From: Mahe Tardy <mahe.tardy@gmail•com>
To: Martin KaFai Lau <martin.lau@linux•dev>
Cc: alexei.starovoitov@gmail•com, andrii@kernel•org, ast@kernel•org,
bpf@vger•kernel.org, coreteam@netfilter•org,
daniel@iogearbox•net, fw@strlen•de, john.fastabend@gmail•com,
netdev@vger•kernel.org, netfilter-devel@vger•kernel.org,
oe-kbuild-all@lists•linux.dev, pablo@netfilter•org,
lkp@intel•com
Subject: Re: [PATCH bpf-next v3 3/4] bpf: add bpf_icmp_send_unreach cgroup_skb kfunc
Date: Tue, 29 Jul 2025 12:06:26 +0200 [thread overview]
Message-ID: <aIidIq2EM--Ugp6f@gmail.com> (raw)
In-Reply-To: <b3f25e61-7b0c-4576-baae-9b498c3b8748@linux.dev>
On Mon, Jul 28, 2025 at 06:05:26PM -0700, Martin KaFai Lau wrote:
> On 7/28/25 2:43 AM, Mahe Tardy wrote:
> > This is needed in the context of Tetragon to provide improved feedback
> > (in contrast to just dropping packets) to east-west traffic when blocked
> > by policies using cgroup_skb programs.
> >
> > This reuse concepts from netfilter reject target codepath with the
> > differences that:
> > * Packets are cloned since the BPF user can still return SK_PASS from
> > the cgroup_skb progs and the current skb need to stay untouched
>
> This needs more details. Which field(s) of the skb are changed by the kfunc,
> the skb_dst_set in ip[6]_route_reply_fetch_dst() and/or the code path in the
> icmp[v6]_send() ?
Okay I can add that: "ip[6]_route_reply_fetch_dst set the dst of the skb
by using the saddr as a daddr and routing it", I don't think
icmp[v6]_send touches the skb?
>
> > (cgroup_skb hooks only allow read-only skb payload).
> > * Since cgroup_skb programs are called late in the stack, checksums do
> > not need to be computed or verified, and IPv4 fragmentation does not
> > need to be checked (ip_local_deliver should take care of that
> > earlier).
> >
> > Signed-off-by: Mahe Tardy <mahe.tardy@gmail•com>
> > ---
> > net/core/filter.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 61 insertions(+)
> >
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 7a72f766aacf..050872324575 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -85,6 +85,10 @@
> > #include <linux/un.h>
> > #include <net/xdp_sock_drv.h>
> > #include <net/inet_dscp.h>
> > +#include <linux/icmp.h>
> > +#include <net/icmp.h>
> > +#include <net/route.h>
> > +#include <net/ip6_route.h>
> >
> > #include "dev.h"
> >
> > @@ -12148,6 +12152,53 @@ __bpf_kfunc int bpf_sock_ops_enable_tx_tstamp(struct bpf_sock_ops_kern *skops,
> > return 0;
> > }
> >
> > +__bpf_kfunc int bpf_icmp_send_unreach(struct __sk_buff *__skb, int code)
> > +{
> > + struct sk_buff *skb = (struct sk_buff *)__skb;
> > + struct sk_buff *nskb;
> > +
> > + switch (skb->protocol) {
> > + case htons(ETH_P_IP):
> > + if (code < 0 || code > NR_ICMP_UNREACH)
> > + return -EINVAL;
> > +
> > + nskb = skb_clone(skb, GFP_ATOMIC);
> > + if (!nskb)
> > + return -ENOMEM;
> > +
> > + if (ip_route_reply_fetch_dst(nskb) < 0) {
> > + kfree_skb(nskb);
> > + return -EHOSTUNREACH;
> > + }
> > +
> > + icmp_send(nskb, ICMP_DEST_UNREACH, code, 0);
> > + kfree_skb(nskb);
> > + break;
> > +#if IS_ENABLED(CONFIG_IPV6)
> > + case htons(ETH_P_IPV6):
> > + if (code < 0 || code > ICMPV6_REJECT_ROUTE)
> > + return -EINVAL;
> > +
> > + nskb = skb_clone(skb, GFP_ATOMIC);
> > + if (!nskb)
> > + return -ENOMEM;
> > +
> > + if (ip6_route_reply_fetch_dst(nskb) < 0) {
>
> From a very quick look at icmpv6_send(), it does its own route lookup. I
> haven't looked at the v4 yet.
>
> I am likely missing some details. Can you explain why it needs to do a
> lookup before calling icmpv6_send()?
From my understanding, I need to do this to invert the daddr with the
saddr to send the unreach message back to the sender.
>
> > + kfree_skb(nskb);
> > + return -EHOSTUNREACH;
> > + }
> > +
> > + icmpv6_send(nskb, ICMPV6_DEST_UNREACH, code, 0);
> > + kfree_skb(nskb);
> > + break;
> > +#endif
> > + default:
> > + return -EPROTONOSUPPORT;
> > + }
> > +
> > + return SK_DROP;
> > +}
> > +
next prev parent reply other threads:[~2025-07-29 10:06 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAADnVQKq_-=N7eJoup6AqFngoocT+D02NF0md_3mi2Vcrw09nQ@mail.gmail.com>
2025-07-25 18:53 ` [PATCH bpf-next v1 0/4] bpf: add icmp_send_unreach kfunc Mahe Tardy
2025-07-25 18:53 ` [PATCH bpf-next v2 1/4] net: move netfilter nf_reject_fill_skb_dst to core ipv4 Mahe Tardy
2025-07-25 18:53 ` [PATCH bpf-next v2 2/4] net: move netfilter nf_reject6_fill_skb_dst to core ipv6 Mahe Tardy
2025-07-25 18:53 ` [PATCH bpf-next v2 3/4] bpf: add bpf_icmp_send_unreach cgroup_skb kfunc Mahe Tardy
2025-07-27 1:49 ` kernel test robot
2025-07-28 9:43 ` [PATCH bpf-next v3 0/4] bpf: add icmp_send_unreach kfunc Mahe Tardy
2025-07-28 9:43 ` [PATCH bpf-next v3 1/4] net: move netfilter nf_reject_fill_skb_dst to core ipv4 Mahe Tardy
2025-07-28 9:43 ` [PATCH bpf-next v3 2/4] net: move netfilter nf_reject6_fill_skb_dst to core ipv6 Mahe Tardy
2025-07-28 9:43 ` [PATCH bpf-next v3 3/4] bpf: add bpf_icmp_send_unreach cgroup_skb kfunc Mahe Tardy
2025-07-28 20:10 ` kernel test robot
2025-07-29 1:05 ` Martin KaFai Lau
2025-07-29 10:06 ` Mahe Tardy [this message]
2025-07-29 23:13 ` Martin KaFai Lau
2025-07-28 9:43 ` [PATCH bpf-next v3 4/4] selftests/bpf: add icmp_send_unreach kfunc tests Mahe Tardy
2025-07-28 15:40 ` Yonghong Song
2025-07-28 15:59 ` Mahe Tardy
2025-07-29 1:18 ` Martin KaFai Lau
2025-07-29 9:09 ` Mahe Tardy
2025-07-29 23:27 ` Martin KaFai Lau
2025-07-30 0:01 ` Martin KaFai Lau
2025-07-30 0:32 ` Martin KaFai Lau
2025-08-05 23:26 ` Jordan Rife
2025-07-29 1:21 ` [PATCH bpf-next v3 0/4] bpf: add icmp_send_unreach kfunc Martin KaFai Lau
2025-07-29 9:53 ` Mahe Tardy
2025-07-30 1:54 ` Martin KaFai Lau
2025-08-01 18:50 ` Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 0/6] " Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 1/6] net: move netfilter nf_reject_fill_skb_dst to core ipv4 Mahe Tardy
2026-04-20 11:36 ` bot+bpf-ci
2026-04-20 13:04 ` Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 2/6] net: move netfilter nf_reject6_fill_skb_dst to core ipv6 Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 3/6] bpf: add bpf_icmp_send_unreach kfunc Mahe Tardy
2026-04-20 11:36 ` bot+bpf-ci
2026-04-20 13:07 ` Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 4/6] selftests/bpf: add icmp_send_unreach kfunc tests Mahe Tardy
2026-04-20 11:36 ` bot+bpf-ci
2026-04-20 13:08 ` Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 5/6] selftests/bpf: add icmp_send_unreach kfunc IPv6 tests Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 6/6] selftests/bpf: add icmp_send_unreach_recursion test Mahe Tardy
2025-07-25 18:53 ` [PATCH bpf-next v2 4/4] selftests/bpf: add icmp_send_unreach kfunc tests Mahe Tardy
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