From: Daniel Borkmann <daniel@iogearbox.net>
To: Jesper Dangaard Brouer <brouer@redhat.com>, bpf@vger.kernel.org
Cc: 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: Re: [PATCH bpf-next V12 2/7] bpf: fix bpf_fib_lookup helper MTU check for SKB ctx
Date: Sat, 23 Jan 2021 02:47:28 +0100 [thread overview]
Message-ID: <06f94963-f16b-3339-abf2-6529b474a2f6@iogearbox.net> (raw)
In-Reply-To: <161098885996.108067.14467274374916086727.stgit@firesoul>
On 1/18/21 5:54 PM, Jesper Dangaard Brouer wrote:
> 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.
>
> 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 5beadd659091..d5e6f395cf64 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 net_device MTU
> + */
> dev = dev_get_by_index_rcu(net, params->ifindex);
> if (!is_skb_forwardable(dev, skb))
> rc = BPF_FIB_LKUP_RET_FRAG_NEEDED;
Btw, looking at some of the old feedback, looks like [0] got missed somehow. Would
be nice if we could simplify this rather ugly bit with refetching dev for tc.
[0] https://lore.kernel.org/bpf/f959017b-5d3c-5cdb-a016-c467a3c9a2fc@iogearbox.net/
https://lore.kernel.org/bpf/f8ff26f0-b1b6-6dd1-738d-4c592a8efdb0@gmail.com/
next prev parent reply other threads:[~2021-01-23 1:48 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-18 16:54 [PATCH bpf-next V12 0/7] bpf: New approach for BPF MTU handling Jesper Dangaard Brouer
2021-01-18 16:54 ` [PATCH bpf-next V12 1/7] bpf: Remove MTU check in __bpf_skb_max_len Jesper Dangaard Brouer
2021-01-18 16:54 ` [PATCH bpf-next V12 2/7] bpf: fix bpf_fib_lookup helper MTU check for SKB ctx Jesper Dangaard Brouer
2021-01-23 1:47 ` Daniel Borkmann [this message]
2021-01-25 15:58 ` Jesper Dangaard Brouer
2021-01-18 16:54 ` [PATCH bpf-next V12 3/7] bpf: bpf_fib_lookup return MTU value as output when looked up Jesper Dangaard Brouer
2021-01-18 16:54 ` [PATCH bpf-next V12 4/7] bpf: add BPF-helper for MTU checking Jesper Dangaard Brouer
2021-01-23 1:35 ` Daniel Borkmann
2021-01-25 8:41 ` Jesper Dangaard Brouer
2021-01-25 22:27 ` Daniel Borkmann
2021-01-26 9:13 ` Jesper Dangaard Brouer
2021-01-18 16:54 ` [PATCH bpf-next V12 5/7] bpf: drop MTU check when doing TC-BPF redirect to ingress Jesper Dangaard Brouer
2021-01-18 16:54 ` [PATCH bpf-next V12 6/7] selftests/bpf: use bpf_check_mtu in selftest test_cls_redirect Jesper Dangaard Brouer
2021-01-18 16:54 ` [PATCH bpf-next V12 7/7] bpf/selftests: tests using bpf_check_mtu BPF-helper Jesper Dangaard Brouer
2021-01-23 1:49 ` Daniel Borkmann
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