On Sun 08 Nov 2020 at 01:30, we...@ucloud.cn wrote:
> From: wenxu <we...@ucloud.cn>
>
> Currently kernel tc subsystem can do conntrack in act_ct. But when several
> fragment packets go through the act_ct, function tcf_ct_handle_fragments
> will defrag the packets to a big one. But the last action will redirect
> mirred to a device which maybe lead the reassembly big packet over the mtu
> of target device.
>
> This patch add support for a xmit hook to mirred, that gets executed before
> xmiting the packet. Then, when act_ct gets loaded, it configs that hook.
> The frag xmit hook maybe reused by other modules.
>
> Signed-off-by: wenxu <we...@ucloud.cn>
> ---
> v2: Fix the crash for act_frag module without load
> v3: modify the kconfig describe and put tcf_xmit_hook_is_enabled
> in the tcf_dev_queue_xmit, and xchg atomic for tcf_xmit_hook
> v4: using skb_protocol and fix line length exceeds 80 columns
> v5: no change
>
> include/net/act_api.h | 16 +++++
> net/sched/Kconfig | 13 ++++
> net/sched/Makefile | 1 +
> net/sched/act_api.c | 51 +++++++++++++++
> net/sched/act_ct.c | 7 +++
> net/sched/act_frag.c | 164
> +++++++++++++++++++++++++++++++++++++++++++++++++
> net/sched/act_mirred.c | 2 +-
> 7 files changed, 253 insertions(+), 1 deletion(-)
> create mode 100644 net/sched/act_frag.c
>
> diff --git a/include/net/act_api.h b/include/net/act_api.h
> index 8721492..403a618 100644
> --- a/include/net/act_api.h
> +++ b/include/net/act_api.h
> @@ -239,6 +239,22 @@ int tcf_action_check_ctrlact(int action, struct
> tcf_proto *tp,
> struct netlink_ext_ack *newchain);
> struct tcf_chain *tcf_action_set_ctrlact(struct tc_action *a, int action,
> struct tcf_chain *newchain);
> +
> +int tcf_dev_queue_xmit(struct sk_buff *skb, int (*xmit)(struct sk_buff
> *skb));
> +int tcf_set_xmit_hook(int (*xmit_hook)(struct sk_buff *skb,
> + int (*xmit)(struct sk_buff *skb)));
> +void tcf_clear_xmit_hook(void);
> +
> +#if IS_ENABLED(CONFIG_NET_ACT_FRAG)
> +int tcf_frag_xmit_hook(struct sk_buff *skb, int (*xmit)(struct sk_buff
> *skb));
> +#else
> +static inline int tcf_frag_xmit_hook(struct sk_buff *skb,
> + int (*xmit)(struct sk_buff *skb))
> +{
> + return 0;
> +}
> +#endif
> +
> #endif /* CONFIG_NET_CLS_ACT */
>
> static inline void tcf_action_stats_update(struct tc_action *a, u64 bytes,
> diff --git a/net/sched/Kconfig b/net/sched/Kconfig
> index a3b37d8..9a240c7 100644
> --- a/net/sched/Kconfig
> +++ b/net/sched/Kconfig
> @@ -974,9 +974,22 @@ config NET_ACT_TUNNEL_KEY
> To compile this code as a module, choose M here: the
> module will be called act_tunnel_key.
>
> +config NET_ACT_FRAG
> + tristate "Packet fragmentation"
> + depends on NET_CLS_ACT
> + help
> + Say Y here to allow fragmenting big packets when outputting
> + with the mirred action.
> +
> + If unsure, say N.
> +
> + To compile this code as a module, choose M here: the
> + module will be called act_frag.
> +
Just wondering, what is the motivation for putting the frag code into
standalone module? It doesn't implement usual act_* interface and is not
user-configurable. To me it looks like functionality that belongs to
act_api. Am I missing something?
> config NET_ACT_CT
> tristate "connection tracking tc action"
> depends on NET_CLS_ACT && NF_CONNTRACK && NF_NAT && NF_FLOW_TABLE
> + depends on NET_ACT_FRAG
> help
> Say Y here to allow sending the packets to conntrack module.
>
> diff --git a/net/sched/Makefile b/net/sched/Makefile
> index 66bbf9a..c146186 100644
> --- a/net/sched/Makefile
> +++ b/net/sched/Makefile
> @@ -29,6 +29,7 @@ obj-$(CONFIG_NET_IFE_SKBMARK) += act_meta_mark.o
> obj-$(CONFIG_NET_IFE_SKBPRIO) += act_meta_skbprio.o
> obj-$(CONFIG_NET_IFE_SKBTCINDEX) += act_meta_skbtcindex.o
> obj-$(CONFIG_NET_ACT_TUNNEL_KEY)+= act_tunnel_key.o
> +obj-$(CONFIG_NET_ACT_FRAG) += act_frag.o
> obj-$(CONFIG_NET_ACT_CT) += act_ct.o
> obj-$(CONFIG_NET_ACT_GATE) += act_gate.o
> obj-$(CONFIG_NET_SCH_FIFO) += sch_fifo.o
> diff --git a/net/sched/act_api.c b/net/sched/act_api.c
> index f66417d..e7b501c 100644
> --- a/net/sched/act_api.c
> +++ b/net/sched/act_api.c
> @@ -22,6 +22,57 @@
> #include <net/act_api.h>
> #include <net/netlink.h>
>
> +static int (*tcf_xmit_hook)(struct sk_buff *skb,
> + int (*xmit)(struct sk_buff *skb));
> +static DEFINE_STATIC_KEY_FALSE(tcf_xmit_hook_in_use);
> +
> +static void tcf_inc_xmit_hook(void)
> +{
> + static_branch_inc(&tcf_xmit_hook_in_use);
> +}
> +
> +static void tcf_dec_xmit_hook(void)
> +{
> + static_branch_dec(&tcf_xmit_hook_in_use);
> +}
> +
> +static bool tcf_xmit_hook_enabled(void)
> +{
> + return static_branch_unlikely(&tcf_xmit_hook_in_use);
> +}
> +
> +int tcf_set_xmit_hook(int (*xmit_hook)(struct sk_buff *skb,
> + int (*xmit)(struct sk_buff *skb)))
> +{
> + if (!tcf_xmit_hook_enabled())
> + xchg(&tcf_xmit_hook, xmit_hook);
Marcelo, why did you suggest to use atomic operations to change
tcf_xmit_hook variable? It is not obvious to me after reading the code.
> + else if (xmit_hook != tcf_xmit_hook)
> + return -EBUSY;
> +
> + tcf_inc_xmit_hook();
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(tcf_set_xmit_hook);
> +
> +void tcf_clear_xmit_hook(void)
> +{
> + tcf_dec_xmit_hook();
> +
> + if (!tcf_xmit_hook_enabled())
> + xchg(&tcf_xmit_hook, NULL);
> +}
> +EXPORT_SYMBOL_GPL(tcf_clear_xmit_hook);
> +
> +int tcf_dev_queue_xmit(struct sk_buff *skb, int (*xmit)(struct sk_buff *skb))
> +{
> + if (tcf_xmit_hook_enabled())
Okay, so what happens here if tcf_xmit_hook is disabled concurrently? If
we get here from some rule that doesn't involve act_ct but uses
act_mirred and act_ct is concurrently removed decrementing last
reference to static branch and setting tcf_xmit_hook to NULL?
> + return tcf_xmit_hook(skb, xmit);
> + else
> + return xmit(skb);
> +}
> +EXPORT_SYMBOL_GPL(tcf_dev_queue_xmit);
> +
> static void tcf_action_goto_chain_exec(const struct tc_action *a,
> struct tcf_result *res)
> {
> diff --git a/net/sched/act_ct.c b/net/sched/act_ct.c
> index 9c79fb9..dff3c40 100644
> --- a/net/sched/act_ct.c
> +++ b/net/sched/act_ct.c
> @@ -1541,8 +1541,14 @@ static int __init ct_init_module(void)
> if (err)
> goto err_register;
>
> + err = tcf_set_xmit_hook(tcf_frag_xmit_hook);
> + if (err)
> + goto err_action;
> +
> return 0;
>
> +err_action:
> + tcf_unregister_action(&act_ct_ops, &ct_net_ops);
> err_register:
> tcf_ct_flow_tables_uninit();
> err_tbl_init:
> @@ -1552,6 +1558,7 @@ static int __init ct_init_module(void)
>
> static void __exit ct_cleanup_module(void)
> {
> + tcf_clear_xmit_hook();
> tcf_unregister_action(&act_ct_ops, &ct_net_ops);
> tcf_ct_flow_tables_uninit();
> destroy_workqueue(act_ct_wq);
> diff --git a/net/sched/act_frag.c b/net/sched/act_frag.c
> new file mode 100644
> index 0000000..3a7ab92
> --- /dev/null
> +++ b/net/sched/act_frag.c
> @@ -0,0 +1,164 @@
> +// SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB
> +#include <net/netlink.h>
> +#include <net/act_api.h>
> +#include <net/dst.h>
> +#include <net/ip.h>
> +#include <net/ip6_fib.h>
> +
> +struct tcf_frag_data {
> + unsigned long dst;
> + struct qdisc_skb_cb cb;
> + __be16 inner_protocol;
> + u16 vlan_tci;
> + __be16 vlan_proto;
> + unsigned int l2_len;
> + u8 l2_data[VLAN_ETH_HLEN];
> + int (*xmit)(struct sk_buff *skb);
> +};
> +
> +static DEFINE_PER_CPU(struct tcf_frag_data, tcf_frag_data_storage);
> +
> +static int tcf_frag_xmit(struct net *net, struct sock *sk, struct sk_buff
> *skb)
> +{
> + struct tcf_frag_data *data = this_cpu_ptr(&tcf_frag_data_storage);
> +
> + if (skb_cow_head(skb, data->l2_len) < 0) {
> + kfree_skb(skb);
> + return -ENOMEM;
> + }
> +
> + __skb_dst_copy(skb, data->dst);
> + *qdisc_skb_cb(skb) = data->cb;
> + skb->inner_protocol = data->inner_protocol;
> + if (data->vlan_tci & VLAN_CFI_MASK)
> + __vlan_hwaccel_put_tag(skb, data->vlan_proto,
> + data->vlan_tci & ~VLAN_CFI_MASK);
> + else
> + __vlan_hwaccel_clear_tag(skb);
> +
> + /* Reconstruct the MAC header. */
> + skb_push(skb, data->l2_len);
> + memcpy(skb->data, &data->l2_data, data->l2_len);
> + skb_postpush_rcsum(skb, skb->data, data->l2_len);
> + skb_reset_mac_header(skb);
> +
> + data->xmit(skb);
> +
> + return 0;
> +}
> +
> +static void tcf_frag_prepare_frag(struct sk_buff *skb,
> + int (*xmit)(struct sk_buff *skb))
> +{
> + unsigned int hlen = skb_network_offset(skb);
> + struct tcf_frag_data *data;
> +
> + data = this_cpu_ptr(&tcf_frag_data_storage);
> + data->dst = skb->_skb_refdst;
> + data->cb = *qdisc_skb_cb(skb);
> + data->xmit = xmit;
> + data->inner_protocol = skb->inner_protocol;
> + if (skb_vlan_tag_present(skb))
> + data->vlan_tci = skb_vlan_tag_get(skb) | VLAN_CFI_MASK;
> + else
> + data->vlan_tci = 0;
> + data->vlan_proto = skb->vlan_proto;
> + data->l2_len = hlen;
> + memcpy(&data->l2_data, skb->data, hlen);
> +
> + memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
> + skb_pull(skb, hlen);
> +}
> +
> +static unsigned int
> +tcf_frag_dst_get_mtu(const struct dst_entry *dst)
> +{
> + return dst->dev->mtu;
> +}
> +
> +static struct dst_ops tcf_frag_dst_ops = {
> + .family = AF_UNSPEC,
> + .mtu = tcf_frag_dst_get_mtu,
> +};
> +
> +static int tcf_fragment(struct net *net, struct sk_buff *skb,
> + u16 mru, int (*xmit)(struct sk_buff *skb))
> +{
> + if (skb_network_offset(skb) > VLAN_ETH_HLEN) {
> + net_warn_ratelimited("L2 header too long to fragment\n");
> + goto err;
> + }
> +
> + if (skb_protocol(skb, true) == htons(ETH_P_IP)) {
> + struct dst_entry tcf_frag_dst;
> + unsigned long orig_dst;
> +
> + tcf_frag_prepare_frag(skb, xmit);
> + dst_init(&tcf_frag_dst, &tcf_frag_dst_ops, NULL, 1,
> + DST_OBSOLETE_NONE, DST_NOCOUNT);
> + tcf_frag_dst.dev = skb->dev;
> +
> + orig_dst = skb->_skb_refdst;
> + skb_dst_set_noref(skb, &tcf_frag_dst);
> + IPCB(skb)->frag_max_size = mru;
> +
> + ip_do_fragment(net, skb->sk, skb, tcf_frag_xmit);
> + refdst_drop(orig_dst);
> + } else if (skb_protocol(skb, true) == htons(ETH_P_IPV6)) {
> + unsigned long orig_dst;
> + struct rt6_info tcf_frag_rt;
> +
> + tcf_frag_prepare_frag(skb, xmit);
> + memset(&tcf_frag_rt, 0, sizeof(tcf_frag_rt));
> + dst_init(&tcf_frag_rt.dst, &tcf_frag_dst_ops, NULL, 1,
> + DST_OBSOLETE_NONE, DST_NOCOUNT);
> + tcf_frag_rt.dst.dev = skb->dev;
> +
> + orig_dst = skb->_skb_refdst;
> + skb_dst_set_noref(skb, &tcf_frag_rt.dst);
> + IP6CB(skb)->frag_max_size = mru;
> +
> + ipv6_stub->ipv6_fragment(net, skb->sk, skb, tcf_frag_xmit);
> + refdst_drop(orig_dst);
> + } else {
> + net_warn_ratelimited("Fail frag %s: eth=%x, MRU=%d, MTU=%d\n",
> + netdev_name(skb->dev),
> + ntohs(skb_protocol(skb, true)), mru,
> + skb->dev->mtu);
> + goto err;
> + }
> +
> + qdisc_skb_cb(skb)->mru = 0;
> + return 0;
> +err:
> + kfree_skb(skb);
> + return -1;
> +}
> +
> +int tcf_frag_xmit_hook(struct sk_buff *skb, int (*xmit)(struct sk_buff *skb))
> +{
> + u16 mru = qdisc_skb_cb(skb)->mru;
> + int err;
> +
> + if (mru && skb->len > mru + skb->dev->hard_header_len)
> + err = tcf_fragment(dev_net(skb->dev), skb, mru, xmit);
> + else
> + err = xmit(skb);
> +
> + return err;
> +}
> +EXPORT_SYMBOL_GPL(tcf_frag_xmit_hook);
> +
> +static int __init frag_init_module(void)
> +{
> + return 0;
> +}
> +
> +static void __exit frag_cleanup_module(void)
> +{
> +}
> +
> +module_init(frag_init_module);
> +module_exit(frag_cleanup_module);
> +MODULE_AUTHOR("wenxu <we...@ucloud.cn>");
> +MODULE_LICENSE("GPL v2");
> diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
> index 17d0095..7153c67 100644
> --- a/net/sched/act_mirred.c
> +++ b/net/sched/act_mirred.c
> @@ -210,7 +210,7 @@ static int tcf_mirred_forward(bool want_ingress, struct
> sk_buff *skb)
> int err;
>
> if (!want_ingress)
> - err = dev_queue_xmit(skb);
> + err = tcf_dev_queue_xmit(skb, dev_queue_xmit);
> else
> err = netif_receive_skb(skb);
