From: sdf@google.com
To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: bpf@vger.kernel.org, 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 V7 4/8] bpf: add BPF-helper for MTU checking
Date: Thu, 3 Dec 2020 10:25:41 -0800 [thread overview]
Message-ID: <X8ktpX/BYfiL0l2l@google.com> (raw)
In-Reply-To: <160588910708.2817268.17750536562819017509.stgit@firesoul>
On 11/20, Jesper Dangaard Brouer wrote:
> This BPF-helper bpf_check_mtu() works for both XDP and TC-BPF programs.
> The SKB object is complex and the skb->len value (accessible from
> BPF-prog) also include the length of any extra GRO/GSO segments, but
> without taking into account that these GRO/GSO segments get added
> transport (L4) and network (L3) headers before being transmitted. Thus,
> this BPF-helper is created such that the BPF-programmer don't need to
> handle these details in the BPF-prog.
> The API is designed to help the BPF-programmer, that want to do packet
> context size changes, which involves other helpers. These other helpers
> usually does a delta size adjustment. This helper also support a delta
> size (len_diff), which allow BPF-programmer to reuse arguments needed by
> these other helpers, and perform the MTU check prior to doing any actual
> size adjustment of the packet context.
> It is on purpose, that we allow the len adjustment to become a negative
> result, that will pass the MTU check. This might seem weird, but it's not
> this helpers responsibility to "catch" wrong len_diff adjustments. Other
> helpers will take care of these checks, if BPF-programmer chooses to do
> actual size adjustment.
> V6:
> - Took John's advice and dropped BPF_MTU_CHK_RELAX
> - Returned MTU is kept at L3-level (like fib_lookup)
> V4: Lot of changes
> - ifindex 0 now use current netdev for MTU lookup
> - rename helper from bpf_mtu_check to bpf_check_mtu
> - fix bug for GSO pkt length (as skb->len is total len)
> - remove __bpf_len_adj_positive, simply allow negative len adj
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> ---
> include/uapi/linux/bpf.h | 67 ++++++++++++++++++++++
> net/core/filter.c | 122
> ++++++++++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 67 ++++++++++++++++++++++
> 3 files changed, 256 insertions(+)
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index beacd312ea17..2619ea8c5a08 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3790,6 +3790,61 @@ union bpf_attr {
> * *ARG_PTR_TO_BTF_ID* of type *task_struct*.
> * Return
> * Pointer to the current task.
> + *
> + * int bpf_check_mtu(void *ctx, u32 ifindex, u32 *mtu_len, s32 len_diff,
> u64 flags)
> + * Description
> + * Check ctx packet size against MTU of net device (based on
> + * *ifindex*). This helper will likely be used in combination with
> + * helpers that adjust/change the packet size. The argument
> + * *len_diff* can be used for querying with a planned size
> + * change. This allows to check MTU prior to changing packet ctx.
> + *
> + * Specifying *ifindex* zero means the MTU check is performed
> + * against the current net device. This is practical if this isn't
> + * used prior to redirect.
> + *
> + * The Linux kernel route table can configure MTUs on a more
> + * specific per route level, which is not provided by this helper.
> + * For route level MTU checks use the **bpf_fib_lookup**\ ()
> + * helper.
> + *
> + * *ctx* is either **struct xdp_md** for XDP programs or
> + * **struct sk_buff** for tc cls_act programs.
> + *
> + * The *flags* argument can be a combination of one or more of the
> + * following values:
> + *
> + * **BPF_MTU_CHK_SEGS**
> + * This flag will only works for *ctx* **struct sk_buff**.
> + * If packet context contains extra packet segment buffers
> + * (often knows as GSO skb), then MTU check is harder to
> + * check at this point, because in transmit path it is
> + * possible for the skb packet to get re-segmented
> + * (depending on net device features). This could still be
> + * a MTU violation, so this flag enables performing MTU
> + * check against segments, with a different violation
> + * return code to tell it apart. Check cannot use len_diff.
> + *
> + * On return *mtu_len* pointer contains the MTU value of the net
> + * device. Remember the net device configured MTU is the L3 size,
> + * which is returned here and XDP and TX length operate at L2.
> + * Helper take this into account for you, but remember when using
> + * MTU value in your BPF-code. On input *mtu_len* must be a valid
> + * pointer and be initialized (to zero), else verifier will reject
> + * BPF program.
> + *
> + * Return
> + * * 0 on success, and populate MTU value in *mtu_len* pointer.
> + *
> + * * < 0 if any input argument is invalid (*mtu_len* not updated)
> + *
> + * MTU violations return positive values, but also populate MTU
> + * value in *mtu_len* pointer, as this can be needed for
> + * implementing PMTU handing:
> + *
> + * * **BPF_MTU_CHK_RET_FRAG_NEEDED**
> + * * **BPF_MTU_CHK_RET_SEGS_TOOBIG**
> + *
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -3951,6 +4006,7 @@ union bpf_attr {
> FN(task_storage_get), \
> FN(task_storage_delete), \
> FN(get_current_task_btf), \
> + FN(check_mtu), \
> /* */
> /* integer value in 'imm' field of BPF_CALL instruction selects which
> helper
> @@ -4978,6 +5034,17 @@ struct bpf_redir_neigh {
> };
> };
> +/* bpf_check_mtu flags*/
> +enum bpf_check_mtu_flags {
> + BPF_MTU_CHK_SEGS = (1U << 0),
> +};
> +
> +enum bpf_check_mtu_ret {
> + BPF_MTU_CHK_RET_SUCCESS, /* check and lookup successful */
> + BPF_MTU_CHK_RET_FRAG_NEEDED, /* fragmentation required to fwd */
> + BPF_MTU_CHK_RET_SEGS_TOOBIG, /* GSO re-segmentation needed to fwd */
> +};
> +
> enum bpf_task_fd_type {
> BPF_FD_TYPE_RAW_TRACEPOINT, /* tp name */
> BPF_FD_TYPE_TRACEPOINT, /* tp name */
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 25b137ffdced..d6125cfc49c3 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -5604,6 +5604,124 @@ static const struct bpf_func_proto
> bpf_skb_fib_lookup_proto = {
> .arg4_type = ARG_ANYTHING,
> };
> +static struct net_device *__dev_via_ifindex(struct net_device *dev_curr,
> + u32 ifindex)
> +{
> + struct net *netns = dev_net(dev_curr);
> +
> + /* Non-redirect use-cases can use ifindex=0 and save ifindex lookup */
> + if (ifindex == 0)
> + return dev_curr;
> +
> + return dev_get_by_index_rcu(netns, ifindex);
> +}
> +
> +BPF_CALL_5(bpf_skb_check_mtu, struct sk_buff *, skb,
> + u32, ifindex, u32 *, mtu_len, s32, len_diff, u64, flags)
> +{
> + int ret = BPF_MTU_CHK_RET_FRAG_NEEDED;
> + struct net_device *dev = skb->dev;
> + int len;
> + int mtu;
> +
> + if (flags & ~(BPF_MTU_CHK_SEGS))
> + return -EINVAL;
> +
> + dev = __dev_via_ifindex(dev, ifindex);
> + if (!dev)
> + return -ENODEV;
> +
> + mtu = READ_ONCE(dev->mtu);
> +
> + /* TC len is L2, remove L2-header as dev MTU is L3 size */
[..]
> + len = skb->len - ETH_HLEN;
Any reason not to do s/ETH_HLEN/dev->hard_header_len/ (or min_header_len?)
thought this patch?
next prev parent reply other threads:[~2020-12-03 18:26 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-20 16:18 [PATCH bpf-next V7 0/8] bpf: New approach for BPF MTU handling Jesper Dangaard Brouer
2020-11-20 16:18 ` [PATCH bpf-next V7 1/8] bpf: Remove MTU check in __bpf_skb_max_len Jesper Dangaard Brouer
2020-11-20 16:18 ` [PATCH bpf-next V7 2/8] bpf: fix bpf_fib_lookup helper MTU check for SKB ctx Jesper Dangaard Brouer
2020-12-02 21:44 ` Daniel Borkmann
2020-12-02 22:00 ` Daniel Borkmann
2020-11-20 16:18 ` [PATCH bpf-next V7 3/8] bpf: bpf_fib_lookup return MTU value as output when looked up Jesper Dangaard Brouer
2020-11-20 16:18 ` [PATCH bpf-next V7 4/8] bpf: add BPF-helper for MTU checking Jesper Dangaard Brouer
2020-12-03 18:25 ` sdf [this message]
2020-12-14 11:52 ` Jesper Dangaard Brouer
2020-11-20 16:18 ` [PATCH bpf-next V7 5/8] bpf: drop MTU check when doing TC-BPF redirect to ingress Jesper Dangaard Brouer
2020-11-20 16:18 ` [PATCH bpf-next V7 6/8] bpf: make it possible to identify BPF redirected SKBs Jesper Dangaard Brouer
2020-11-20 16:18 ` [PATCH bpf-next V7 7/8] selftests/bpf: use bpf_check_mtu in selftest test_cls_redirect Jesper Dangaard Brouer
2020-11-20 16:18 ` [PATCH bpf-next V7 8/8] bpf/selftests: activating bpf_check_mtu BPF-helper Jesper Dangaard Brouer
2020-11-20 21:50 ` Alexei Starovoitov
2020-11-21 7:41 ` Andrii Nakryiko
2020-11-24 14:33 ` Jesper Dangaard Brouer
2020-11-24 16:50 ` Yonghong Song
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