From: Jesper Dangaard Brouer <brouer@redhat.com> To: bpf@vger.kernel.org Cc: Jesper Dangaard Brouer <brouer@redhat.com>, netdev@vger.kernel.org, Daniel Borkmann <borkmann@iogearbox.net>, Alexei Starovoitov <alexei.starovoitov@gmail.com>, maze@google.com, lmb@cloudflare.com, shaun@tigera.io, Lorenzo Bianconi <lorenzo@kernel.org>, marek@cloudflare.com, John Fastabend <john.fastabend@gmail.com>, Jakub Kicinski <kuba@kernel.org>, eyal.birger@gmail.com, colrack@gmail.com Subject: [PATCH bpf-next V16 2/7] bpf: fix bpf_fib_lookup helper MTU check for SKB ctx Date: Tue, 09 Feb 2021 14:38:14 +0100 [thread overview] Message-ID: <161287789444.790810.15247494756551413508.stgit@firesoul> (raw) In-Reply-To: <161287779408.790810.15631860742170694244.stgit@firesoul> 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: 4c79579b44b1 ("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> --- net/core/filter.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/net/core/filter.c b/net/core/filter.c index 731571762f8d..46b06a693e39 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -5569,6 +5569,7 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb, { struct net *net = dev_net(skb->dev); int rc = -EAFNOSUPPORT; + bool check_mtu = false; if (plen < sizeof(*params)) return -EINVAL; @@ -5576,22 +5577,28 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb, if (flags & ~(BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT)) return -EINVAL; + if (params->tot_len) + check_mtu = true; + switch (params->family) { #if IS_ENABLED(CONFIG_INET) case AF_INET: - rc = bpf_ipv4_fib_lookup(net, params, flags, false); + rc = bpf_ipv4_fib_lookup(net, params, flags, check_mtu); break; #endif #if IS_ENABLED(CONFIG_IPV6) case AF_INET6: - rc = bpf_ipv6_fib_lookup(net, params, flags, false); + rc = bpf_ipv6_fib_lookup(net, params, flags, check_mtu); break; #endif } - if (!rc) { + if (rc == BPF_FIB_LKUP_RET_SUCCESS && !check_mtu) { struct net_device *dev; + /* When tot_len isn't provided by user, check skb + * against MTU of FIB lookup resulting net_device + */ dev = dev_get_by_index_rcu(net, params->ifindex); if (!is_skb_forwardable(dev, skb)) rc = BPF_FIB_LKUP_RET_FRAG_NEEDED;
next prev parent reply other threads:[~2021-02-09 13:40 UTC|newest] Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-02-09 13:38 [PATCH bpf-next V16 0/7] bpf: New approach for BPF MTU handling Jesper Dangaard Brouer 2021-02-09 13:38 ` [PATCH bpf-next V16 1/7] bpf: Remove MTU check in __bpf_skb_max_len Jesper Dangaard Brouer 2021-02-09 13:38 ` Jesper Dangaard Brouer [this message] 2021-02-09 13:38 ` [PATCH bpf-next V16 3/7] bpf: bpf_fib_lookup return MTU value as output when looked up Jesper Dangaard Brouer 2021-02-09 13:38 ` [PATCH bpf-next V16 4/7] bpf: add BPF-helper for MTU checking Jesper Dangaard Brouer 2021-02-09 13:38 ` [PATCH bpf-next V16 5/7] bpf: drop MTU check when doing TC-BPF redirect to ingress Jesper Dangaard Brouer 2021-02-09 13:38 ` [PATCH bpf-next V16 6/7] selftests/bpf: use bpf_check_mtu in selftest test_cls_redirect Jesper Dangaard Brouer 2021-02-09 13:38 ` [PATCH bpf-next V16 7/7] selftests/bpf: tests using bpf_check_mtu BPF-helper Jesper Dangaard Brouer 2021-02-13 0:20 ` [PATCH bpf-next V16 0/7] bpf: New approach for BPF MTU handling patchwork-bot+netdevbpf
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