![John Fastabend](/assets/img/avatar_default.png)
Using the tcf_proto pointer 'tp' from inside the classifiers callback is not valid because it may have been cleaned up by another call_rcu occuring on another CPU. 'tp' is currently being used by tcf_unbind_filter() in this patch we move instances of tcf_unbind_filter outside of the call_rcu() context. This is safe to do because any running schedulers will either read the valid class field or it will be zeroed. And all schedulers today when the class is 0 do a lookup using the same call used by the tcf_exts_bind(). So even if we have a running classifier hit the null class pointer it will do a lookup and get to the same result. This is particularly fragile at the moment because the only way to verify this is to audit the schedulers call sites. Reported-by: Cong Wang <xiyou.wangconf@gmail.com> Signed-off-by: John Fastabend <john.r.fastabend@intel.com> Acked-by: Cong Wang <cwang@twopensource.com> Signed-off-by: David S. Miller <davem@davemloft.net>
385 lines
8.4 KiB
C
385 lines
8.4 KiB
C
/*
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* Berkeley Packet Filter based traffic classifier
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*
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* Might be used to classify traffic through flexible, user-defined and
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* possibly JIT-ed BPF filters for traffic control as an alternative to
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* ematches.
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*
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* (C) 2013 Daniel Borkmann <dborkman@redhat.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/module.h>
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#include <linux/types.h>
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#include <linux/skbuff.h>
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#include <linux/filter.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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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Daniel Borkmann <dborkman@redhat.com>");
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MODULE_DESCRIPTION("TC BPF based classifier");
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struct cls_bpf_head {
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struct list_head plist;
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u32 hgen;
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struct rcu_head rcu;
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};
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struct cls_bpf_prog {
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struct bpf_prog *filter;
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struct sock_filter *bpf_ops;
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struct tcf_exts exts;
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struct tcf_result res;
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struct list_head link;
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u32 handle;
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u16 bpf_len;
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struct tcf_proto *tp;
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struct rcu_head rcu;
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};
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static const struct nla_policy bpf_policy[TCA_BPF_MAX + 1] = {
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[TCA_BPF_CLASSID] = { .type = NLA_U32 },
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[TCA_BPF_OPS_LEN] = { .type = NLA_U16 },
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[TCA_BPF_OPS] = { .type = NLA_BINARY,
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.len = sizeof(struct sock_filter) * BPF_MAXINSNS },
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};
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static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp,
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struct tcf_result *res)
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{
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struct cls_bpf_head *head = rcu_dereference_bh(tp->root);
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struct cls_bpf_prog *prog;
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int ret;
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list_for_each_entry_rcu(prog, &head->plist, link) {
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int filter_res = BPF_PROG_RUN(prog->filter, skb);
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if (filter_res == 0)
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continue;
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*res = prog->res;
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if (filter_res != -1)
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res->classid = filter_res;
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ret = tcf_exts_exec(skb, &prog->exts, res);
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if (ret < 0)
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continue;
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return ret;
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}
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return -1;
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}
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static int cls_bpf_init(struct tcf_proto *tp)
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{
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struct cls_bpf_head *head;
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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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INIT_LIST_HEAD_RCU(&head->plist);
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rcu_assign_pointer(tp->root, head);
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return 0;
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}
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static void cls_bpf_delete_prog(struct tcf_proto *tp, struct cls_bpf_prog *prog)
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{
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tcf_exts_destroy(&prog->exts);
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bpf_prog_destroy(prog->filter);
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kfree(prog->bpf_ops);
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kfree(prog);
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}
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static void __cls_bpf_delete_prog(struct rcu_head *rcu)
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{
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struct cls_bpf_prog *prog = container_of(rcu, struct cls_bpf_prog, rcu);
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cls_bpf_delete_prog(prog->tp, prog);
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}
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static int cls_bpf_delete(struct tcf_proto *tp, unsigned long arg)
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{
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struct cls_bpf_head *head = rtnl_dereference(tp->root);
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struct cls_bpf_prog *prog, *todel = (struct cls_bpf_prog *) arg;
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list_for_each_entry(prog, &head->plist, link) {
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if (prog == todel) {
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list_del_rcu(&prog->link);
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tcf_unbind_filter(tp, &prog->res);
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call_rcu(&prog->rcu, __cls_bpf_delete_prog);
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return 0;
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}
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}
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return -ENOENT;
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}
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static void cls_bpf_destroy(struct tcf_proto *tp)
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{
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struct cls_bpf_head *head = rtnl_dereference(tp->root);
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struct cls_bpf_prog *prog, *tmp;
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list_for_each_entry_safe(prog, tmp, &head->plist, link) {
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list_del_rcu(&prog->link);
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tcf_unbind_filter(tp, &prog->res);
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call_rcu(&prog->rcu, __cls_bpf_delete_prog);
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}
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RCU_INIT_POINTER(tp->root, NULL);
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kfree_rcu(head, rcu);
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}
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static unsigned long cls_bpf_get(struct tcf_proto *tp, u32 handle)
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{
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struct cls_bpf_head *head = rtnl_dereference(tp->root);
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struct cls_bpf_prog *prog;
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unsigned long ret = 0UL;
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if (head == NULL)
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return 0UL;
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list_for_each_entry_rcu(prog, &head->plist, link) {
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if (prog->handle == handle) {
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ret = (unsigned long) prog;
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break;
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}
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}
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return ret;
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}
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static void cls_bpf_put(struct tcf_proto *tp, unsigned long f)
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{
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}
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static int cls_bpf_modify_existing(struct net *net, struct tcf_proto *tp,
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struct cls_bpf_prog *prog,
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unsigned long base, struct nlattr **tb,
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struct nlattr *est, bool ovr)
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{
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struct sock_filter *bpf_ops;
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struct tcf_exts exts;
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struct sock_fprog_kern tmp;
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struct bpf_prog *fp;
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u16 bpf_size, bpf_len;
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u32 classid;
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int ret;
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if (!tb[TCA_BPF_OPS_LEN] || !tb[TCA_BPF_OPS] || !tb[TCA_BPF_CLASSID])
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return -EINVAL;
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tcf_exts_init(&exts, TCA_BPF_ACT, TCA_BPF_POLICE);
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ret = tcf_exts_validate(net, tp, tb, est, &exts, ovr);
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if (ret < 0)
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return ret;
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classid = nla_get_u32(tb[TCA_BPF_CLASSID]);
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bpf_len = nla_get_u16(tb[TCA_BPF_OPS_LEN]);
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if (bpf_len > BPF_MAXINSNS || bpf_len == 0) {
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ret = -EINVAL;
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goto errout;
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}
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bpf_size = bpf_len * sizeof(*bpf_ops);
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bpf_ops = kzalloc(bpf_size, GFP_KERNEL);
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if (bpf_ops == NULL) {
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ret = -ENOMEM;
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goto errout;
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}
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memcpy(bpf_ops, nla_data(tb[TCA_BPF_OPS]), bpf_size);
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tmp.len = bpf_len;
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tmp.filter = bpf_ops;
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ret = bpf_prog_create(&fp, &tmp);
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if (ret)
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goto errout_free;
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prog->bpf_len = bpf_len;
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prog->bpf_ops = bpf_ops;
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prog->filter = fp;
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prog->res.classid = classid;
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tcf_bind_filter(tp, &prog->res, base);
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tcf_exts_change(tp, &prog->exts, &exts);
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return 0;
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errout_free:
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kfree(bpf_ops);
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errout:
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tcf_exts_destroy(&exts);
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return ret;
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}
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static u32 cls_bpf_grab_new_handle(struct tcf_proto *tp,
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struct cls_bpf_head *head)
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{
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unsigned int i = 0x80000000;
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do {
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if (++head->hgen == 0x7FFFFFFF)
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head->hgen = 1;
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} while (--i > 0 && cls_bpf_get(tp, head->hgen));
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if (i == 0)
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pr_err("Insufficient number of handles\n");
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return i;
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}
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static int cls_bpf_change(struct net *net, struct sk_buff *in_skb,
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struct tcf_proto *tp, unsigned long base,
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u32 handle, struct nlattr **tca,
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unsigned long *arg, bool ovr)
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{
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struct cls_bpf_head *head = rtnl_dereference(tp->root);
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struct cls_bpf_prog *oldprog = (struct cls_bpf_prog *) *arg;
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struct nlattr *tb[TCA_BPF_MAX + 1];
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struct cls_bpf_prog *prog;
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int ret;
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if (tca[TCA_OPTIONS] == NULL)
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return -EINVAL;
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ret = nla_parse_nested(tb, TCA_BPF_MAX, tca[TCA_OPTIONS], bpf_policy);
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if (ret < 0)
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return ret;
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prog = kzalloc(sizeof(*prog), GFP_KERNEL);
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if (!prog)
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return -ENOBUFS;
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tcf_exts_init(&prog->exts, TCA_BPF_ACT, TCA_BPF_POLICE);
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if (oldprog) {
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if (handle && oldprog->handle != handle) {
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ret = -EINVAL;
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goto errout;
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}
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}
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if (handle == 0)
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prog->handle = cls_bpf_grab_new_handle(tp, head);
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else
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prog->handle = handle;
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if (prog->handle == 0) {
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ret = -EINVAL;
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goto errout;
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}
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ret = cls_bpf_modify_existing(net, tp, prog, base, tb, tca[TCA_RATE], ovr);
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if (ret < 0)
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goto errout;
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if (oldprog) {
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list_replace_rcu(&prog->link, &oldprog->link);
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tcf_unbind_filter(tp, &oldprog->res);
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call_rcu(&oldprog->rcu, __cls_bpf_delete_prog);
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} else {
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list_add_rcu(&prog->link, &head->plist);
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}
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*arg = (unsigned long) prog;
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return 0;
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errout:
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kfree(prog);
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return ret;
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}
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static int cls_bpf_dump(struct net *net, struct tcf_proto *tp, unsigned long fh,
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struct sk_buff *skb, struct tcmsg *tm)
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{
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struct cls_bpf_prog *prog = (struct cls_bpf_prog *) fh;
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struct nlattr *nest, *nla;
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if (prog == NULL)
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return skb->len;
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tm->tcm_handle = prog->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 (nla_put_u32(skb, TCA_BPF_CLASSID, prog->res.classid))
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goto nla_put_failure;
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if (nla_put_u16(skb, TCA_BPF_OPS_LEN, prog->bpf_len))
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goto nla_put_failure;
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nla = nla_reserve(skb, TCA_BPF_OPS, prog->bpf_len *
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sizeof(struct sock_filter));
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if (nla == NULL)
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goto nla_put_failure;
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memcpy(nla_data(nla), prog->bpf_ops, nla_len(nla));
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if (tcf_exts_dump(skb, &prog->exts) < 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, &prog->exts) < 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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nla_nest_cancel(skb, nest);
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return -1;
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}
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static void cls_bpf_walk(struct tcf_proto *tp, struct tcf_walker *arg)
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{
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struct cls_bpf_head *head = rtnl_dereference(tp->root);
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struct cls_bpf_prog *prog;
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list_for_each_entry_rcu(prog, &head->plist, link) {
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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) prog, arg) < 0) {
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arg->stop = 1;
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break;
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}
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skip:
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arg->count++;
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}
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}
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static struct tcf_proto_ops cls_bpf_ops __read_mostly = {
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.kind = "bpf",
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.owner = THIS_MODULE,
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.classify = cls_bpf_classify,
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.init = cls_bpf_init,
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.destroy = cls_bpf_destroy,
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.get = cls_bpf_get,
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.put = cls_bpf_put,
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.change = cls_bpf_change,
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.delete = cls_bpf_delete,
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.walk = cls_bpf_walk,
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.dump = cls_bpf_dump,
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};
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static int __init cls_bpf_init_mod(void)
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{
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return register_tcf_proto_ops(&cls_bpf_ops);
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}
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static void __exit cls_bpf_exit_mod(void)
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{
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unregister_tcf_proto_ops(&cls_bpf_ops);
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}
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module_init(cls_bpf_init_mod);
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module_exit(cls_bpf_exit_mod);
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