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b02d196c44
xmit_check_hhlen() observes the dst for getting the device hard header
length to make sure a modified packet can fit. When a helper which changes
the dst - such as bpf_skb_set_tunnel_key() - is called as part of the
xmit program the accessed dst is no longer valid.
This leads to the following splat:
BUG: kernel NULL pointer dereference, address: 00000000000000de
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP PTI
CPU: 0 PID: 798 Comm: ping Not tainted 5.18.0-rc2+ #103
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
RIP: 0010:bpf_xmit+0xfb/0x17f
Code: c6 c0 4d cd 8e 48 c7 c7 7d 33 f0 8e e8 42 09 fb ff 48 8b 45 58 48 8b 95 c8 00 00 00 48 2b 95 c0 00 00 00 48 83 e0 fe 48 8b 00 <0f> b7 80 de 00 00 00 39 c2 73 22 29 d0 b9 20 0a 00 00 31 d2 48 89
RSP: 0018:ffffb148c0bc7b98 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000240008 RCX: 0000000000000000
RDX: 0000000000000010 RSI: 00000000ffffffea RDI: 00000000ffffffff
RBP: ffff922a828a4e00 R08: ffffffff8f1350e8 R09: 00000000ffffdfff
R10: ffffffff8f055100 R11: ffffffff8f105100 R12: 0000000000000000
R13: ffff922a828a4e00 R14: 0000000000000040 R15: 0000000000000000
FS: 00007f414e8f0080(0000) GS:ffff922afdc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000000000de CR3: 0000000002d80006 CR4: 0000000000370ef0
Call Trace:
<TASK>
lwtunnel_xmit.cold+0x71/0xc8
ip_finish_output2+0x279/0x520
? __ip_finish_output.part.0+0x21/0x130
Fix by fetching the device hard header length before running the BPF code.
Fixes: 3a0af8fd61
("bpf: BPF for lightweight tunnel infrastructure")
Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220420165219.1755407-1-eyal.birger@gmail.com
659 lines
15 KiB
C
659 lines
15 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* Copyright (c) 2016 Thomas Graf <tgraf@tgraf.ch>
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*/
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#include <linux/filter.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/types.h>
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#include <linux/bpf.h>
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#include <net/lwtunnel.h>
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#include <net/gre.h>
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#include <net/ip6_route.h>
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#include <net/ipv6_stubs.h>
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struct bpf_lwt_prog {
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struct bpf_prog *prog;
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char *name;
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};
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struct bpf_lwt {
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struct bpf_lwt_prog in;
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struct bpf_lwt_prog out;
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struct bpf_lwt_prog xmit;
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int family;
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};
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#define MAX_PROG_NAME 256
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static inline struct bpf_lwt *bpf_lwt_lwtunnel(struct lwtunnel_state *lwt)
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{
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return (struct bpf_lwt *)lwt->data;
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}
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#define NO_REDIRECT false
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#define CAN_REDIRECT true
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static int run_lwt_bpf(struct sk_buff *skb, struct bpf_lwt_prog *lwt,
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struct dst_entry *dst, bool can_redirect)
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{
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int ret;
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/* Migration disable and BH disable are needed to protect per-cpu
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* redirect_info between BPF prog and skb_do_redirect().
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*/
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migrate_disable();
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local_bh_disable();
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bpf_compute_data_pointers(skb);
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ret = bpf_prog_run_save_cb(lwt->prog, skb);
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switch (ret) {
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case BPF_OK:
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case BPF_LWT_REROUTE:
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break;
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case BPF_REDIRECT:
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if (unlikely(!can_redirect)) {
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pr_warn_once("Illegal redirect return code in prog %s\n",
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lwt->name ? : "<unknown>");
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ret = BPF_OK;
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} else {
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skb_reset_mac_header(skb);
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ret = skb_do_redirect(skb);
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if (ret == 0)
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ret = BPF_REDIRECT;
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}
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break;
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case BPF_DROP:
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kfree_skb(skb);
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ret = -EPERM;
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break;
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default:
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pr_warn_once("bpf-lwt: Illegal return value %u, expect packet loss\n", ret);
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kfree_skb(skb);
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ret = -EINVAL;
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break;
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}
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local_bh_enable();
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migrate_enable();
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return ret;
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}
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static int bpf_lwt_input_reroute(struct sk_buff *skb)
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{
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int err = -EINVAL;
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if (skb->protocol == htons(ETH_P_IP)) {
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struct net_device *dev = skb_dst(skb)->dev;
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struct iphdr *iph = ip_hdr(skb);
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dev_hold(dev);
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skb_dst_drop(skb);
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err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
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iph->tos, dev);
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dev_put(dev);
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} else if (skb->protocol == htons(ETH_P_IPV6)) {
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skb_dst_drop(skb);
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err = ipv6_stub->ipv6_route_input(skb);
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} else {
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err = -EAFNOSUPPORT;
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}
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if (err)
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goto err;
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return dst_input(skb);
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err:
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kfree_skb(skb);
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return err;
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}
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static int bpf_input(struct sk_buff *skb)
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{
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struct dst_entry *dst = skb_dst(skb);
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struct bpf_lwt *bpf;
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int ret;
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bpf = bpf_lwt_lwtunnel(dst->lwtstate);
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if (bpf->in.prog) {
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ret = run_lwt_bpf(skb, &bpf->in, dst, NO_REDIRECT);
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if (ret < 0)
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return ret;
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if (ret == BPF_LWT_REROUTE)
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return bpf_lwt_input_reroute(skb);
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}
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if (unlikely(!dst->lwtstate->orig_input)) {
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kfree_skb(skb);
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return -EINVAL;
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}
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return dst->lwtstate->orig_input(skb);
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}
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static int bpf_output(struct net *net, struct sock *sk, struct sk_buff *skb)
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{
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struct dst_entry *dst = skb_dst(skb);
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struct bpf_lwt *bpf;
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int ret;
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bpf = bpf_lwt_lwtunnel(dst->lwtstate);
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if (bpf->out.prog) {
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ret = run_lwt_bpf(skb, &bpf->out, dst, NO_REDIRECT);
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if (ret < 0)
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return ret;
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}
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if (unlikely(!dst->lwtstate->orig_output)) {
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pr_warn_once("orig_output not set on dst for prog %s\n",
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bpf->out.name);
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kfree_skb(skb);
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return -EINVAL;
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}
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return dst->lwtstate->orig_output(net, sk, skb);
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}
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static int xmit_check_hhlen(struct sk_buff *skb, int hh_len)
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{
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if (skb_headroom(skb) < hh_len) {
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int nhead = HH_DATA_ALIGN(hh_len - skb_headroom(skb));
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if (pskb_expand_head(skb, nhead, 0, GFP_ATOMIC))
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return -ENOMEM;
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}
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return 0;
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}
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static int bpf_lwt_xmit_reroute(struct sk_buff *skb)
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{
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struct net_device *l3mdev = l3mdev_master_dev_rcu(skb_dst(skb)->dev);
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int oif = l3mdev ? l3mdev->ifindex : 0;
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struct dst_entry *dst = NULL;
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int err = -EAFNOSUPPORT;
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struct sock *sk;
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struct net *net;
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bool ipv4;
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if (skb->protocol == htons(ETH_P_IP))
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ipv4 = true;
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else if (skb->protocol == htons(ETH_P_IPV6))
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ipv4 = false;
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else
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goto err;
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sk = sk_to_full_sk(skb->sk);
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if (sk) {
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if (sk->sk_bound_dev_if)
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oif = sk->sk_bound_dev_if;
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net = sock_net(sk);
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} else {
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net = dev_net(skb_dst(skb)->dev);
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}
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if (ipv4) {
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struct iphdr *iph = ip_hdr(skb);
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struct flowi4 fl4 = {};
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struct rtable *rt;
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fl4.flowi4_oif = oif;
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fl4.flowi4_mark = skb->mark;
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fl4.flowi4_uid = sock_net_uid(net, sk);
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fl4.flowi4_tos = RT_TOS(iph->tos);
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fl4.flowi4_flags = FLOWI_FLAG_ANYSRC;
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fl4.flowi4_proto = iph->protocol;
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fl4.daddr = iph->daddr;
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fl4.saddr = iph->saddr;
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rt = ip_route_output_key(net, &fl4);
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if (IS_ERR(rt)) {
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err = PTR_ERR(rt);
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goto err;
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}
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dst = &rt->dst;
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} else {
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struct ipv6hdr *iph6 = ipv6_hdr(skb);
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struct flowi6 fl6 = {};
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fl6.flowi6_oif = oif;
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fl6.flowi6_mark = skb->mark;
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fl6.flowi6_uid = sock_net_uid(net, sk);
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fl6.flowlabel = ip6_flowinfo(iph6);
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fl6.flowi6_proto = iph6->nexthdr;
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fl6.daddr = iph6->daddr;
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fl6.saddr = iph6->saddr;
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dst = ipv6_stub->ipv6_dst_lookup_flow(net, skb->sk, &fl6, NULL);
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if (IS_ERR(dst)) {
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err = PTR_ERR(dst);
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goto err;
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}
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}
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if (unlikely(dst->error)) {
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err = dst->error;
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dst_release(dst);
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goto err;
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}
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/* Although skb header was reserved in bpf_lwt_push_ip_encap(), it
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* was done for the previous dst, so we are doing it here again, in
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* case the new dst needs much more space. The call below is a noop
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* if there is enough header space in skb.
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*/
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err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
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if (unlikely(err))
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goto err;
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skb_dst_drop(skb);
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skb_dst_set(skb, dst);
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err = dst_output(dev_net(skb_dst(skb)->dev), skb->sk, skb);
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if (unlikely(err))
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return err;
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/* ip[6]_finish_output2 understand LWTUNNEL_XMIT_DONE */
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return LWTUNNEL_XMIT_DONE;
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err:
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kfree_skb(skb);
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return err;
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}
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static int bpf_xmit(struct sk_buff *skb)
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{
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struct dst_entry *dst = skb_dst(skb);
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struct bpf_lwt *bpf;
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bpf = bpf_lwt_lwtunnel(dst->lwtstate);
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if (bpf->xmit.prog) {
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int hh_len = dst->dev->hard_header_len;
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__be16 proto = skb->protocol;
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int ret;
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ret = run_lwt_bpf(skb, &bpf->xmit, dst, CAN_REDIRECT);
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switch (ret) {
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case BPF_OK:
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/* If the header changed, e.g. via bpf_lwt_push_encap,
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* BPF_LWT_REROUTE below should have been used if the
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* protocol was also changed.
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*/
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if (skb->protocol != proto) {
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kfree_skb(skb);
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return -EINVAL;
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}
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/* If the header was expanded, headroom might be too
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* small for L2 header to come, expand as needed.
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*/
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ret = xmit_check_hhlen(skb, hh_len);
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if (unlikely(ret))
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return ret;
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return LWTUNNEL_XMIT_CONTINUE;
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case BPF_REDIRECT:
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return LWTUNNEL_XMIT_DONE;
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case BPF_LWT_REROUTE:
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return bpf_lwt_xmit_reroute(skb);
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default:
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return ret;
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}
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}
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return LWTUNNEL_XMIT_CONTINUE;
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}
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static void bpf_lwt_prog_destroy(struct bpf_lwt_prog *prog)
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{
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if (prog->prog)
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bpf_prog_put(prog->prog);
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kfree(prog->name);
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}
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static void bpf_destroy_state(struct lwtunnel_state *lwt)
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{
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struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);
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bpf_lwt_prog_destroy(&bpf->in);
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bpf_lwt_prog_destroy(&bpf->out);
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bpf_lwt_prog_destroy(&bpf->xmit);
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}
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static const struct nla_policy bpf_prog_policy[LWT_BPF_PROG_MAX + 1] = {
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[LWT_BPF_PROG_FD] = { .type = NLA_U32, },
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[LWT_BPF_PROG_NAME] = { .type = NLA_NUL_STRING,
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.len = MAX_PROG_NAME },
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};
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static int bpf_parse_prog(struct nlattr *attr, struct bpf_lwt_prog *prog,
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enum bpf_prog_type type)
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{
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struct nlattr *tb[LWT_BPF_PROG_MAX + 1];
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struct bpf_prog *p;
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int ret;
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u32 fd;
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ret = nla_parse_nested_deprecated(tb, LWT_BPF_PROG_MAX, attr,
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bpf_prog_policy, NULL);
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if (ret < 0)
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return ret;
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if (!tb[LWT_BPF_PROG_FD] || !tb[LWT_BPF_PROG_NAME])
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return -EINVAL;
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prog->name = nla_memdup(tb[LWT_BPF_PROG_NAME], GFP_ATOMIC);
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if (!prog->name)
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return -ENOMEM;
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fd = nla_get_u32(tb[LWT_BPF_PROG_FD]);
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p = bpf_prog_get_type(fd, type);
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if (IS_ERR(p))
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return PTR_ERR(p);
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prog->prog = p;
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return 0;
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}
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static const struct nla_policy bpf_nl_policy[LWT_BPF_MAX + 1] = {
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[LWT_BPF_IN] = { .type = NLA_NESTED, },
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[LWT_BPF_OUT] = { .type = NLA_NESTED, },
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[LWT_BPF_XMIT] = { .type = NLA_NESTED, },
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[LWT_BPF_XMIT_HEADROOM] = { .type = NLA_U32 },
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};
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static int bpf_build_state(struct net *net, struct nlattr *nla,
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unsigned int family, const void *cfg,
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struct lwtunnel_state **ts,
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struct netlink_ext_ack *extack)
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{
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struct nlattr *tb[LWT_BPF_MAX + 1];
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struct lwtunnel_state *newts;
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struct bpf_lwt *bpf;
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int ret;
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if (family != AF_INET && family != AF_INET6)
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return -EAFNOSUPPORT;
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ret = nla_parse_nested_deprecated(tb, LWT_BPF_MAX, nla, bpf_nl_policy,
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extack);
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if (ret < 0)
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return ret;
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if (!tb[LWT_BPF_IN] && !tb[LWT_BPF_OUT] && !tb[LWT_BPF_XMIT])
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return -EINVAL;
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newts = lwtunnel_state_alloc(sizeof(*bpf));
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if (!newts)
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return -ENOMEM;
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newts->type = LWTUNNEL_ENCAP_BPF;
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bpf = bpf_lwt_lwtunnel(newts);
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if (tb[LWT_BPF_IN]) {
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newts->flags |= LWTUNNEL_STATE_INPUT_REDIRECT;
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ret = bpf_parse_prog(tb[LWT_BPF_IN], &bpf->in,
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BPF_PROG_TYPE_LWT_IN);
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if (ret < 0)
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goto errout;
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}
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if (tb[LWT_BPF_OUT]) {
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newts->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT;
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ret = bpf_parse_prog(tb[LWT_BPF_OUT], &bpf->out,
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BPF_PROG_TYPE_LWT_OUT);
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if (ret < 0)
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goto errout;
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}
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if (tb[LWT_BPF_XMIT]) {
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newts->flags |= LWTUNNEL_STATE_XMIT_REDIRECT;
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ret = bpf_parse_prog(tb[LWT_BPF_XMIT], &bpf->xmit,
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BPF_PROG_TYPE_LWT_XMIT);
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if (ret < 0)
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goto errout;
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}
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if (tb[LWT_BPF_XMIT_HEADROOM]) {
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u32 headroom = nla_get_u32(tb[LWT_BPF_XMIT_HEADROOM]);
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if (headroom > LWT_BPF_MAX_HEADROOM) {
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ret = -ERANGE;
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goto errout;
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}
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newts->headroom = headroom;
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}
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bpf->family = family;
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*ts = newts;
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return 0;
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errout:
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bpf_destroy_state(newts);
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kfree(newts);
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return ret;
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}
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static int bpf_fill_lwt_prog(struct sk_buff *skb, int attr,
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struct bpf_lwt_prog *prog)
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{
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struct nlattr *nest;
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if (!prog->prog)
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return 0;
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nest = nla_nest_start_noflag(skb, attr);
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if (!nest)
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return -EMSGSIZE;
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if (prog->name &&
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nla_put_string(skb, LWT_BPF_PROG_NAME, prog->name))
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return -EMSGSIZE;
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return nla_nest_end(skb, nest);
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}
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static int bpf_fill_encap_info(struct sk_buff *skb, struct lwtunnel_state *lwt)
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{
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struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);
|
|
|
|
if (bpf_fill_lwt_prog(skb, LWT_BPF_IN, &bpf->in) < 0 ||
|
|
bpf_fill_lwt_prog(skb, LWT_BPF_OUT, &bpf->out) < 0 ||
|
|
bpf_fill_lwt_prog(skb, LWT_BPF_XMIT, &bpf->xmit) < 0)
|
|
return -EMSGSIZE;
|
|
|
|
return 0;
|
|
}
|
|
|
|
static int bpf_encap_nlsize(struct lwtunnel_state *lwtstate)
|
|
{
|
|
int nest_len = nla_total_size(sizeof(struct nlattr)) +
|
|
nla_total_size(MAX_PROG_NAME) + /* LWT_BPF_PROG_NAME */
|
|
0;
|
|
|
|
return nest_len + /* LWT_BPF_IN */
|
|
nest_len + /* LWT_BPF_OUT */
|
|
nest_len + /* LWT_BPF_XMIT */
|
|
0;
|
|
}
|
|
|
|
static int bpf_lwt_prog_cmp(struct bpf_lwt_prog *a, struct bpf_lwt_prog *b)
|
|
{
|
|
/* FIXME:
|
|
* The LWT state is currently rebuilt for delete requests which
|
|
* results in a new bpf_prog instance. Comparing names for now.
|
|
*/
|
|
if (!a->name && !b->name)
|
|
return 0;
|
|
|
|
if (!a->name || !b->name)
|
|
return 1;
|
|
|
|
return strcmp(a->name, b->name);
|
|
}
|
|
|
|
static int bpf_encap_cmp(struct lwtunnel_state *a, struct lwtunnel_state *b)
|
|
{
|
|
struct bpf_lwt *a_bpf = bpf_lwt_lwtunnel(a);
|
|
struct bpf_lwt *b_bpf = bpf_lwt_lwtunnel(b);
|
|
|
|
return bpf_lwt_prog_cmp(&a_bpf->in, &b_bpf->in) ||
|
|
bpf_lwt_prog_cmp(&a_bpf->out, &b_bpf->out) ||
|
|
bpf_lwt_prog_cmp(&a_bpf->xmit, &b_bpf->xmit);
|
|
}
|
|
|
|
static const struct lwtunnel_encap_ops bpf_encap_ops = {
|
|
.build_state = bpf_build_state,
|
|
.destroy_state = bpf_destroy_state,
|
|
.input = bpf_input,
|
|
.output = bpf_output,
|
|
.xmit = bpf_xmit,
|
|
.fill_encap = bpf_fill_encap_info,
|
|
.get_encap_size = bpf_encap_nlsize,
|
|
.cmp_encap = bpf_encap_cmp,
|
|
.owner = THIS_MODULE,
|
|
};
|
|
|
|
static int handle_gso_type(struct sk_buff *skb, unsigned int gso_type,
|
|
int encap_len)
|
|
{
|
|
struct skb_shared_info *shinfo = skb_shinfo(skb);
|
|
|
|
gso_type |= SKB_GSO_DODGY;
|
|
shinfo->gso_type |= gso_type;
|
|
skb_decrease_gso_size(shinfo, encap_len);
|
|
shinfo->gso_segs = 0;
|
|
return 0;
|
|
}
|
|
|
|
static int handle_gso_encap(struct sk_buff *skb, bool ipv4, int encap_len)
|
|
{
|
|
int next_hdr_offset;
|
|
void *next_hdr;
|
|
__u8 protocol;
|
|
|
|
/* SCTP and UDP_L4 gso need more nuanced handling than what
|
|
* handle_gso_type() does above: skb_decrease_gso_size() is not enough.
|
|
* So at the moment only TCP GSO packets are let through.
|
|
*/
|
|
if (!(skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
|
|
return -ENOTSUPP;
|
|
|
|
if (ipv4) {
|
|
protocol = ip_hdr(skb)->protocol;
|
|
next_hdr_offset = sizeof(struct iphdr);
|
|
next_hdr = skb_network_header(skb) + next_hdr_offset;
|
|
} else {
|
|
protocol = ipv6_hdr(skb)->nexthdr;
|
|
next_hdr_offset = sizeof(struct ipv6hdr);
|
|
next_hdr = skb_network_header(skb) + next_hdr_offset;
|
|
}
|
|
|
|
switch (protocol) {
|
|
case IPPROTO_GRE:
|
|
next_hdr_offset += sizeof(struct gre_base_hdr);
|
|
if (next_hdr_offset > encap_len)
|
|
return -EINVAL;
|
|
|
|
if (((struct gre_base_hdr *)next_hdr)->flags & GRE_CSUM)
|
|
return handle_gso_type(skb, SKB_GSO_GRE_CSUM,
|
|
encap_len);
|
|
return handle_gso_type(skb, SKB_GSO_GRE, encap_len);
|
|
|
|
case IPPROTO_UDP:
|
|
next_hdr_offset += sizeof(struct udphdr);
|
|
if (next_hdr_offset > encap_len)
|
|
return -EINVAL;
|
|
|
|
if (((struct udphdr *)next_hdr)->check)
|
|
return handle_gso_type(skb, SKB_GSO_UDP_TUNNEL_CSUM,
|
|
encap_len);
|
|
return handle_gso_type(skb, SKB_GSO_UDP_TUNNEL, encap_len);
|
|
|
|
case IPPROTO_IP:
|
|
case IPPROTO_IPV6:
|
|
if (ipv4)
|
|
return handle_gso_type(skb, SKB_GSO_IPXIP4, encap_len);
|
|
else
|
|
return handle_gso_type(skb, SKB_GSO_IPXIP6, encap_len);
|
|
|
|
default:
|
|
return -EPROTONOSUPPORT;
|
|
}
|
|
}
|
|
|
|
int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len, bool ingress)
|
|
{
|
|
struct iphdr *iph;
|
|
bool ipv4;
|
|
int err;
|
|
|
|
if (unlikely(len < sizeof(struct iphdr) || len > LWT_BPF_MAX_HEADROOM))
|
|
return -EINVAL;
|
|
|
|
/* validate protocol and length */
|
|
iph = (struct iphdr *)hdr;
|
|
if (iph->version == 4) {
|
|
ipv4 = true;
|
|
if (unlikely(len < iph->ihl * 4))
|
|
return -EINVAL;
|
|
} else if (iph->version == 6) {
|
|
ipv4 = false;
|
|
if (unlikely(len < sizeof(struct ipv6hdr)))
|
|
return -EINVAL;
|
|
} else {
|
|
return -EINVAL;
|
|
}
|
|
|
|
if (ingress)
|
|
err = skb_cow_head(skb, len + skb->mac_len);
|
|
else
|
|
err = skb_cow_head(skb,
|
|
len + LL_RESERVED_SPACE(skb_dst(skb)->dev));
|
|
if (unlikely(err))
|
|
return err;
|
|
|
|
/* push the encap headers and fix pointers */
|
|
skb_reset_inner_headers(skb);
|
|
skb_reset_inner_mac_header(skb); /* mac header is not yet set */
|
|
skb_set_inner_protocol(skb, skb->protocol);
|
|
skb->encapsulation = 1;
|
|
skb_push(skb, len);
|
|
if (ingress)
|
|
skb_postpush_rcsum(skb, iph, len);
|
|
skb_reset_network_header(skb);
|
|
memcpy(skb_network_header(skb), hdr, len);
|
|
bpf_compute_data_pointers(skb);
|
|
skb_clear_hash(skb);
|
|
|
|
if (ipv4) {
|
|
skb->protocol = htons(ETH_P_IP);
|
|
iph = ip_hdr(skb);
|
|
|
|
if (!iph->check)
|
|
iph->check = ip_fast_csum((unsigned char *)iph,
|
|
iph->ihl);
|
|
} else {
|
|
skb->protocol = htons(ETH_P_IPV6);
|
|
}
|
|
|
|
if (skb_is_gso(skb))
|
|
return handle_gso_encap(skb, ipv4, len);
|
|
|
|
return 0;
|
|
}
|
|
|
|
static int __init bpf_lwt_init(void)
|
|
{
|
|
return lwtunnel_encap_add_ops(&bpf_encap_ops, LWTUNNEL_ENCAP_BPF);
|
|
}
|
|
|
|
subsys_initcall(bpf_lwt_init)
|