Re: [PATCH v3 resend] net/ipv4: add tracepoint for icmp_send

[Eric Dumazet]

On Thu, Mar 21, 2024 at 4:09 AM <xu.xin16@xxxxxxxxxx> wrote:
>
> From: he peilin <he.peilin@xxxxxxxxxx>
>
> Introduce a tracepoint for icmp_send, which can help users to get more
> detail information conveniently when icmp abnormal events happen.
>
> 1. Giving an usecase example:
> =============================
> When an application experiences packet loss due to an unreachable UDP
> destination port, the kernel will send an exception message through the
> icmp_send function. By adding a trace point for icmp_send, developers or
> system administrators can obtain detailed information about the UDP
> packet loss, including the type, code, source address, destination address,
> source port, and destination port. This facilitates the trouble-shooting
> of UDP packet loss issues especially for those network-service
> applications.
>
> 2. Operation Instructions:
> ==========================
> Switch to the tracing directory.
>         cd /sys/kernel/tracing
> Filter for destination port unreachable.
>         echo "type==3 && code==3" > events/icmp/icmp_send/filter
> Enable trace event.
>         echo 1 > events/icmp/icmp_send/enable
>
> 3. Result View:
> ================
>  udp_client_erro-11370   [002] ...s.12   124.728002:
>  icmp_send: icmp_send: type=3, code=3.
>  From 127.0.0.1:41895 to 127.0.0.1:6666 ulen=23
>  skbaddr=00000000589b167a
>
> Changelog
> ---------
> v2->v3:
> Some fixes according to
> https://lore.kernel.org/all/20240319102549.7f7f6f53@xxxxxxxxxxxxxxxxxx/
> 1. Change the tracking directory to/sys/kernel/tracking.
> 2. Adjust the layout of the TP-STRUCT_entry parameter structure.
>
> v1->v2:
> Some fixes according to
> https://lore.kernel.org/all/CANn89iL-y9e_VFpdw=sZtRnKRu_tnUwqHuFQTJvJsv-nz1xPDw@xxxxxxxxxxxxxx/
> 1. adjust the trace_icmp_send() to more protocols than UDP.
> 2. move the calling of trace_icmp_send after sanity checks
> in __icmp_send().
>
> Signed-off-by: Peilin He<he.peilin@xxxxxxxxxx>
> Reviewed-by: xu xin <xu.xin16@xxxxxxxxxx>
> Reviewed-by: Yunkai Zhang <zhang.yunkai@xxxxxxxxxx>
> Cc: Yang Yang <yang.yang29@xxxxxxxxxx>
> Cc: Liu Chun <liu.chun2@xxxxxxxxxx>
> Cc: Xuexin Jiang <jiang.xuexin@xxxxxxxxxx>
> ---
>  include/trace/events/icmp.h | 64 +++++++++++++++++++++++++++++++++++++
>  net/ipv4/icmp.c             |  4 +++
>  2 files changed, 68 insertions(+)
>  create mode 100644 include/trace/events/icmp.h
>
> diff --git a/include/trace/events/icmp.h b/include/trace/events/icmp.h
> new file mode 100644
> index 000000000000..2098d4b1b12e
> --- /dev/null
> +++ b/include/trace/events/icmp.h
> @@ -0,0 +1,64 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM icmp
> +
> +#if !defined(_TRACE_ICMP_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_ICMP_H
> +
> +#include <linux/icmp.h>
> +#include <linux/tracepoint.h>
> +
> +TRACE_EVENT(icmp_send,
> +
> +               TP_PROTO(const struct sk_buff *skb, int type, int code),
> +
> +               TP_ARGS(skb, type, code),
> +
> +               TP_STRUCT__entry(
> +                       __field(const void *, skbaddr)
> +                       __field(int, type)
> +                       __field(int, code)
> +                       __array(__u8, saddr, 4)
> +                       __array(__u8, daddr, 4)
> +                       __field(__u16, sport)
> +                       __field(__u16, dport)
> +                       __field(unsigned short, ulen)
> +               ),
> +
> +               TP_fast_assign(
> +                       struct iphdr *iph = ip_hdr(skb);
> +                       int proto_4 = iph->protocol;
> +                       __be32 *p32;
> +
> +                       __entry->skbaddr = skb;
> +                       __entry->type = type;
> +                       __entry->code = code;
> +
> +                       if (proto_4 == IPPROTO_UDP) {
> +                               struct udphdr *uh = udp_hdr(skb);
> +                               __entry->sport = ntohs(uh->source);
> +                               __entry->dport = ntohs(uh->dest);
> +                               __entry->ulen = ntohs(uh->len);

This is completely bogus.

Adding tracepoints is ok if there are no side effects like bugs :/

At this point there is no guarantee the UDP header is complete/present
in skb->head

Look at the existing checks between lines 619 and 623

Then audit all icmp_send() callers, and ask yourself if UDP packets
can not be malicious (like with a truncated UDP header)