fl6.flowi6_mark = mark;
> fl6.flowi6_uid = sock_net_uid(net, NULL);
> security_skb_classify_flow(skb, flowi6_to_flowi_common(&fl6));
> @@ -783,13 +792,17 @@ static void icmpv6_echo_reply(struct sk_buff *skb)
>
> msg.skb = skb;
> msg.offset = 0;
> - msg.type = ICMPV6_ECHO_REPLY;
> + msg.type = type;
>
> ipcm6_init_sk(&ipc6, np);
> ipc6.hlimit = ip6_sk_dst_hoplimit(np, &fl6, dst);
> ipc6.tclass = ipv6_get_dsfield(ipv6_hdr(skb));
> ipc6.sockc.mark = mark;
>
> + if (icmph->icmp6_type == ICMPV6_EXT_ECHO_REQUEST)
> + if (!icmp_build_probe(skb, (struct icmphdr *)&tmp_hdr))
> + goto out_dst_release;
> +
> if (ip6_append_data(sk, icmpv6_getfrag, &msg,
> skb->len + sizeof(struct icmp6hdr),
> sizeof(struct icmp6hdr), &ipc6, &fl6,
> @@ -912,6 +925,11 @@ static int icmpv6_rcv(struct sk_buff *skb)
> icmpv6_echo_reply(skb);
> break;
>
> + case ICMPV6_EXT_ECHO_REQUEST:
> + if (!net->ipv6.sysctl.icmpv6_echo_ignore_all)
> + icmpv6_echo_reply(skb);
> + break;
> +
This can be a one line change to add the case to the existing case above.
But either way, you might prefer this.
> case ICMPV6_ECHO_REPLY:
> success = ping_rcv(skb);
> break;
> --
> 2.32.0
>
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