Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 831de271 authored by Xin Long's avatar Xin Long Committed by Greg Kroah-Hartman
Browse files

sctp: use call_rcu to free endpoint 



[ Upstream commit 5ec7d18d1813a5bead0b495045606c93873aecbb ]

This patch is to delay the endpoint free by calling call_rcu() to fix
another use-after-free issue in sctp_sock_dump():

  BUG: KASAN: use-after-free in __lock_acquire+0x36d9/0x4c20
  Call Trace:
    __lock_acquire+0x36d9/0x4c20 kernel/locking/lockdep.c:3218
    lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3844
    __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
    _raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:168
    spin_lock_bh include/linux/spinlock.h:334 [inline]
    __lock_sock+0x203/0x350 net/core/sock.c:2253
    lock_sock_nested+0xfe/0x120 net/core/sock.c:2774
    lock_sock include/net/sock.h:1492 [inline]
    sctp_sock_dump+0x122/0xb20 net/sctp/diag.c:324
    sctp_for_each_transport+0x2b5/0x370 net/sctp/socket.c:5091
    sctp_diag_dump+0x3ac/0x660 net/sctp/diag.c:527
    __inet_diag_dump+0xa8/0x140 net/ipv4/inet_diag.c:1049
    inet_diag_dump+0x9b/0x110 net/ipv4/inet_diag.c:1065
    netlink_dump+0x606/0x1080 net/netlink/af_netlink.c:2244
    __netlink_dump_start+0x59a/0x7c0 net/netlink/af_netlink.c:2352
    netlink_dump_start include/linux/netlink.h:216 [inline]
    inet_diag_handler_cmd+0x2ce/0x3f0 net/ipv4/inet_diag.c:1170
    __sock_diag_cmd net/core/sock_diag.c:232 [inline]
    sock_diag_rcv_msg+0x31d/0x410 net/core/sock_diag.c:263
    netlink_rcv_skb+0x172/0x440 net/netlink/af_netlink.c:2477
    sock_diag_rcv+0x2a/0x40 net/core/sock_diag.c:274

This issue occurs when asoc is peeled off and the old sk is freed after
getting it by asoc->base.sk and before calling lock_sock(sk).

To prevent the sk free, as a holder of the sk, ep should be alive when
calling lock_sock(). This patch uses call_rcu() and moves sock_put and
ep free into sctp_endpoint_destroy_rcu(), so that it's safe to try to
hold the ep under rcu_read_lock in sctp_transport_traverse_process().

If sctp_endpoint_hold() returns true, it means this ep is still alive
and we have held it and can continue to dump it; If it returns false,
it means this ep is dead and can be freed after rcu_read_unlock, and
we should skip it.

In sctp_sock_dump(), after locking the sk, if this ep is different from
tsp->asoc->ep, it means during this dumping, this asoc was peeled off
before calling lock_sock(), and the sk should be skipped; If this ep is
the same with tsp->asoc->ep, it means no peeloff happens on this asoc,
and due to lock_sock, no peeloff will happen either until release_sock.

Note that delaying endpoint free won't delay the port release, as the
port release happens in sctp_endpoint_destroy() before calling call_rcu().
Also, freeing endpoint by call_rcu() makes it safe to access the sk by
asoc->base.sk in sctp_assocs_seq_show() and sctp_rcv().

Thanks Jones to bring this issue up.

v1->v2:
  - improve the changelog.
  - add kfree(ep) into sctp_endpoint_destroy_rcu(), as Jakub noticed.

Reported-by: default avatar <syzbot+9276d76e83e3bcde6c99@syzkaller.appspotmail.com>
Reported-by: default avatarLee Jones <lee.jones@linaro.org>
Fixes: d25adbeb ("sctp: fix an use-after-free issue in sctp_sock_dump")
Signed-off-by: default avatarXin Long <lucien.xin@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 3218d6bd

include/net/sctp/sctp.h

+3 −3
Original line number Diff line number Diff line
@@ -103,6 +103,7 @@ extern struct percpu_counter sctp_sockets_allocated; 
int sctp_asconf_mgmt(struct sctp_sock *, struct sctp_sockaddr_entry *);

struct sk_buff *sctp_skb_recv_datagram(struct sock *, int, int, int *);



typedef int (*sctp_callback_t)(struct sctp_endpoint *, struct sctp_transport *, void *);

void sctp_transport_walk_start(struct rhashtable_iter *iter);

void sctp_transport_walk_stop(struct rhashtable_iter *iter);

struct sctp_transport *sctp_transport_get_next(struct net *net,
@@ -113,8 +114,7 @@ int sctp_transport_lookup_process(int (*cb)(struct sctp_transport *, void *), 
				  struct net *net,

				  const union sctp_addr *laddr,

				  const union sctp_addr *paddr, void *p);

int sctp_for_each_transport(int (*cb)(struct sctp_transport *, void *),

			    int (*cb_done)(struct sctp_transport *, void *),

int sctp_transport_traverse_process(sctp_callback_t cb, sctp_callback_t cb_done,

				    struct net *net, int *pos, void *p);

int sctp_for_each_endpoint(int (*cb)(struct sctp_endpoint *, void *), void *p);

int sctp_get_sctp_info(struct sock *sk, struct sctp_association *asoc,

include/net/sctp/structs.h

+2 −1
Original line number Diff line number Diff line
@@ -1345,6 +1345,7 @@ struct sctp_endpoint { 


	u32 secid;

	u32 peer_secid;

	struct rcu_head rcu;

};



/* Recover the outter endpoint structure. */
@@ -1360,7 +1361,7 @@ static inline struct sctp_endpoint *sctp_ep(struct sctp_ep_common *base) 
struct sctp_endpoint *sctp_endpoint_new(struct sock *, gfp_t);

void sctp_endpoint_free(struct sctp_endpoint *);

void sctp_endpoint_put(struct sctp_endpoint *);

void sctp_endpoint_hold(struct sctp_endpoint *);

int sctp_endpoint_hold(struct sctp_endpoint *ep);

void sctp_endpoint_add_asoc(struct sctp_endpoint *, struct sctp_association *);

struct sctp_association *sctp_endpoint_lookup_assoc(

	const struct sctp_endpoint *ep,

net/sctp/diag.c

+6 −6
Original line number Diff line number Diff line
@@ -292,9 +292,8 @@ static int sctp_tsp_dump_one(struct sctp_transport *tsp, void *p) 
	return err;

}



static int sctp_sock_dump(struct sctp_transport *tsp, void *p)

static int sctp_sock_dump(struct sctp_endpoint *ep, struct sctp_transport *tsp, void *p)

{

	struct sctp_endpoint *ep = tsp->asoc->ep;

	struct sctp_comm_param *commp = p;

	struct sock *sk = ep->base.sk;

	struct sk_buff *skb = commp->skb;
@@ -304,6 +303,8 @@ static int sctp_sock_dump(struct sctp_transport *tsp, void *p) 
	int err = 0;



	lock_sock(sk);

	if (ep != tsp->asoc->ep)

		goto release;

	list_for_each_entry(assoc, &ep->asocs, asocs) {

		if (cb->args[4] < cb->args[1])

			goto next;
@@ -346,9 +347,8 @@ static int sctp_sock_dump(struct sctp_transport *tsp, void *p) 
	return err;

}



static int sctp_sock_filter(struct sctp_transport *tsp, void *p)

static int sctp_sock_filter(struct sctp_endpoint *ep, struct sctp_transport *tsp, void *p)

{

	struct sctp_endpoint *ep = tsp->asoc->ep;

	struct sctp_comm_param *commp = p;

	struct sock *sk = ep->base.sk;

	const struct inet_diag_req_v2 *r = commp->r;
@@ -506,7 +506,7 @@ static void sctp_diag_dump(struct sk_buff *skb, struct netlink_callback *cb, 
	if (!(idiag_states & ~(TCPF_LISTEN | TCPF_CLOSE)))

		goto done;



	sctp_for_each_transport(sctp_sock_filter, sctp_sock_dump,

	sctp_transport_traverse_process(sctp_sock_filter, sctp_sock_dump,

					net, &pos, &commp);

	cb->args[2] = pos;

net/sctp/endpointola.c

+15 −8
Original line number Diff line number Diff line
@@ -184,6 +184,18 @@ void sctp_endpoint_free(struct sctp_endpoint *ep) 
}



/* Final destructor for endpoint.  */

static void sctp_endpoint_destroy_rcu(struct rcu_head *head)

{

	struct sctp_endpoint *ep = container_of(head, struct sctp_endpoint, rcu);

	struct sock *sk = ep->base.sk;



	sctp_sk(sk)->ep = NULL;

	sock_put(sk);



	kfree(ep);

	SCTP_DBG_OBJCNT_DEC(ep);

}



static void sctp_endpoint_destroy(struct sctp_endpoint *ep)

{

	struct sock *sk;
@@ -213,18 +225,13 @@ static void sctp_endpoint_destroy(struct sctp_endpoint *ep) 
	if (sctp_sk(sk)->bind_hash)

		sctp_put_port(sk);



	sctp_sk(sk)->ep = NULL;

	/* Give up our hold on the sock */

	sock_put(sk);



	kfree(ep);

	SCTP_DBG_OBJCNT_DEC(ep);

	call_rcu(&ep->rcu, sctp_endpoint_destroy_rcu);

}



/* Hold a reference to an endpoint. */

void sctp_endpoint_hold(struct sctp_endpoint *ep)

int sctp_endpoint_hold(struct sctp_endpoint *ep)

{

	refcount_inc(&ep->base.refcnt);

	return refcount_inc_not_zero(&ep->base.refcnt);

}



/* Release a reference to an endpoint and clean up if there are

net/sctp/socket.c

+15 −8
Original line number Diff line number Diff line
@@ -5395,11 +5395,12 @@ int sctp_transport_lookup_process(int (*cb)(struct sctp_transport *, void *), 
}

EXPORT_SYMBOL_GPL(sctp_transport_lookup_process);



int sctp_for_each_transport(int (*cb)(struct sctp_transport *, void *),

			    int (*cb_done)(struct sctp_transport *, void *),

			    struct net *net, int *pos, void *p) {

int sctp_transport_traverse_process(sctp_callback_t cb, sctp_callback_t cb_done,

				    struct net *net, int *pos, void *p)

{

	struct rhashtable_iter hti;

	struct sctp_transport *tsp;

	struct sctp_endpoint *ep;

	int ret;



again:
@@ -5408,26 +5409,32 @@ int sctp_for_each_transport(int (*cb)(struct sctp_transport *, void *), 


	tsp = sctp_transport_get_idx(net, &hti, *pos + 1);

	for (; !IS_ERR_OR_NULL(tsp); tsp = sctp_transport_get_next(net, &hti)) {

		ret = cb(tsp, p);

		ep = tsp->asoc->ep;

		if (sctp_endpoint_hold(ep)) { /* asoc can be peeled off */

			ret = cb(ep, tsp, p);

			if (ret)

				break;

			sctp_endpoint_put(ep);

		}

		(*pos)++;

		sctp_transport_put(tsp);

	}

	sctp_transport_walk_stop(&hti);



	if (ret) {

		if (cb_done && !cb_done(tsp, p)) {

		if (cb_done && !cb_done(ep, tsp, p)) {

			(*pos)++;

			sctp_endpoint_put(ep);

			sctp_transport_put(tsp);

			goto again;

		}

		sctp_endpoint_put(ep);

		sctp_transport_put(tsp);

	}



	return ret;

}

EXPORT_SYMBOL_GPL(sctp_for_each_transport);

EXPORT_SYMBOL_GPL(sctp_transport_traverse_process);



/* 7.2.1 Association Status (SCTP_STATUS)