Commit 304e0242 authored by Cong Wang's avatar Cong Wang Committed by David S. Miller
Browse files

net_sched: add a temporary refcnt for struct tcindex_data 



Although we intentionally use an ordered workqueue for all tc
filter works, the ordering is not guaranteed by RCU work,
given that tcf_queue_work() is esstenially a call_rcu().

This problem is demostrated by Thomas:

  CPU 0:
    tcf_queue_work()
      tcf_queue_work(&r->rwork, tcindex_destroy_rexts_work);

  -> Migration to CPU 1

  CPU 1:
     tcf_queue_work(&p->rwork, tcindex_destroy_work);

so the 2nd work could be queued before the 1st one, which leads
to a free-after-free.

Enforcing this order in RCU work is hard as it requires to change
RCU code too. Fortunately we can workaround this problem in tcindex
filter by taking a temporary refcnt, we only refcnt it right before
we begin to destroy it. This simplifies the code a lot as a full
refcnt requires much more changes in tcindex_set_parms().

Reported-by: default avatar <syzbot+46f513c3033d592409d2@syzkaller.appspotmail.com>
Fixes: 3d210534 ("net_sched: fix a race condition in tcindex_destroy()")
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: default avatarCong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1a323ea5

net/sched/cls_tcindex.c

+38 −6
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
#include <linux/skbuff.h>

#include <linux/errno.h>

#include <linux/slab.h>

#include <linux/refcount.h>

#include <net/act_api.h>

#include <net/netlink.h>

#include <net/pkt_cls.h>
@@ -26,9 +27,12 @@ 
#define DEFAULT_HASH_SIZE	64	/* optimized for diffserv */





struct tcindex_data;



struct tcindex_filter_result {

	struct tcf_exts		exts;

	struct tcf_result	res;

	struct tcindex_data	*p;

	struct rcu_work		rwork;

};
@@ -49,6 +53,7 @@ struct tcindex_data { 
	u32 hash;		/* hash table size; 0 if undefined */

	u32 alloc_hash;		/* allocated size */

	u32 fall_through;	/* 0: only classify if explicit match */

	refcount_t refcnt;	/* a temporary refcnt for perfect hash */

	struct rcu_work rwork;

};
@@ -57,6 +62,20 @@ static inline int tcindex_filter_is_set(struct tcindex_filter_result *r) 
	return tcf_exts_has_actions(&r->exts) || r->res.classid;

}



static void tcindex_data_get(struct tcindex_data *p)

{

	refcount_inc(&p->refcnt);

}



static void tcindex_data_put(struct tcindex_data *p)

{

	if (refcount_dec_and_test(&p->refcnt)) {

		kfree(p->perfect);

		kfree(p->h);

		kfree(p);

	}

}



static struct tcindex_filter_result *tcindex_lookup(struct tcindex_data *p,

						    u16 key)

{
@@ -141,6 +160,7 @@ static void __tcindex_destroy_rexts(struct tcindex_filter_result *r) 
{

	tcf_exts_destroy(&r->exts);

	tcf_exts_put_net(&r->exts);

	tcindex_data_put(r->p);

}



static void tcindex_destroy_rexts_work(struct work_struct *work)
@@ -212,6 +232,8 @@ found: 
		else

			__tcindex_destroy_fexts(f);

	} else {

		tcindex_data_get(p);



		if (tcf_exts_get_net(&r->exts))

			tcf_queue_work(&r->rwork, tcindex_destroy_rexts_work);

		else
@@ -228,9 +250,7 @@ static void tcindex_destroy_work(struct work_struct *work) 
					      struct tcindex_data,

					      rwork);



	kfree(p->perfect);

	kfree(p->h);

	kfree(p);

	tcindex_data_put(p);

}



static inline int
@@ -248,9 +268,11 @@ static const struct nla_policy tcindex_policy[TCA_TCINDEX_MAX + 1] = { 
};



static int tcindex_filter_result_init(struct tcindex_filter_result *r,

				      struct tcindex_data *p,

				      struct net *net)

{

	memset(r, 0, sizeof(*r));

	r->p = p;

	return tcf_exts_init(&r->exts, net, TCA_TCINDEX_ACT,

			     TCA_TCINDEX_POLICE);

}
@@ -290,6 +312,7 @@ static int tcindex_alloc_perfect_hash(struct net *net, struct tcindex_data *cp) 
				    TCA_TCINDEX_ACT, TCA_TCINDEX_POLICE);

		if (err < 0)

			goto errout;

		cp->perfect[i].p = cp;

	}



	return 0;
@@ -334,6 +357,7 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base, 
	cp->alloc_hash = p->alloc_hash;

	cp->fall_through = p->fall_through;

	cp->tp = tp;

	refcount_set(&cp->refcnt, 1); /* Paired with tcindex_destroy_work() */



	if (tb[TCA_TCINDEX_HASH])

		cp->hash = nla_get_u32(tb[TCA_TCINDEX_HASH]);
@@ -366,7 +390,7 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base, 
	}

	cp->h = p->h;



	err = tcindex_filter_result_init(&new_filter_result, net);

	err = tcindex_filter_result_init(&new_filter_result, cp, net);

	if (err < 0)

		goto errout_alloc;

	if (old_r)
@@ -434,7 +458,7 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base, 
			goto errout_alloc;

		f->key = handle;

		f->next = NULL;

		err = tcindex_filter_result_init(&f->result, net);

		err = tcindex_filter_result_init(&f->result, cp, net);

		if (err < 0) {

			kfree(f);

			goto errout_alloc;
@@ -447,7 +471,7 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base, 
	}



	if (old_r && old_r != r) {

		err = tcindex_filter_result_init(old_r, net);

		err = tcindex_filter_result_init(old_r, cp, net);

		if (err < 0) {

			kfree(f);

			goto errout_alloc;
@@ -571,6 +595,14 @@ static void tcindex_destroy(struct tcf_proto *tp, bool rtnl_held, 
		for (i = 0; i < p->hash; i++) {

			struct tcindex_filter_result *r = p->perfect + i;



			/* tcf_queue_work() does not guarantee the ordering we

			 * want, so we have to take this refcnt temporarily to

			 * ensure 'p' is freed after all tcindex_filter_result

			 * here. Imperfect hash does not need this, because it

			 * uses linked lists rather than an array.

			 */

			tcindex_data_get(p);



			tcf_unbind_filter(tp, &r->res);

			if (tcf_exts_get_net(&r->exts))

				tcf_queue_work(&r->rwork,

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