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Add sample usage for BPF_PROG_TYPE_NETFILTER
Signed-off-by: David Wang <[email protected]>
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@@ -11,4 +11,7 @@ typedef __u64 u64; | |
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| typedef s64 ktime_t; | ||
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| typedef u32 uint32_t; | ||
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| #endif /* __VMLINUX_TYPES_H__ */ | ||
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| # SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) | ||
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| USER_TARGETS := netfilter_ip4_blocklist | ||
| BPF_TARGETS := netfilter_ip4_blocklist.bpf | ||
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| LIB_DIR = ../lib | ||
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| include $(LIB_DIR)/common.mk |
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| # Introduction | ||
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| BPF_PROG_TYPE_NETFILTER was introduced in 6.4, now with a new kernel, a bpf program could attach to netfilter hooks and handles package in a similiar way as iptables/nftables. By now, 6.5.0, there is no bpf kfunc implemented yet for DNAT/SNAT, and the only thing a bpf program can do is to decide whether to DROP the package or not. | ||
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| * netfilter_ip4_blocklist.c/netfilter_ip4_blocklist.bpf.c | ||
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| This sample code implements a simple ipv4 blocklist. | ||
| The bpf program drops package if destination ip address hits a match in the map of type BPF_MAP_TYPE_LPM_TRIE, | ||
| The userspace code would load the bpf program, attach it to netfilter's FORWARD/OUTPUT hook, and then write ip patterns into the bpf map. | ||
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| # TODO | ||
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| This sample hard-codes ip address to be blocked, just for demonstration. | ||
| It would be better to break the userspace program into two parts: | ||
| * init program | ||
| Loads bpf program and pin bpf program and map into somewhere under /sys/fs/bpf | ||
| * interactive program | ||
| add/delete/query ip blocklist via bpf map under /sys/fs/bpf | ||
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| // SPDX-License-Identifier: GPL-2.0 | ||
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| #include "vmlinux_local.h" | ||
| #include "linux/bpf.h" | ||
| #include <bpf/bpf_helpers.h> | ||
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| #define NF_DROP 0 | ||
| #define NF_ACCEPT 1 | ||
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| int bpf_dynptr_from_skb(struct sk_buff *skb, | ||
| __u64 flags, struct bpf_dynptr *ptr__uninit) __ksym; | ||
| void *bpf_dynptr_slice(const struct bpf_dynptr *ptr, | ||
| uint32_t offset, void *buffer, uint32_t buffer__sz) __ksym; | ||
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| struct ipv4_lpm_key { | ||
| __u32 prefixlen; | ||
| __u32 data; | ||
| }; | ||
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| struct { | ||
| __uint(type, BPF_MAP_TYPE_LPM_TRIE); | ||
| __type(key, struct ipv4_lpm_key); | ||
| __type(value, __u32); | ||
| __uint(map_flags, BPF_F_NO_PREALLOC); | ||
| __uint(max_entries, 200); | ||
| } ipv4_lpm_map SEC(".maps"); | ||
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| SEC("netfilter") | ||
| int netfilter_ip4block(struct bpf_nf_ctx *ctx) | ||
| { | ||
| struct sk_buff *skb = ctx->skb; | ||
| struct bpf_dynptr ptr; | ||
| struct iphdr *p, iph = {}; | ||
| struct ipv4_lpm_key key; | ||
| __u32 *pvalue; | ||
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| if (skb->len <= 20 || bpf_dynptr_from_skb(skb, 0, &ptr)) | ||
| return NF_ACCEPT; | ||
| p = bpf_dynptr_slice(&ptr, 0, &iph, sizeof(iph)); | ||
| if (!p) | ||
| return NF_ACCEPT; | ||
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| /* ip4 only */ | ||
| if (p->version != 4) | ||
| return NF_ACCEPT; | ||
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| /* search p->daddr in trie */ | ||
| key.prefixlen = 32; | ||
| key.data = p->daddr; | ||
| pvalue = bpf_map_lookup_elem(&ipv4_lpm_map, &key); | ||
| if (pvalue) { | ||
| /* cat /sys/kernel/debug/tracing/trace_pipe */ | ||
| bpf_printk("rule matched with %d...\n", *pvalue); | ||
| return NF_DROP; | ||
| } | ||
| return NF_ACCEPT; | ||
| } | ||
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| char _license[] SEC("license") = "GPL"; | ||
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