![Herbert Xu](/assets/img/avatar_default.png)
Up until now cls_cgroup has relied on fetching the classid out of the current executing thread. This runs into trouble when a packet processing is delayed in which case it may execute out of another thread's context. Furthermore, even when a packet is not delayed we may fail to classify it if soft IRQs have been disabled, because this scenario is indistinguishable from one where a packet unrelated to the current thread is processed by a real soft IRQ. In fact, the current semantics is inherently broken, as a single skb may be constructed out of the writes of two different tasks. A different manifestation of this problem is when the TCP stack transmits in response of an incoming ACK. This is currently unclassified. As we already have a concept of packet ownership for accounting purposes in the skb->sk pointer, this is a natural place to store the classid in a persistent manner. This patch adds the cls_cgroup classid in struct sock, filling up an existing hole on 64-bit :) The value is set at socket creation time. So all sockets created via socket(2) automatically gains the ID of the thread creating it. Whenever another process touches the socket by either reading or writing to it, we will change the socket classid to that of the process if it has a valid (non-zero) classid. For sockets created on inbound connections through accept(2), we inherit the classid of the original listening socket through sk_clone, possibly preceding the actual accept(2) call. In order to minimise risks, I have not made this the authoritative classid. For now it is only used as a backup when we execute with soft IRQs disabled. Once we're completely happy with its semantics we can use it as the sole classid. Footnote: I have rearranged the error path on cls_group module creation. If we didn't do this, then there is a window where someone could create a tc rule using cls_group before the cgroup subsystem has been registered. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>
328 lines
7.3 KiB
C
328 lines
7.3 KiB
C
/*
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* net/sched/cls_cgroup.c Control Group Classifier
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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* Authors: Thomas Graf <tgraf@suug.ch>
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*/
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/types.h>
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#include <linux/string.h>
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#include <linux/errno.h>
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#include <linux/skbuff.h>
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#include <linux/cgroup.h>
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#include <linux/rcupdate.h>
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#include <net/rtnetlink.h>
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#include <net/pkt_cls.h>
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#include <net/sock.h>
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#include <net/cls_cgroup.h>
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static struct cgroup_subsys_state *cgrp_create(struct cgroup_subsys *ss,
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struct cgroup *cgrp);
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static void cgrp_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp);
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static int cgrp_populate(struct cgroup_subsys *ss, struct cgroup *cgrp);
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struct cgroup_subsys net_cls_subsys = {
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.name = "net_cls",
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.create = cgrp_create,
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.destroy = cgrp_destroy,
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.populate = cgrp_populate,
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#ifdef CONFIG_NET_CLS_CGROUP
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.subsys_id = net_cls_subsys_id,
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#else
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#define net_cls_subsys_id net_cls_subsys.subsys_id
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#endif
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.module = THIS_MODULE,
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};
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static inline struct cgroup_cls_state *cgrp_cls_state(struct cgroup *cgrp)
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{
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return container_of(cgroup_subsys_state(cgrp, net_cls_subsys_id),
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struct cgroup_cls_state, css);
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}
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static inline struct cgroup_cls_state *task_cls_state(struct task_struct *p)
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{
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return container_of(task_subsys_state(p, net_cls_subsys_id),
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struct cgroup_cls_state, css);
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}
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static struct cgroup_subsys_state *cgrp_create(struct cgroup_subsys *ss,
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struct cgroup *cgrp)
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{
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struct cgroup_cls_state *cs;
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if (!(cs = kzalloc(sizeof(*cs), GFP_KERNEL)))
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return ERR_PTR(-ENOMEM);
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if (cgrp->parent)
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cs->classid = cgrp_cls_state(cgrp->parent)->classid;
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return &cs->css;
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}
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static void cgrp_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp)
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{
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kfree(cgrp_cls_state(cgrp));
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}
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static u64 read_classid(struct cgroup *cgrp, struct cftype *cft)
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{
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return cgrp_cls_state(cgrp)->classid;
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}
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static int write_classid(struct cgroup *cgrp, struct cftype *cft, u64 value)
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{
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cgrp_cls_state(cgrp)->classid = (u32) value;
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return 0;
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}
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static struct cftype ss_files[] = {
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{
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.name = "classid",
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.read_u64 = read_classid,
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.write_u64 = write_classid,
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},
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};
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static int cgrp_populate(struct cgroup_subsys *ss, struct cgroup *cgrp)
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{
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return cgroup_add_files(cgrp, ss, ss_files, ARRAY_SIZE(ss_files));
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}
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struct cls_cgroup_head
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{
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u32 handle;
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struct tcf_exts exts;
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struct tcf_ematch_tree ematches;
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};
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static int cls_cgroup_classify(struct sk_buff *skb, struct tcf_proto *tp,
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struct tcf_result *res)
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{
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struct cls_cgroup_head *head = tp->root;
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u32 classid;
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rcu_read_lock();
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classid = task_cls_state(current)->classid;
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rcu_read_unlock();
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/*
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* Due to the nature of the classifier it is required to ignore all
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* packets originating from softirq context as accessing `current'
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* would lead to false results.
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*
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* This test assumes that all callers of dev_queue_xmit() explicitely
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* disable bh. Knowing this, it is possible to detect softirq based
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* calls by looking at the number of nested bh disable calls because
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* softirqs always disables bh.
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*/
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if (softirq_count() != SOFTIRQ_OFFSET) {
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/* If there is an sk_classid we'll use that. */
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if (!skb->sk)
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return -1;
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classid = skb->sk->sk_classid;
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}
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if (!classid)
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return -1;
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if (!tcf_em_tree_match(skb, &head->ematches, NULL))
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return -1;
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res->classid = classid;
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res->class = 0;
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return tcf_exts_exec(skb, &head->exts, res);
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}
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static unsigned long cls_cgroup_get(struct tcf_proto *tp, u32 handle)
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{
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return 0UL;
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}
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static void cls_cgroup_put(struct tcf_proto *tp, unsigned long f)
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{
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}
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static int cls_cgroup_init(struct tcf_proto *tp)
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{
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return 0;
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}
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static const struct tcf_ext_map cgroup_ext_map = {
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.action = TCA_CGROUP_ACT,
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.police = TCA_CGROUP_POLICE,
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};
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static const struct nla_policy cgroup_policy[TCA_CGROUP_MAX + 1] = {
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[TCA_CGROUP_EMATCHES] = { .type = NLA_NESTED },
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};
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static int cls_cgroup_change(struct tcf_proto *tp, unsigned long base,
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u32 handle, struct nlattr **tca,
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unsigned long *arg)
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{
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struct nlattr *tb[TCA_CGROUP_MAX+1];
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struct cls_cgroup_head *head = tp->root;
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struct tcf_ematch_tree t;
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struct tcf_exts e;
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int err;
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if (!tca[TCA_OPTIONS])
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return -EINVAL;
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if (head == NULL) {
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if (!handle)
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return -EINVAL;
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head = kzalloc(sizeof(*head), GFP_KERNEL);
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if (head == NULL)
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return -ENOBUFS;
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head->handle = handle;
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tcf_tree_lock(tp);
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tp->root = head;
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tcf_tree_unlock(tp);
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}
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if (handle != head->handle)
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return -ENOENT;
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err = nla_parse_nested(tb, TCA_CGROUP_MAX, tca[TCA_OPTIONS],
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cgroup_policy);
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if (err < 0)
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return err;
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err = tcf_exts_validate(tp, tb, tca[TCA_RATE], &e, &cgroup_ext_map);
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if (err < 0)
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return err;
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err = tcf_em_tree_validate(tp, tb[TCA_CGROUP_EMATCHES], &t);
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if (err < 0)
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return err;
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tcf_exts_change(tp, &head->exts, &e);
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tcf_em_tree_change(tp, &head->ematches, &t);
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return 0;
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}
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static void cls_cgroup_destroy(struct tcf_proto *tp)
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{
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struct cls_cgroup_head *head = tp->root;
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if (head) {
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tcf_exts_destroy(tp, &head->exts);
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tcf_em_tree_destroy(tp, &head->ematches);
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kfree(head);
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}
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}
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static int cls_cgroup_delete(struct tcf_proto *tp, unsigned long arg)
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{
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return -EOPNOTSUPP;
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}
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static void cls_cgroup_walk(struct tcf_proto *tp, struct tcf_walker *arg)
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{
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struct cls_cgroup_head *head = tp->root;
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if (arg->count < arg->skip)
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goto skip;
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if (arg->fn(tp, (unsigned long) head, arg) < 0) {
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arg->stop = 1;
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return;
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}
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skip:
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arg->count++;
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}
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static int cls_cgroup_dump(struct tcf_proto *tp, unsigned long fh,
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struct sk_buff *skb, struct tcmsg *t)
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{
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struct cls_cgroup_head *head = tp->root;
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unsigned char *b = skb_tail_pointer(skb);
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struct nlattr *nest;
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t->tcm_handle = head->handle;
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nest = nla_nest_start(skb, TCA_OPTIONS);
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if (nest == NULL)
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goto nla_put_failure;
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if (tcf_exts_dump(skb, &head->exts, &cgroup_ext_map) < 0 ||
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tcf_em_tree_dump(skb, &head->ematches, TCA_CGROUP_EMATCHES) < 0)
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goto nla_put_failure;
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nla_nest_end(skb, nest);
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if (tcf_exts_dump_stats(skb, &head->exts, &cgroup_ext_map) < 0)
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goto nla_put_failure;
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return skb->len;
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nla_put_failure:
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nlmsg_trim(skb, b);
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return -1;
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}
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static struct tcf_proto_ops cls_cgroup_ops __read_mostly = {
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.kind = "cgroup",
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.init = cls_cgroup_init,
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.change = cls_cgroup_change,
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.classify = cls_cgroup_classify,
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.destroy = cls_cgroup_destroy,
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.get = cls_cgroup_get,
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.put = cls_cgroup_put,
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.delete = cls_cgroup_delete,
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.walk = cls_cgroup_walk,
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.dump = cls_cgroup_dump,
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.owner = THIS_MODULE,
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};
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static int __init init_cgroup_cls(void)
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{
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int ret;
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ret = cgroup_load_subsys(&net_cls_subsys);
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if (ret)
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goto out;
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#ifndef CONFIG_NET_CLS_CGROUP
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/* We can't use rcu_assign_pointer because this is an int. */
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smp_wmb();
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net_cls_subsys_id = net_cls_subsys.subsys_id;
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#endif
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ret = register_tcf_proto_ops(&cls_cgroup_ops);
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if (ret)
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cgroup_unload_subsys(&net_cls_subsys);
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out:
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return ret;
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}
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static void __exit exit_cgroup_cls(void)
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{
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unregister_tcf_proto_ops(&cls_cgroup_ops);
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#ifndef CONFIG_NET_CLS_CGROUP
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net_cls_subsys_id = -1;
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synchronize_rcu();
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#endif
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cgroup_unload_subsys(&net_cls_subsys);
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}
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module_init(init_cgroup_cls);
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module_exit(exit_cgroup_cls);
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MODULE_LICENSE("GPL");
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