Re: [PATCH bpf-next 6/6] bpf: add test_run support for netfilter program type

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On Wed, Apr 05, 2023 at 06:11:16PM +0200, Florian Westphal wrote:
> also add two simple retval tests: as-is, a return value other
> than accept or drop will cause issues.
> 
> NF_QUEUE could be implemented later IFF we can guarantee that
> attachment of such programs can be rejected if they get attached
> to a pf/hook that doesn't support async reinjection.
> 
> NF_STOLEN could be implemented via trusted helpers that will eventually
> free the skb, else this would leak the skb reference.
> 
> Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
> ---
>  include/linux/bpf.h                           |   3 +
>  net/bpf/test_run.c                            | 143 ++++++++++++++++++
>  net/netfilter/nf_bpf_link.c                   |   1 +
>  .../selftests/bpf/verifier/netfilter.c        |  23 +++
>  4 files changed, 170 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/verifier/netfilter.c
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 2d8f3f639e68..453cee1efdd3 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2235,6 +2235,9 @@ int bpf_prog_test_run_raw_tp(struct bpf_prog *prog,
>  int bpf_prog_test_run_sk_lookup(struct bpf_prog *prog,
>  				const union bpf_attr *kattr,
>  				union bpf_attr __user *uattr);
> +int bpf_prog_test_run_nf(struct bpf_prog *prog,
> +			 const union bpf_attr *kattr,
> +			 union bpf_attr __user *uattr);
>  bool btf_ctx_access(int off, int size, enum bpf_access_type type,
>  		    const struct bpf_prog *prog,
>  		    struct bpf_insn_access_aux *info);
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index f1652f5fbd2e..c14f577fd987 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -19,7 +19,9 @@
>  #include <linux/error-injection.h>
>  #include <linux/smp.h>
>  #include <linux/sock_diag.h>
> +#include <linux/netfilter.h>
>  #include <net/xdp.h>
> +#include <net/netfilter/nf_bpf_link.h>
>  
>  #define CREATE_TRACE_POINTS
>  #include <trace/events/bpf_test_run.h>
> @@ -1690,6 +1692,147 @@ int bpf_prog_test_run_syscall(struct bpf_prog *prog,
>  	return err;
>  }
>  
> +static int verify_and_copy_hook_state(struct nf_hook_state *state,
> +				      const struct nf_hook_state *user,
> +				      struct net_device *dev)
> +{
> +	if (user->in || user->out)
> +		return -EINVAL;
> +
> +	if (user->net || user->sk || user->okfn)
> +		return -EINVAL;
> +
> +	switch (user->pf) {
> +	case NFPROTO_IPV4:
> +	case NFPROTO_IPV6:
> +		switch (state->hook) {
> +		case NF_INET_PRE_ROUTING:
> +			state->in = dev;
> +			break;
> +		case NF_INET_LOCAL_IN:
> +			state->in = dev;
> +			break;
> +		case NF_INET_FORWARD:
> +			state->in = dev;
> +			state->out = dev;
> +			break;
> +		case NF_INET_LOCAL_OUT:
> +			state->out = dev;
> +			break;
> +		case NF_INET_POST_ROUTING:
> +			state->out = dev;
> +			break;
> +		}
> +
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	state->pf = user->pf;
> +	state->hook = user->hook;
> +
> +	return 0;
> +}
> +
> +int bpf_prog_test_run_nf(struct bpf_prog *prog,
> +			 const union bpf_attr *kattr,
> +			 union bpf_attr __user *uattr)
> +{
> +	struct net *net = current->nsproxy->net_ns;
> +	struct net_device *dev = net->loopback_dev;
> +	struct nf_hook_state *user_ctx, hook_state = {
> +		.pf = NFPROTO_IPV4,
> +		.hook = NF_INET_PRE_ROUTING,
> +	};
> +	u32 size = kattr->test.data_size_in;
> +	u32 repeat = kattr->test.repeat;
> +	const struct ethhdr *eth;
> +	struct bpf_nf_ctx ctx = {
> +		.state = &hook_state,
> +	};
> +	struct sk_buff *skb = NULL;
> +	u32 retval, duration;
> +	void *data;
> +	int ret;
> +
> +	if (kattr->test.flags || kattr->test.cpu || kattr->test.batch_size)
> +		return -EINVAL;
> +
> +	if (size < ETH_HLEN + sizeof(struct iphdr))
> +		return -EINVAL;
> +
> +	data = bpf_test_init(kattr, kattr->test.data_size_in, size,
> +			     NET_SKB_PAD + NET_IP_ALIGN,
> +			     SKB_DATA_ALIGN(sizeof(struct skb_shared_info)));
> +	if (IS_ERR(data))
> +		return PTR_ERR(data);
> +
> +	eth = (struct ethhdr *)data;
> +
> +	if (!repeat)
> +		repeat = 1;
> +
> +	user_ctx = bpf_ctx_init(kattr, sizeof(struct nf_hook_state));
> +	if (IS_ERR(user_ctx)) {
> +		kfree(data);
> +		return PTR_ERR(user_ctx);
> +	}
> +
> +	if (user_ctx) {
> +		ret = verify_and_copy_hook_state(&hook_state, user_ctx, dev);
> +		if (ret)
> +			goto out;
> +	}
> +
> +	skb = slab_build_skb(data);
> +	if (!skb) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	data = NULL; /* data released via kfree_skb */
> +
> +	skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN);
> +	__skb_put(skb, size);
> +
> +	skb->protocol = eth_type_trans(skb, dev);
> +
> +	skb_reset_network_header(skb);
> +
> +	ret = -EINVAL;
> +
> +	switch (skb->protocol) {
> +	case htons(ETH_P_IP):
> +		if (hook_state.pf == NFPROTO_IPV4)
> +			break;
> +		goto out;
> +	case htons(ETH_P_IPV6):
> +		if (size < ETH_HLEN + sizeof(struct ipv6hdr))
> +			goto out;
> +		if (hook_state.pf == NFPROTO_IPV6)
> +			break;
> +		goto out;
> +	default:
> +		ret = -EPROTO;
> +		goto out;
> +	}
> +
> +	ctx.skb = skb;
> +
> +	ret = bpf_test_run(prog, &ctx, repeat, &retval, &duration, false);
> +	if (ret)
> +		goto out;
> +
> +	ret = bpf_test_finish(kattr, uattr, NULL, NULL, 0, retval, duration);
> +
> +out:
> +	kfree(user_ctx);
> +	kfree_skb(skb);
> +	kfree(data);
> +	return ret;
> +}
> +
>  static const struct btf_kfunc_id_set bpf_prog_test_kfunc_set = {
>  	.owner = THIS_MODULE,
>  	.set   = &test_sk_check_kfunc_ids,
> diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
> index 4b22a31d6df5..c27fd569adf1 100644
> --- a/net/netfilter/nf_bpf_link.c
> +++ b/net/netfilter/nf_bpf_link.c
> @@ -128,6 +128,7 @@ int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
>  }
>  
>  const struct bpf_prog_ops netfilter_prog_ops = {
> +	.test_run = bpf_prog_test_run_nf,
>  };
>  
>  static bool nf_ptr_to_btf_id(struct bpf_insn_access_aux *info, const char *name)
> diff --git a/tools/testing/selftests/bpf/verifier/netfilter.c b/tools/testing/selftests/bpf/verifier/netfilter.c
> new file mode 100644
> index 000000000000..deeb87afdf50
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/verifier/netfilter.c
> @@ -0,0 +1,23 @@
> +{
> +	"netfilter, accept all",
> +	.insns = {
> +	BPF_MOV64_IMM(BPF_REG_0, 1),
> +	BPF_EXIT_INSN(),
> +	},
> +	.result = ACCEPT,
> +	.prog_type = BPF_PROG_TYPE_NETFILTER,
> +	.retval = 1,
> +	.data = {
> +		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x08, 0x00,
> +	},
> +},
> +{
> +	"netfilter, stolen verdict",
> +	.insns = {
> +	BPF_MOV64_IMM(BPF_REG_0, 2),
> +	BPF_EXIT_INSN(),
> +	},
> +	.result = REJECT,
> +	.errstr = "At program exit the register R0 has value (0x2; 0x0) should have been in (0x0; 0x1)",
> +	.prog_type = BPF_PROG_TYPE_NETFILTER,

We're adding all new asm tests to test_progs now instead of test_verifier. See progs/verifier_*.c.

Other than this nit and build bot complains it looks good to me.



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