On Thu, Jul 10, 2025 at 09:07:59AM -0700, Alexei Starovoitov wrote:
> On Thu, Jul 10, 2025 at 3:26 AM Mahe Tardy <mahe.tardy@xxxxxxxxx> 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
> > (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@xxxxxxxxx>
> > ---
> > net/core/filter.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++-
> > 1 file changed, 60 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index ab456bf1056e..9215f79e7690 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -85,6 +85,8 @@
> > #include <linux/un.h>
> > #include <net/xdp_sock_drv.h>
> > #include <net/inet_dscp.h>
> > +#include <linux/icmp.h>
> > +#include <net/icmp.h>
> >
> > #include "dev.h"
> >
> > @@ -12140,6 +12142,53 @@ __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) {
> > + kfree_skb(nskb);
> > + return -EHOSTUNREACH;
> > + }
> > +
> > + icmpv6_send(nskb, ICMPV6_DEST_UNREACH, code, 0);
> > + kfree_skb(nskb);
> > + break;
> > +#endif
> > + default:
> > + return -EPROTONOSUPPORT;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > __bpf_kfunc_end_defs();
> >
> > int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
> > @@ -12177,6 +12226,10 @@ BTF_KFUNCS_START(bpf_kfunc_check_set_sock_ops)
> > BTF_ID_FLAGS(func, bpf_sock_ops_enable_tx_tstamp, KF_TRUSTED_ARGS)
> > BTF_KFUNCS_END(bpf_kfunc_check_set_sock_ops)
> >
> > +BTF_KFUNCS_START(bpf_kfunc_check_set_icmp_send_unreach)
> > +BTF_ID_FLAGS(func, bpf_icmp_send_unreach, KF_TRUSTED_ARGS)
> > +BTF_KFUNCS_END(bpf_kfunc_check_set_icmp_send_unreach)
> > +
> > static const struct btf_kfunc_id_set bpf_kfunc_set_skb = {
> > .owner = THIS_MODULE,
> > .set = &bpf_kfunc_check_set_skb,
> > @@ -12202,6 +12255,11 @@ static const struct btf_kfunc_id_set bpf_kfunc_set_sock_ops = {
> > .set = &bpf_kfunc_check_set_sock_ops,
> > };
> >
> > +static const struct btf_kfunc_id_set bpf_kfunc_set_icmp_send_unreach = {
> > + .owner = THIS_MODULE,
> > + .set = &bpf_kfunc_check_set_icmp_send_unreach,
> > +};
> > +
> > static int __init bpf_kfunc_init(void)
> > {
> > int ret;
> > @@ -12221,7 +12279,8 @@ static int __init bpf_kfunc_init(void)
> > ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
> > &bpf_kfunc_set_sock_addr);
> > ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &bpf_kfunc_set_tcp_reqsk);
> > - return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SOCK_OPS, &bpf_kfunc_set_sock_ops);
> > + ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SOCK_OPS, &bpf_kfunc_set_sock_ops);
> > + return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SKB, &bpf_kfunc_set_icmp_send_unreach);
>
> Does it have to be restricted to BPF_PROG_TYPE_CGROUP_SKB ?
> Can it be a part of bpf_kfunc_set_skb[] and used more generally ?
