--- /dev/null
+From 5ec7d18d1813a5bead0b495045606c93873aecbb Mon Sep 17 00:00:00 2001
+From: Xin Long <lucien.xin@gmail.com>
+Date: Thu, 23 Dec 2021 13:04:30 -0500
+Subject: sctp: use call_rcu to free endpoint
+
+From: Xin Long <lucien.xin@gmail.com>
+
+commit 5ec7d18d1813a5bead0b495045606c93873aecbb upstream.
+
+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 <lee.jones@linaro.org>
+Fixes: d25adbeb0cdb ("sctp: fix an use-after-free issue in sctp_sock_dump")
+Signed-off-by: Xin Long <lucien.xin@gmail.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ include/net/sctp/sctp.h | 6 +++---
+ include/net/sctp/structs.h | 3 ++-
+ net/sctp/endpointola.c | 23 +++++++++++++++--------
+ net/sctp/sctp_diag.c | 12 ++++++------
+ net/sctp/socket.c | 23 +++++++++++++++--------
+ 5 files changed, 41 insertions(+), 26 deletions(-)
+
+--- a/include/net/sctp/sctp.h
++++ b/include/net/sctp/sctp.h
+@@ -118,6 +118,7 @@ extern struct percpu_counter sctp_socket
+ 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 *);
+ int 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,
+@@ -128,9 +129,8 @@ int sctp_transport_lookup_process(int (*
+ 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 *),
+- 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);
+ 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,
+ struct sctp_info *info);
+--- a/include/net/sctp/structs.h
++++ b/include/net/sctp/structs.h
+@@ -1272,6 +1272,7 @@ struct sctp_endpoint {
+ reconf_enable:1;
+
+ __u8 strreset_enable;
++ struct rcu_head rcu;
+ };
+
+ /* Recover the outter endpoint structure. */
+@@ -1287,7 +1288,7 @@ static inline struct sctp_endpoint *sctp
+ 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,
+--- a/net/sctp/endpointola.c
++++ b/net/sctp/endpointola.c
+@@ -242,6 +242,18 @@ void sctp_endpoint_free(struct sctp_endp
+ }
+
+ /* 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;
+@@ -275,18 +287,13 @@ static void sctp_endpoint_destroy(struct
+ 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
+--- a/net/sctp/sctp_diag.c
++++ b/net/sctp/sctp_diag.c
+@@ -276,9 +276,8 @@ 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;
+@@ -288,6 +287,8 @@ static int sctp_sock_dump(struct sctp_tr
+ 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;
+@@ -330,9 +331,8 @@ 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;
+@@ -490,8 +490,8 @@ 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:
+--- a/net/sctp/socket.c
++++ b/net/sctp/socket.c
+@@ -4738,11 +4738,12 @@ int sctp_transport_lookup_process(int (*
+ }
+ 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:
+@@ -4752,26 +4753,32 @@ 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)
+
projects / thirdparty / kernel / stable-queue.git / commitdiff
