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bpf: Fix bpf_fib_lookup helper MTU check for SKB ctx
[ Upstream commit2c0a10af68
] BPF end-user on Cilium slack-channel (Carlo Carraro) wants to use bpf_fib_lookup for doing MTU-check, but *prior* to extending packet size, by adjusting fib_params 'tot_len' with the packet length plus the expected encap size. (Just like the bpf_check_mtu helper supports). He discovered that for SKB ctx the param->tot_len was not used, instead skb->len was used (via MTU check in is_skb_forwardable() that checks against netdev MTU). Fix this by using fib_params 'tot_len' for MTU check. If not provided (e.g. zero) then keep existing TC behaviour intact. Notice that 'tot_len' for MTU check is done like XDP code-path, which checks against FIB-dst MTU. V16: - Revert V13 optimization, 2nd lookup is against egress/resulting netdev V13: - Only do ifindex lookup one time, calling dev_get_by_index_rcu(). V10: - Use same method as XDP for 'tot_len' MTU check Fixes:4c79579b44
("bpf: Change bpf_fib_lookup to return lookup status") Reported-by: Carlo Carraro <colrack@gmail.com> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/161287789444.790810.15247494756551413508.stgit@firesoul Signed-off-by: Sasha Levin <sashal@kernel.org>
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parent
5af224ab94
commit
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1 changed files with 10 additions and 3 deletions
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@ -4880,6 +4880,7 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb,
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{
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struct net *net = dev_net(skb->dev);
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int rc = -EAFNOSUPPORT;
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bool check_mtu = false;
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if (plen < sizeof(*params))
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return -EINVAL;
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@ -4887,22 +4888,28 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb,
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if (flags & ~(BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT))
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return -EINVAL;
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if (params->tot_len)
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check_mtu = true;
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switch (params->family) {
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#if IS_ENABLED(CONFIG_INET)
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case AF_INET:
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rc = bpf_ipv4_fib_lookup(net, params, flags, false);
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rc = bpf_ipv4_fib_lookup(net, params, flags, check_mtu);
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break;
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#endif
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#if IS_ENABLED(CONFIG_IPV6)
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case AF_INET6:
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rc = bpf_ipv6_fib_lookup(net, params, flags, false);
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rc = bpf_ipv6_fib_lookup(net, params, flags, check_mtu);
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break;
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#endif
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}
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if (!rc) {
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if (rc == BPF_FIB_LKUP_RET_SUCCESS && !check_mtu) {
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struct net_device *dev;
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/* When tot_len isn't provided by user, check skb
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* against MTU of FIB lookup resulting net_device
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*/
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dev = dev_get_by_index_rcu(net, params->ifindex);
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if (!is_skb_forwardable(dev, skb))
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rc = BPF_FIB_LKUP_RET_FRAG_NEEDED;
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