From 5ec7d18d1813a5bead0b495045606c93873aecbb Mon Sep 17 00:00:00 2001 From: Xin Long Date: Thu, 23 Dec 2021 13:04:30 -0500 Subject: sctp: use call_rcu to free endpoint 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: syzbot+9276d76e83e3bcde6c99@syzkaller.appspotmail.com Reported-by: Lee Jones Fixes: d25adbeb0cdb ("sctp: fix an use-after-free issue in sctp_sock_dump") Signed-off-by: Xin Long Signed-off-by: David S. Miller --- net/sctp/diag.c | 12 ++++++------ net/sctp/endpointola.c | 23 +++++++++++++++-------- net/sctp/socket.c | 23 +++++++++++++++-------- 3 files changed, 36 insertions(+), 22 deletions(-) (limited to 'net') diff --git a/net/sctp/diag.c b/net/sctp/diag.c index 760b367644c1..a7d623171501 100644 --- a/net/sctp/diag.c +++ b/net/sctp/diag.c @@ -290,9 +290,8 @@ out: 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; @@ -302,6 +301,8 @@ 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; @@ -344,9 +345,8 @@ release: 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; @@ -505,8 +505,8 @@ skip: if (!(idiag_states & ~(TCPF_LISTEN | TCPF_CLOSE))) goto done; - sctp_for_each_transport(sctp_sock_filter, sctp_sock_dump, - net, &pos, &commp); + sctp_transport_traverse_process(sctp_sock_filter, sctp_sock_dump, + net, &pos, &commp); cb->args[2] = pos; done: diff --git a/net/sctp/endpointola.c b/net/sctp/endpointola.c index 48c9c2c7602f..efffde7f2328 100644 --- a/net/sctp/endpointola.c +++ b/net/sctp/endpointola.c @@ -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 diff --git a/net/sctp/socket.c b/net/sctp/socket.c index 33391254fa82..ad5028a07b18 100644 --- a/net/sctp/socket.c +++ b/net/sctp/socket.c @@ -5338,11 +5338,12 @@ 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: @@ -5351,26 +5352,32 @@ again: 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); - if (ret) - break; + 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) -- cgit v1.2.3