This is a note to let you know that I've just added the patch titled Revert "net/sctp: fix race condition in sctp_destroy_sock" to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: revert-net-sctp-fix-race-condition-in-sctp_destroy_sock.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 01bfe5e8e428b475982a98a46cca5755726f3f7f Mon Sep 17 00:00:00 2001 From: Xin Long <lucien.xin@xxxxxxxxx> Date: Mon, 3 May 2021 05:11:41 +0800 Subject: Revert "net/sctp: fix race condition in sctp_destroy_sock" From: Xin Long <lucien.xin@xxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/sctp/socket.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) --- a/net/sctp/socket.c +++ b/net/sctp/socket.c @@ -1569,9 +1569,11 @@ 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. @@ -1580,7 +1582,7 @@ 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); @@ -4774,6 +4776,9 @@ 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, @@ -4808,9 +4813,7 @@ 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(); Patches currently in stable-queue which might be from lucien.xin@xxxxxxxxx are queue-4.19/sctp-delay-auto_asconf-init-until-binding-the-first-addr.patch queue-4.19/revert-net-sctp-fix-race-condition-in-sctp_destroy_sock.patch