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Message-ID: <CAL+tcoDeXXh+zcRk4PHnUk8ELnx=CE2pcCqs7sFm0y9aK-Eehg@mail.gmail.com>
Date: Thu, 11 Apr 2024 14:46:35 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Peilin He <peilinhe2020@....com>
Cc: davem@...emloft.net, dsahern@...nel.org, edumazet@...gle.com,
fan.yu9@....com.cn, he.peilin@....com.cn, jiang.xuexin@....com.cn,
kuba@...nel.org, linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org, liu.chun2@....com.cn, mhiramat@...nel.org,
netdev@...r.kernel.org, qiu.yutan@....com.cn, rostedt@...dmis.org,
xu.xin16@....com.cn, yang.yang29@....com.cn, zhang.yunkai@....com.cn
Subject: Re: Re: Re: Subject: [PATCH net-next v4] net/ipv4: add tracepoint for icmp_send
On Thu, Apr 11, 2024 at 12:57 PM Peilin He <peilinhe2020@....com> wrote:
>
> >> >[...]
> >> >> >I think my understanding based on what Eric depicted differs from you:
> >> >> >we're supposed to filter out those many invalid cases and only trace
> >> >> >the valid action of sending a icmp, so where to add a new tracepoint
> >> >> >is important instead of adding more checks in the tracepoint itself.
> >> >> >Please refer to what trace_tcp_retransmit_skb() does :)
> >> >> >
> >> >> >Thanks,
> >> >> >Jason
> >> >> Okay, thank you for your suggestion. In order to avoid filtering out
> >> >> those many invalid cases and only tracing the valid action of sending
> >> >> a icmp, the next patch will add udd_fail_no_port trancepoint to the
> >> >> include/trace/events/udp.h. This will solve the problem you mentioned
> >> >> very well. At this point, only UDP protocol exceptions will be tracked,
> >> >> without the need to track them in icmp_send.
> >> >
> >> >I'm not against what you did (tracing all the icmp_send() for UDP) in
> >> >your original patch. I was suggesting that you could put
> >> >trace_icmp_send() in the right place, then you don't have to check the
> >> >possible error condition (like if the skb->head is valid or not, ...)
> >> >in your trace function.
> >> >
> >> >One example that can avoid various checks existing in the
> >> >__icmp_send() function:
> >> >diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
> >> >index e63a3bf99617..2c9f7364de45 100644
> >> >--- a/net/ipv4/icmp.c
> >> >+++ b/net/ipv4/icmp.c
> >> >@@ -767,6 +767,7 @@ void __icmp_send(struct sk_buff *skb_in, int type,
> >> >int code, __be32 info,
> >> > if (!fl4.saddr)
> >> > fl4.saddr = htonl(INADDR_DUMMY);
> >> >
> >> >+ trace_icmp_send(skb_in, type, code);
> >> > icmp_push_reply(sk, &icmp_param, &fl4, &ipc, &rt);
> >> > ende
> >> > ip_rt_put(rt);
> >> >
> >> >If we go here, it means we are ready to send the ICMP skb because
> >> >we're done extracting the right information in the 'struct sk_buff
> >> >skb_in'. Simpler and easier, right?
> >> >
> >> >Thanks,
> >> >Jason
> >>
> >> I may not fully agree with this viewpoint. When trace_icmp_send is placed
> >> in this position, it cannot guarantee that all skbs in icmp are UDP protocols
> >> (UDP needs to be distinguished based on the proto_4!=IPPROTO_UDP condition),
> >> nor can it guarantee the legitimacy of udphdr (*uh legitimacy check is required).
> >
> >Of course, the UDP test statement is absolutely needed! Eric
> >previously pointed this out in the V1 patch thread. I'm not referring
> >to this one but like skb->head check something like this which exists
> >in __icmp_send() function. You can see there are so many checks in it
> >before sending.
> >
> >So only keeping the UDP check is enough, I think.
>
> The __icmp_send function only checks the IP header, but does not check
> the UDP header, as shown in the following code snippet:
>
> if ((u8 *)iph < skb_in->head ||
> (skb_network_header(skb_in) + sizeof(*iph)) >
> skb_tail_pointer(skb_in))
> goto out;
>
> There is no problem with the IP header check, which does not mean that
> the UDP header is correct. Therefore, I believe that it is essential to
> include a legitimacy judgment for the UDP header.
>
> Here is an explanation of this code:
> Firstly, the UDP header (*uh) is extracted from the skb.
> Then, if the current protocol of the skb is not UDP, or if the address of
> uh is outside the range of the skb, the source port and destination port
> will not be resolved, and 0 will be filled in directly.Otherwise,
> the source port and destination port of the UDP header will be resolved.
>
> + struct udphdr *uh = udp_hdr(skb);
> + if (proto_4 != IPPROTO_UDP || (u8 *)uh < skb->head ||
> + (u8 *)uh + sizeof(struct udphdr) > skb_tail_pointer(skb)) {
>From the beginning, I always agree with the UDP check. I was saying if
you can put the trace_icmp_send() just before icmp_push_reply()[1],
you could avoid those kinds of checks.
As I said in the previous email, "only keeping the UDP check is
enough". So you are right.
[1]
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index e63a3bf99617..2c9f7364de45 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -767,6 +767,7 @@ void __icmp_send(struct sk_buff *skb_in, int type,
int code, __be32 info,
if (!fl4.saddr)
fl4.saddr = htonl(INADDR_DUMMY);
+ trace_icmp_send(skb_in, type, code);
icmp_push_reply(sk, &icmp_param, &fl4, &ipc, &rt);
ende:
ip_rt_put(rt);
If we're doing this, trace_icmp_send() can reflect the real action of
sending an ICMP like trace_tcp_retransmit_skb(). Or else, the trace
could print some messages but no real ICMP is sent (see those error
checks). WDYT?
Thanks,
Jason
>
> With best wishes
> Peilin He
>
> >Thanks,
> >Jason
> >
> >>
> >> With best wishes
> >> Peilin He
> >>
> >> >>
> >> >> >> 2.Target this patch for net-next.
> >> >> >>
> >> >> >> v2->v3:
> >> >> >> Some fixes according to
> >> >> >> https://lore.kernel.org/all/20240319102549.7f7f6f53@gandalf.local.home/
> >> >> >> 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=3DsZtRnKRu_tnUwqHuFQTJvJsv=
> >> >> >-nz1xPDw@...l.gmail.com/
> >> >> >> 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@....com.cn>
> >> >> >> Reviewed-by: xu xin <xu.xin16@....com.cn>
> >> >> >> Reviewed-by: Yunkai Zhang <zhang.yunkai@....com.cn>
> >> >> >> Cc: Yang Yang <yang.yang29@....com.cn>
> >> >> >> Cc: Liu Chun <liu.chun2@....com.cn>
> >> >> >> Cc: Xuexin Jiang <jiang.xuexin@....com.cn>
> >> >> >> ---
> >> >> >> include/trace/events/icmp.h | 65 +++++++++++++++++++++++++++++++++++++
> >> >> >> net/ipv4/icmp.c | 4 +++
> >> >> >> 2 files changed, 69 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..7d5190f48a28
> >> >> >> --- /dev/null
> >> >> >> +++ b/include/trace/events/icmp.h
> >> >> >> @@ -0,0 +1,65 @@
> >> >> >> +/* 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 =3D ip_hdr(skb);
> >> >> >> + int proto_4 =3D iph->protocol;
> >> >> >> + __be32 *p32;
> >> >> >> +
> >> >> >> + __entry->skbaddr =3D skb;
> >> >> >> + __entry->type =3D type;
> >> >> >> + __entry->code =3D code;
> >> >> >> +
> >> >> >> + struct udphdr *uh =3D udp_hdr(skb);
> >> >> >> + if (proto_4 !=3D IPPROTO_UDP || (u8 *)uh < skb->h=
> >> >> >ead ||
> >> >> >> + (u8 *)uh + sizeof(struct udphdr) > skb_ta=
> >> >> >il_pointer(skb)) {
> >> >> >> + __entry->sport =3D 0;
> >> >> >> + __entry->dport =3D 0;
> >> >> >> + __entry->ulen =3D 0;
> >> >> >> + } else {
> >> >> >> + __entry->sport =3D ntohs(uh->source);
> >> >> >> + __entry->dport =3D ntohs(uh->dest);
> >> >> >> + __entry->ulen =3D ntohs(uh->len);
> >> >> >> + }
> >> >> >> +
> >> >> >> + p32 =3D (__be32 *) __entry->saddr;
> >> >> >> + *p32 =3D iph->saddr;
> >> >> >> +
> >> >> >> + p32 =3D (__be32 *) __entry->daddr;
> >> >> >> + *p32 =3D iph->daddr;
> >> >> >> + ),
> >> >> >> +
> >> >> >> + TP_printk("icmp_send: type=3D%d, code=3D%d. >From %pI4:%u =
> >> >> >to %pI4:%u ulen=3D%d skbaddr=3D%p",
> >> >> >> + __entry->type, __entry->code,
> >> >> >> + __entry->saddr, __entry->sport, __entry->daddr,
> >> >> >> + __entry->dport, __entry->ulen, __entry->skbaddr)
> >> >> >> +);
> >> >> >> +
> >> >> >> +#endif /* _TRACE_ICMP_H */
> >> >> >> +
> >> >> >> +/* This part must be outside protection */
> >> >> >> +#include <trace/define_trace.h>
> >> >> >> \ No newline at end of file
> >> >> >> diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
> >> >> >> index 8cebb476b3ab..224551d75c02 100644
> >> >> >> --- a/net/ipv4/icmp.c
> >> >> >> +++ b/net/ipv4/icmp.c
> >> >> >> @@ -92,6 +92,8 @@
> >> >> >> #include <net/inet_common.h>
> >> >> >> #include <net/ip_fib.h>
> >> >> >> #include <net/l3mdev.h>
> >> >> >> +#define CREATE_TRACE_POINTS
> >> >> >> +#include <trace/events/icmp.h>
> >> >> >>
> >> >> >> /*
> >> >> >> * Build xmit assembly blocks
> >> >> >> @@ -672,6 +674,8 @@ void __icmp_send(struct sk_buff *skb_in, int type, in=
> >> >> >t code, __be32 info,
> >> >> >> }
> >> >> >> }
> >> >> >>
> >> >> >> + trace_icmp_send(skb_in, type, code);
> >> >> >> +
> >> >> >> /* Needed by both icmp_global_allow and icmp_xmit_lock */
> >> >> >> local_bh_disable();
> >> >> >>
> >> >> >> --
> >> >> >> 2.25.1
>
>
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