[PATCH bpf-next v2 5/8] bpf: net: ipv6: Add bpf_ipv6_frag_rcv() kfunc
From: Daniel Xu
Date: Mon Feb 27 2023 - 14:52:45 EST
This helper is used to defragment IPv6 packets. Similar to the previous
bpf_ip_check_defrag() kfunc, this kfunc:
* Returns 0 on defrag + skb update success
* Returns < 0 on error
* Takes care to ensure ctx (skb) remains valid no matter what the
underlying call to _ipv6_frag_rcv() does
* Is only callable from TC clsact progs
Please see bpf_ip_check_defrag() commit for more details / suggestions.
Signed-off-by: Daniel Xu <dxu@xxxxxxxxx>
---
include/net/ipv6_frag.h | 1 +
include/net/transp_v6.h | 1 +
net/ipv6/Makefile | 1 +
net/ipv6/af_inet6.c | 4 ++
net/ipv6/reassembly_bpf.c | 143 ++++++++++++++++++++++++++++++++++++++
5 files changed, 150 insertions(+)
create mode 100644 net/ipv6/reassembly_bpf.c
diff --git a/include/net/ipv6_frag.h b/include/net/ipv6_frag.h
index 7321ffe3a108..cf4763cd3886 100644
--- a/include/net/ipv6_frag.h
+++ b/include/net/ipv6_frag.h
@@ -15,6 +15,7 @@ enum ip6_defrag_users {
__IP6_DEFRAG_CONNTRACK_OUT = IP6_DEFRAG_CONNTRACK_OUT + USHRT_MAX,
IP6_DEFRAG_CONNTRACK_BRIDGE_IN,
__IP6_DEFRAG_CONNTRACK_BRIDGE_IN = IP6_DEFRAG_CONNTRACK_BRIDGE_IN + USHRT_MAX,
+ IP6_DEFRAG_BPF,
};
/*
diff --git a/include/net/transp_v6.h b/include/net/transp_v6.h
index d27b1caf3753..244123a74349 100644
--- a/include/net/transp_v6.h
+++ b/include/net/transp_v6.h
@@ -20,6 +20,7 @@ int ipv6_exthdrs_init(void);
void ipv6_exthdrs_exit(void);
int ipv6_frag_init(void);
void ipv6_frag_exit(void);
+int register_ipv6_reassembly_bpf(void);
/* transport protocols */
int pingv6_init(void);
diff --git a/net/ipv6/Makefile b/net/ipv6/Makefile
index 3036a45e8a1e..6e90ff1d20c0 100644
--- a/net/ipv6/Makefile
+++ b/net/ipv6/Makefile
@@ -26,6 +26,7 @@ ipv6-$(CONFIG_IPV6_SEG6_LWTUNNEL) += seg6_iptunnel.o seg6_local.o
ipv6-$(CONFIG_IPV6_SEG6_HMAC) += seg6_hmac.o
ipv6-$(CONFIG_IPV6_RPL_LWTUNNEL) += rpl_iptunnel.o
ipv6-$(CONFIG_IPV6_IOAM6_LWTUNNEL) += ioam6_iptunnel.o
+ipv6-$(CONFIG_DEBUG_INFO_BTF) += reassembly_bpf.o
obj-$(CONFIG_INET6_AH) += ah6.o
obj-$(CONFIG_INET6_ESP) += esp6.o
diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index 38689bedfce7..39663de75fbd 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -1174,6 +1174,10 @@ static int __init inet6_init(void)
if (err)
goto ipv6_frag_fail;
+ err = register_ipv6_reassembly_bpf();
+ if (err)
+ goto ipv6_frag_fail;
+
/* Init v6 transport protocols. */
err = udpv6_init();
if (err)
diff --git a/net/ipv6/reassembly_bpf.c b/net/ipv6/reassembly_bpf.c
new file mode 100644
index 000000000000..c6c804d4f636
--- /dev/null
+++ b/net/ipv6/reassembly_bpf.c
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Unstable ipv6 fragmentation helpers for TC-BPF hook
+ *
+ * These are called from SCHED_CLS BPF programs. Note that it is allowed to
+ * break compatibility for these functions since the interface they are exposed
+ * through to BPF programs is explicitly unstable.
+ */
+
+#include <linux/bpf.h>
+#include <linux/btf_ids.h>
+#include <linux/filter.h>
+#include <linux/netdevice.h>
+#include <net/ipv6.h>
+#include <net/ipv6_frag.h>
+#include <net/ipv6_stubs.h>
+
+static int set_dst(struct sk_buff *skb, struct net *net)
+{
+ const struct ipv6hdr *ip6h = ipv6_hdr(skb);
+ struct dst_entry *dst;
+
+ struct flowi6 fl6 = {
+ .flowi6_flags = FLOWI_FLAG_ANYSRC,
+ .flowi6_mark = skb->mark,
+ .flowlabel = ip6_flowinfo(ip6h),
+ .flowi6_iif = skb->skb_iif,
+ .flowi6_proto = ip6h->nexthdr,
+ .daddr = ip6h->daddr,
+ .saddr = ip6h->saddr,
+ };
+
+ dst = ipv6_stub->ipv6_dst_lookup_flow(net, NULL, &fl6, NULL);
+ if (IS_ERR(dst))
+ return PTR_ERR(dst);
+
+ skb_dst_set(skb, dst);
+
+ return 0;
+}
+
+__diag_push();
+__diag_ignore_all("-Wmissing-prototypes",
+ "Global functions as their definitions will be in reassembly BTF");
+
+/* bpf_ipv6_frag_rcv - Defragment an ipv6 packet
+ *
+ * This helper takes an skb as input. If this skb successfully reassembles
+ * the original packet, the skb is updated to contain the original, reassembled
+ * packet.
+ *
+ * Otherwise (on error or incomplete reassembly), the input skb remains
+ * unmodified.
+ *
+ * Parameters:
+ * @ctx - Pointer to program context (skb)
+ * @netns - Child network namespace id. If value is a negative signed
+ * 32-bit integer, the netns of the device in the skb is used.
+ *
+ * Return:
+ * 0 on successfully reassembly or non-fragmented packet. Negative value on
+ * error or incomplete reassembly.
+ */
+int bpf_ipv6_frag_rcv(struct __sk_buff *ctx, u64 netns)
+{
+ struct sk_buff *skb = (struct sk_buff *)ctx;
+ struct sk_buff *skb_cpy;
+ struct net *caller_net;
+ unsigned int foff;
+ struct net *net;
+ int mac_len;
+ void *mac;
+ int err;
+
+ if (unlikely(!((s32)netns < 0 || netns <= S32_MAX)))
+ return -EINVAL;
+
+ caller_net = skb->dev ? dev_net(skb->dev) : sock_net(skb->sk);
+ if ((s32)netns < 0) {
+ net = caller_net;
+ } else {
+ net = get_net_ns_by_id(caller_net, netns);
+ if (unlikely(!net))
+ return -EINVAL;
+ }
+
+ err = set_dst(skb, net);
+ if (err < 0)
+ return err;
+
+ mac_len = skb->mac_len;
+ skb_cpy = skb_copy(skb, GFP_ATOMIC);
+ if (!skb_cpy)
+ return -ENOMEM;
+
+ /* _ipv6_frag_rcv() expects skb->transport_header to be set to start of
+ * the frag header and nhoff to be set.
+ */
+ err = ipv6_find_hdr(skb_cpy, &foff, NEXTHDR_FRAGMENT, NULL, NULL);
+ if (err < 0)
+ return err;
+ skb_set_transport_header(skb_cpy, foff);
+ IP6CB(skb_cpy)->nhoff = offsetof(struct ipv6hdr, nexthdr);
+
+ /* inet6_protocol handlers return >0 on success, 0 on out of band
+ * consumption, <0 on error. We never expect to see 0 here.
+ */
+ err = _ipv6_frag_rcv(net, skb_cpy, IP6_DEFRAG_BPF);
+ if (err < 0)
+ return err;
+ else if (err == 0)
+ return -EINVAL;
+
+ skb_morph(skb, skb_cpy);
+ kfree_skb(skb_cpy);
+
+ /* _ipv6_frag_rcv() does not maintain mac header, so push empty header
+ * in so prog sees the correct layout. The empty mac header will be
+ * later pulled from cls_bpf.
+ */
+ skb->mac_len = mac_len;
+ mac = skb_push(skb, mac_len);
+ memset(mac, 0, mac_len);
+ bpf_compute_data_pointers(skb);
+
+ return 0;
+}
+
+__diag_pop()
+
+BTF_SET8_START(ipv6_reassembly_kfunc_set)
+BTF_ID_FLAGS(func, bpf_ipv6_frag_rcv, KF_CHANGES_PKT)
+BTF_SET8_END(ipv6_reassembly_kfunc_set)
+
+static const struct btf_kfunc_id_set ipv6_reassembly_bpf_kfunc_set = {
+ .owner = THIS_MODULE,
+ .set = &ipv6_reassembly_kfunc_set,
+};
+
+int register_ipv6_reassembly_bpf(void)
+{
+ return register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS,
+ &ipv6_reassembly_bpf_kfunc_set);
+}
--
2.39.1