sockmap.c

/* Copyright (c) 2017 Covalent IO, Inc. http://covalent.io
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 */

/* A BPF sock_map is used to store sock objects. This is primarly used
 * for doing socket redirect with BPF helper routines.
 *
 * A sock map may have two BPF programs attached to it, a program used
 * to parse packets and a program to provide a verdict and redirect
 * decision on the packet. If no BPF parse program is provided it is
 * assumed that every skb is a "message" (skb->len). Otherwise the
 * parse program is attached to strparser and used to build messages
 * that may span multiple skbs. The verdict program will either select
 * a socket to send/receive the skb on or provide the drop code indicating
 * the skb should be dropped. More actions may be added later as needed.
 * The default program will drop packets.
 *
 * For reference this program is similar to devmap used in XDP context
 * reviewing these together may be useful. For an example please review
 * ./samples/bpf/sockmap/.
 */
#include <linux/bpf.h>
#include <net/sock.h>
#include <linux/filter.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/kernel.h>
#include <linux/net.h>
#include <linux/skbuff.h>
#include <linux/workqueue.h>
#include <linux/list.h>
#include <net/strparser.h>

struct bpf_stab {
	struct bpf_map map;
	struct sock **sock_map;
	struct bpf_prog *bpf_parse;
	struct bpf_prog *bpf_verdict;
	refcount_t refcnt;
};

enum smap_psock_state {
	SMAP_TX_RUNNING,
};

struct smap_psock {
	struct rcu_head	rcu;

	/* datapath variables */
	struct sk_buff_head rxqueue;
	bool strp_enabled;

	/* datapath error path cache across tx work invocations */
	int save_rem;
	int save_off;
	struct sk_buff *save_skb;

	struct strparser strp;
	struct bpf_prog *bpf_parse;
	struct bpf_prog *bpf_verdict;
	struct bpf_stab *stab;

	/* Back reference used when sock callback trigger sockmap operations */
	int key;
	struct sock *sock;
	unsigned long state;

	struct work_struct tx_work;
	struct work_struct gc_work;

	void (*save_data_ready)(struct sock *sk);
	void (*save_write_space)(struct sock *sk);
	void (*save_state_change)(struct sock *sk);
};

static inline struct smap_psock *smap_psock_sk(const struct sock *sk)
{
	return (struct smap_psock *)rcu_dereference_sk_user_data(sk);
}

static int smap_verdict_func(struct smap_psock *psock, struct sk_buff *skb)
{
	struct bpf_prog *prog = READ_ONCE(psock->bpf_verdict);
	int rc;

	if (unlikely(!prog))
		return SK_DROP;

	skb_orphan(skb);
	skb->sk = psock->sock;
	bpf_compute_data_end(skb);
	rc = (*prog->bpf_func)(skb, prog->insnsi);
	skb->sk = NULL;

	return rc;
}

static void smap_do_verdict(struct smap_psock *psock, struct sk_buff *skb)
{
	struct sock *sock;
	int rc;

	/* Because we use per cpu values to feed input from sock redirect
	 * in BPF program to do_sk_redirect_map() call we need to ensure we
	 * are not preempted. RCU read lock is not sufficient in this case
	 * with CONFIG_PREEMPT_RCU enabled so we must be explicit here.
	 */
	preempt_disable();
	rc = smap_verdict_func(psock, skb);
	switch (rc) {
	case SK_REDIRECT:
		sock = do_sk_redirect_map();
		preempt_enable();
		if (likely(sock)) {
			struct smap_psock *peer = smap_psock_sk(sock);

			if (likely(peer &&
				   test_bit(SMAP_TX_RUNNING, &peer->state) &&
				   sk_stream_memory_free(peer->sock))) {
				peer->sock->sk_wmem_queued += skb->truesize;
				sk_mem_charge(peer->sock, skb->truesize);
				skb_queue_tail(&peer->rxqueue, skb);
				schedule_work(&peer->tx_work);
				break;
			}
		}
	/* Fall through and free skb otherwise */
	case SK_DROP:
	default:
		if (rc != SK_REDIRECT)
			preempt_enable();
		kfree_skb(skb);
	}
}

static void smap_report_sk_error(struct smap_psock *psock, int err)
{
	struct sock *sk = psock->sock;

	sk->sk_err = err;
	sk->sk_error_report(sk);
}

static void smap_release_sock(struct sock *sock);

/* Called with lock_sock(sk) held */
static void smap_state_change(struct sock *sk)
{
	struct smap_psock *psock;
	struct sock *osk;

	rcu_read_lock();

	/* Allowing transitions into an established syn_recv states allows
	 * for early binding sockets to a smap object before the connection
	 * is established.
	 */
	switch (sk->sk_state) {
	case TCP_SYN_RECV:
	case TCP_ESTABLISHED:
		break;
	case TCP_CLOSE_WAIT:
	case TCP_CLOSING:
	case TCP_LAST_ACK:
	case TCP_FIN_WAIT1:
	case TCP_FIN_WAIT2:
	case TCP_LISTEN:
		break;
	case TCP_CLOSE:
		/* Only release if the map entry is in fact the sock in
		 * question. There is a case where the operator deletes
		 * the sock from the map, but the TCP sock is closed before
		 * the psock is detached. Use cmpxchg to verify correct
		 * sock is removed.
		 */
		psock = smap_psock_sk(sk);
		if (unlikely(!psock))
			break;
		osk = cmpxchg(&psock->stab->sock_map[psock->key], sk, NULL);
		if (osk == sk)
			smap_release_sock(sk);
		break;
	default:
		psock = smap_psock_sk(sk);
		if (unlikely(!psock))
			break;
		smap_report_sk_error(psock, EPIPE);
		break;
	}
	rcu_read_unlock();
}

static void smap_read_sock_strparser(struct strparser *strp,
				     struct sk_buff *skb)
{
	struct smap_psock *psock;

	rcu_read_lock();
	psock = container_of(strp, struct smap_psock, strp);
	smap_do_verdict(psock, skb);
	rcu_read_unlock();
}

/* Called with lock held on socket */
static void smap_data_ready(struct sock *sk)
{
	struct smap_psock *psock;

	write_lock_bh(&sk->sk_callback_lock);
	psock = smap_psock_sk(sk);
	if (likely(psock))
		strp_data_ready(&psock->strp);
	write_unlock_bh(&sk->sk_callback_lock);
}

static void smap_tx_work(struct work_struct *w)
{
	struct smap_psock *psock;
	struct sk_buff *skb;
	int rem, off, n;

	psock = container_of(w, struct smap_psock, tx_work);

	/* lock sock to avoid losing sk_socket at some point during loop */
	lock_sock(psock->sock);
	if (psock->save_skb) {
		skb = psock->save_skb;
		rem = psock->save_rem;
		off = psock->save_off;
		psock->save_skb = NULL;
		goto start;
	}

	while ((skb = skb_dequeue(&psock->rxqueue))) {
		rem = skb->len;
		off = 0;
start:
		do {
			if (likely(psock->sock->sk_socket))
				n = skb_send_sock_locked(psock->sock,
							 skb, off, rem);
			else
				n = -EINVAL;
			if (n <= 0) {
				if (n == -EAGAIN) {
					/* Retry when space is available */
					psock->save_skb = skb;
					psock->save_rem = rem;
					psock->save_off = off;
					goto out;
				}
				/* Hard errors break pipe and stop xmit */
				smap_report_sk_error(psock, n ? -n : EPIPE);
				clear_bit(SMAP_TX_RUNNING, &psock->state);
				sk_mem_uncharge(psock->sock, skb->truesize);
				psock->sock->sk_wmem_queued -= skb->truesize;
				kfree_skb(skb);
				goto out;
			}
			rem -= n;
			off += n;
		} while (rem);
		sk_mem_uncharge(psock->sock, skb->truesize);
		psock->sock->sk_wmem_queued -= skb->truesize;
		kfree_skb(skb);
	}
out:
	release_sock(psock->sock);
}

static void smap_write_space(struct sock *sk)
{
	struct smap_psock *psock;

	rcu_read_lock();
	psock = smap_psock_sk(sk);
	if (likely(psock && test_bit(SMAP_TX_RUNNING, &psock->state)))
		schedule_work(&psock->tx_work);
	rcu_read_unlock();
}

static void smap_stop_sock(struct smap_psock *psock, struct sock *sk)
{
	write_lock_bh(&sk->sk_callback_lock);
	if (!psock->strp_enabled)
		goto out;
	sk->sk_data_ready = psock->save_data_ready;
	sk->sk_write_space = psock->save_write_space;
	sk->sk_state_change = psock->save_state_change;
	psock->save_data_ready = NULL;
	psock->save_write_space = NULL;
	psock->save_state_change = NULL;
	strp_stop(&psock->strp);
	psock->strp_enabled = false;
out:
	write_unlock_bh(&sk->sk_callback_lock);
}

static void smap_destroy_psock(struct rcu_head *rcu)
{
	struct smap_psock *psock = container_of(rcu,
						  struct smap_psock, rcu);

	/* Now that a grace period has passed there is no longer
	 * any reference to this sock in the sockmap so we can
	 * destroy the psock, strparser, and bpf programs. But,
	 * because we use workqueue sync operations we can not
	 * do it in rcu context
	 */
	schedule_work(&psock->gc_work);
}

static void smap_release_sock(struct sock *sock)
{
	struct smap_psock *psock = smap_psock_sk(sock);

	smap_stop_sock(psock, sock);
	clear_bit(SMAP_TX_RUNNING, &psock->state);
	rcu_assign_sk_user_data(sock, NULL);
	call_rcu_sched(&psock->rcu, smap_destroy_psock);
}

static int smap_parse_func_strparser(struct strparser *strp,
				       struct sk_buff *skb)
{
	struct smap_psock *psock;
	struct bpf_prog *prog;
	int rc;

	rcu_read_lock();
	psock = container_of(strp, struct smap_psock, strp);
	prog = READ_ONCE(psock->bpf_parse);

	if (unlikely(!prog)) {
		rcu_read_unlock();
		return skb->len;
	}

	/* Attach socket for bpf program to use if needed we can do this
	 * because strparser clones the skb before handing it to a upper
	 * layer, meaning skb_orphan has been called. We NULL sk on the
	 * way out to ensure we don't trigger a BUG_ON in skb/sk operations
	 * later and because we are not charging the memory of this skb to
	 * any socket yet.
	 */
	skb->sk = psock->sock;
	bpf_compute_data_end(skb);
	rc = (*prog->bpf_func)(skb, prog->insnsi);
	skb->sk = NULL;
	rcu_read_unlock();
	return rc;
}


static int smap_read_sock_done(struct strparser *strp, int err)
{
	return err;
}

static int smap_init_sock(struct smap_psock *psock,
			  struct sock *sk)
{
	struct strp_callbacks cb;

	memset(&cb, 0, sizeof(cb));
	cb.rcv_msg = smap_read_sock_strparser;
	cb.parse_msg = smap_parse_func_strparser;
	cb.read_sock_done = smap_read_sock_done;
	return strp_init(&psock->strp, sk, &cb);
}

static void smap_init_progs(struct smap_psock *psock,
			    struct bpf_stab *stab,
			    struct bpf_prog *verdict,
			    struct bpf_prog *parse)
{
	struct bpf_prog *orig_parse, *orig_verdict;

	orig_parse = xchg(&psock->bpf_parse, parse);
	orig_verdict = xchg(&psock->bpf_verdict, verdict);

	if (orig_verdict)
		bpf_prog_put(orig_verdict);
	if (orig_parse)
		bpf_prog_put(orig_parse);
}

static void smap_start_sock(struct smap_psock *psock, struct sock *sk)
{
	if (sk->sk_data_ready == smap_data_ready)
		return;
	psock->save_data_ready = sk->sk_data_ready;
	psock->save_write_space = sk->sk_write_space;
	psock->save_state_change = sk->sk_state_change;
	sk->sk_data_ready = smap_data_ready;
	sk->sk_write_space = smap_write_space;
	sk->sk_state_change = smap_state_change;
	psock->strp_enabled = true;
}

static void sock_map_remove_complete(struct bpf_stab *stab)
{
	bpf_map_area_free(stab->sock_map);
	kfree(stab);
}

static void smap_gc_work(struct work_struct *w)
{
	struct smap_psock *psock;

	psock = container_of(w, struct smap_psock, gc_work);

	/* no callback lock needed because we already detached sockmap ops */
	if (psock->strp_enabled)
		strp_done(&psock->strp);

	cancel_work_sync(&psock->tx_work);
	__skb_queue_purge(&psock->rxqueue);

	/* At this point all strparser and xmit work must be complete */
	if (psock->bpf_parse)
		bpf_prog_put(psock->bpf_parse);
	if (psock->bpf_verdict)
		bpf_prog_put(psock->bpf_verdict);

	if (refcount_dec_and_test(&psock->stab->refcnt))
		sock_map_remove_complete(psock->stab);

	sock_put(psock->sock);
	kfree(psock);
}

static struct smap_psock *smap_init_psock(struct sock *sock,
					  struct bpf_stab *stab)
{
	struct smap_psock *psock;

	psock = kzalloc(sizeof(struct smap_psock), GFP_ATOMIC | __GFP_NOWARN);
	if (!psock)
		return ERR_PTR(-ENOMEM);

	psock->sock = sock;
	skb_queue_head_init(&psock->rxqueue);
	INIT_WORK(&psock->tx_work, smap_tx_work);
	INIT_WORK(&psock->gc_work, smap_gc_work);

	rcu_assign_sk_user_data(sock, psock);
	sock_hold(sock);
	return psock;
}

static struct bpf_map *sock_map_alloc(union bpf_attr *attr)
{
	struct bpf_stab *stab;
	int err = -EINVAL;
	u64 cost;

	/* check sanity of attributes */
	if (attr->max_entries == 0 || attr->key_size != 4 ||
	    attr->value_size != 4 || attr->map_flags)
		return ERR_PTR(-EINVAL);

	if (attr->value_size > KMALLOC_MAX_SIZE)
		return ERR_PTR(-E2BIG);

	stab = kzalloc(sizeof(*stab), GFP_USER);
	if (!stab)
		return ERR_PTR(-ENOMEM);

	/* mandatory map attributes */
	stab->map.map_type = attr->map_type;
	stab->map.key_size = attr->key_size;
	stab->map.value_size = attr->value_size;
	stab->map.max_entries = attr->max_entries;
	stab->map.map_flags = attr->map_flags;

	/* make sure page count doesn't overflow */
	cost = (u64) stab->map.max_entries * sizeof(struct sock *);
	if (cost >= U32_MAX - PAGE_SIZE)
		goto free_stab;

	stab->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;

	/* if map size is larger than memlock limit, reject it early */
	err = bpf_map_precharge_memlock(stab->map.pages);
	if (err)
		goto free_stab;

	stab->sock_map = bpf_map_area_alloc(stab->map.max_entries *
					    sizeof(struct sock *));
	if (!stab->sock_map)
		goto free_stab;

	refcount_set(&stab->refcnt, 1);
	return &stab->map;
free_stab:
	kfree(stab);
	return ERR_PTR(err);
}

static void sock_map_free(struct bpf_map *map)
{
	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
	int i;

	synchronize_rcu();

	/* At this point no update, lookup or delete operations can happen.
	 * However, be aware we can still get a socket state event updates,
	 * and data ready callabacks that reference the psock from sk_user_data
	 * Also psock worker threads are still in-flight. So smap_release_sock
	 * will only free the psock after cancel_sync on the worker threads
	 * and a grace period expire to ensure psock is really safe to remove.
	 */
	rcu_read_lock();
	for (i = 0; i < stab->map.max_entries; i++) {
		struct sock *sock;

		sock = xchg(&stab->sock_map[i], NULL);
		if (!sock)
			continue;

		smap_release_sock(sock);
	}
	rcu_read_unlock();

	if (stab->bpf_verdict)
		bpf_prog_put(stab->bpf_verdict);
	if (stab->bpf_parse)
		bpf_prog_put(stab->bpf_parse);

	if (refcount_dec_and_test(&stab->refcnt))
		sock_map_remove_complete(stab);
}

static int sock_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
{
	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
	u32 i = key ? *(u32 *)key : U32_MAX;
	u32 *next = (u32 *)next_key;

	if (i >= stab->map.max_entries) {
		*next = 0;
		return 0;
	}

	if (i == stab->map.max_entries - 1)
		return -ENOENT;

	*next = i + 1;
	return 0;
}

struct sock  *__sock_map_lookup_elem(struct bpf_map *map, u32 key)
{
	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);

	if (key >= map->max_entries)
		return NULL;

	return READ_ONCE(stab->sock_map[key]);
}

static int sock_map_delete_elem(struct bpf_map *map, void *key)
{
	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
	int k = *(u32 *)key;
	struct sock *sock;

	if (k >= map->max_entries)
		return -EINVAL;

	sock = xchg(&stab->sock_map[k], NULL);
	if (!sock)
		return -EINVAL;

	smap_release_sock(sock);
	return 0;
}

/* Locking notes: Concurrent updates, deletes, and lookups are allowed and are
 * done inside rcu critical sections. This ensures on updates that the psock
 * will not be released via smap_release_sock() until concurrent updates/deletes
 * complete. All operations operate on sock_map using cmpxchg and xchg
 * operations to ensure we do not get stale references. Any reads into the
 * map must be done with READ_ONCE() because of this.
 *
 * A psock is destroyed via call_rcu and after any worker threads are cancelled
 * and syncd so we are certain all references from the update/lookup/delete
 * operations as well as references in the data path are no longer in use.
 *
 * A psock object holds a refcnt on the sockmap it is attached to and this is
 * not decremented until after a RCU grace period and garbage collection occurs.
 * This ensures the map is not free'd until psocks linked to it are removed. The
 * map link is used when the independent sock events trigger map deletion.
 *
 * Psocks may only participate in one sockmap at a time. Users that try to
 * join a single sock to multiple maps will get an error.
 *
 * Last, but not least, it is possible the socket is closed while running
 * an update on an existing psock. This will release the psock, but again
 * not until the update has completed due to rcu grace period rules.
 */
static int sock_map_ctx_update_elem(struct bpf_sock_ops_kern *skops,
				    struct bpf_map *map,
				    void *key, u64 flags, u64 map_flags)
{
	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
	struct bpf_prog *verdict, *parse;
	struct smap_psock *psock = NULL;
	struct sock *old_sock, *sock;
	u32 i = *(u32 *)key;
	bool update = false;
	int err = 0;

	if (unlikely(flags > BPF_EXIST))
		return -EINVAL;

	if (unlikely(i >= stab->map.max_entries))
		return -E2BIG;

	if (unlikely(map_flags > BPF_SOCKMAP_STRPARSER))
		return -EINVAL;

	verdict = parse = NULL;
	sock = READ_ONCE(stab->sock_map[i]);

	if (flags == BPF_EXIST || flags == BPF_ANY) {
		if (!sock && flags == BPF_EXIST) {
			return -ENOENT;
		} else if (sock && sock != skops->sk) {
			return -EINVAL;
		} else if (sock) {
			psock = smap_psock_sk(sock);
			if (unlikely(!psock))
				return -EBUSY;
			update = true;
		}
	} else if (sock && BPF_NOEXIST) {
		return -EEXIST;
	}

	/* reserve BPF programs early so can abort easily on failures */
	if (map_flags & BPF_SOCKMAP_STRPARSER) {
		verdict = READ_ONCE(stab->bpf_verdict);
		parse = READ_ONCE(stab->bpf_parse);

		if (!verdict || !parse)
			return -ENOENT;

		/* bpf prog refcnt may be zero if a concurrent attach operation
		 * removes the program after the above READ_ONCE() but before
		 * we increment the refcnt. If this is the case abort with an
		 * error.
		 */
		verdict = bpf_prog_inc_not_zero(stab->bpf_verdict);
		if (IS_ERR(verdict))
			return PTR_ERR(verdict);

		parse = bpf_prog_inc_not_zero(stab->bpf_parse);
		if (IS_ERR(parse)) {
			bpf_prog_put(verdict);
			return PTR_ERR(parse);
		}
	}

	if (!psock) {
		sock = skops->sk;
		if (rcu_dereference_sk_user_data(sock))
			return -EEXIST;
		psock = smap_init_psock(sock, stab);
		if (IS_ERR(psock)) {
			if (verdict)
				bpf_prog_put(verdict);
			if (parse)
				bpf_prog_put(parse);
			return PTR_ERR(psock);
		}
		psock->key = i;
		psock->stab = stab;
		refcount_inc(&stab->refcnt);
		set_bit(SMAP_TX_RUNNING, &psock->state);
	}

	if (map_flags & BPF_SOCKMAP_STRPARSER) {
		write_lock_bh(&sock->sk_callback_lock);
		if (psock->strp_enabled)
			goto start_done;
		err = smap_init_sock(psock, sock);
		if (err)
			goto out;
		smap_init_progs(psock, stab, verdict, parse);
		smap_start_sock(psock, sock);
start_done:
		write_unlock_bh(&sock->sk_callback_lock);
	} else if (update) {
		smap_stop_sock(psock, sock);
	}

	if (!update) {
		old_sock = xchg(&stab->sock_map[i], skops->sk);
		if (old_sock)
			smap_release_sock(old_sock);
	}

	return 0;
out:
	write_unlock_bh(&sock->sk_callback_lock);
	if (!update)
		smap_release_sock(sock);
	return err;
}

static int sock_map_attach_prog(struct bpf_map *map,
				struct bpf_prog *parse,
				struct bpf_prog *verdict)
{
	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
	struct bpf_prog *_parse, *_verdict;

	_parse = xchg(&stab->bpf_parse, parse);
	_verdict = xchg(&stab->bpf_verdict, verdict);

	if (_parse)
		bpf_prog_put(_parse);
	if (_verdict)
		bpf_prog_put(_verdict);

	return 0;
}

static void *sock_map_lookup(struct bpf_map *map, void *key)
{
	return NULL;
}

static int sock_map_update_elem(struct bpf_map *map,
				void *key, void *value, u64 flags)
{
	struct bpf_sock_ops_kern skops;
	u32 fd = *(u32 *)value;
	struct socket *socket;
	int err;

	socket = sockfd_lookup(fd, &err);
	if (!socket)
		return err;

	skops.sk = socket->sk;
	if (!skops.sk) {
		fput(socket->file);
		return -EINVAL;
	}

	err = sock_map_ctx_update_elem(&skops, map, key,
				       flags, BPF_SOCKMAP_STRPARSER);
	fput(socket->file);
	return err;
}

const struct bpf_map_ops sock_map_ops = {
	.map_alloc = sock_map_alloc,
	.map_free = sock_map_free,
	.map_lookup_elem = sock_map_lookup,
	.map_get_next_key = sock_map_get_next_key,
	.map_update_elem = sock_map_update_elem,
	.map_delete_elem = sock_map_delete_elem,
	.map_attach = sock_map_attach_prog,
};

BPF_CALL_5(bpf_sock_map_update, struct bpf_sock_ops_kern *, bpf_sock,
	   struct bpf_map *, map, void *, key, u64, flags, u64, map_flags)
{
	WARN_ON_ONCE(!rcu_read_lock_held());
	return sock_map_ctx_update_elem(bpf_sock, map, key, flags, map_flags);
}

const struct bpf_func_proto bpf_sock_map_update_proto = {
	.func		= bpf_sock_map_update,
	.gpl_only	= false,
	.pkt_access	= true,
	.ret_type	= RET_INTEGER,
	.arg1_type	= ARG_PTR_TO_CTX,
	.arg2_type	= ARG_CONST_MAP_PTR,
	.arg3_type	= ARG_PTR_TO_MAP_KEY,
	.arg4_type	= ARG_ANYTHING,
	.arg5_type	= ARG_ANYTHING,
};