[PATCH 4.9 166/240] Revert "net/sctp: fix race condition in sctp_destroy_sock"

Greg Kroah-Hartman
2021-05-20T11:19:26Z

From: Xin Long <lucien.xin@gmail.com>

commit 01bfe5e8e428b475982a98a46cca5755726f3f7f upstream.

This reverts commit b166a20b07382b8bc1dcee2a448715c9c2c81b5b.

This one has to be reverted as it introduced a dead lock, as
syzbot reported:

CPU0 CPU1
---- ----
lock(&net->sctp.addr_wq_lock);
lock(slock-AF_INET6);
lock(&net->sctp.addr_wq_lock);
lock(slock-AF_INET6);

CPU0 is the thread of sctp_addr_wq_timeout_handler(), and CPU1
is that of sctp_close().

The original issue this commit fixed will be fixed in the next
patch.

Reported-by: syzbot+959223586843e69a2674@syzkaller.appspotmail.com
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>
---
net/sctp/socket.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1582,9 +1582,11 @@ static void sctp_close(struct sock *sk,

/* Supposedly, no process has access to the socket, but
* the net layers still may.
+ * Also, sctp_destroy_sock() needs to be called with addr_wq_lock
+ * held and that should be grabbed before socket lock.
*/
- local_bh_disable();
- bh_lock_sock(sk);
+ spin_lock_bh(&net->sctp.addr_wq_lock);
+ bh_lock_sock_nested(sk);

/* Hold the sock, since sk_common_release() will put sock_put()
* and we have just a little more cleanup.
@@ -1593,7 +1595,7 @@ static void sctp_close(struct sock *sk,
sk_common_release(sk);

bh_unlock_sock(sk);
- local_bh_enable();
+ spin_unlock_bh(&net->sctp.addr_wq_lock);

sock_put(sk);

@@ -4260,6 +4262,9 @@ static int sctp_init_sock(struct sock *s
sk_sockets_allocated_inc(sk);
sock_prot_inuse_add(net, sk->sk_prot, 1);

+ /* Nothing can fail after this block, otherwise
+ * sctp_destroy_sock() will be called without addr_wq_lock held
+ */
if (net->sctp.default_auto_asconf) {
spin_lock(&sock_net(sk)->sctp.addr_wq_lock);
list_add_tail(&sp->auto_asconf_list,
@@ -4294,9 +4299,7 @@ static void sctp_destroy_sock(struct soc

if (sp->do_auto_asconf) {
sp->do_auto_asconf = 0;
- spin_lock_bh(&sock_net(sk)->sctp.addr_wq_lock);
list_del(&sp->auto_asconf_list);
- spin_unlock_bh(&sock_net(sk)->sctp.addr_wq_lock);
}
sctp_endpoint_free(sp->ep);
local_bh_disable();