[PATCH 5.4 09/73] net/sctp: fix race condition in sctp_destroy_sock

[Greg Kroah-Hartman]

From: Or Cohen <orcohen@xxxxxxxxxxxxxxxxxxxx>

commit b166a20b07382b8bc1dcee2a448715c9c2c81b5b upstream.

If sctp_destroy_sock is called without sock_net(sk)->sctp.addr_wq_lock
held and sp->do_auto_asconf is true, then an element is removed
from the auto_asconf_splist without any proper locking.

This can happen in the following functions:
1. In sctp_accept, if sctp_sock_migrate fails.
2. In inet_create or inet6_create, if there is a bpf program
   attached to BPF_CGROUP_INET_SOCK_CREATE which denies
   creation of the sctp socket.

The bug is fixed by acquiring addr_wq_lock in sctp_destroy_sock
instead of sctp_close.

This addresses CVE-2021-23133.

Reported-by: Or Cohen <orcohen@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Xin Long <lucien.xin@xxxxxxxxx>
Fixes: 610236587600 ("bpf: Add new cgroup attach type to enable sock modifications")
Signed-off-by: Or Cohen <orcohen@xxxxxxxxxxxxxxxxxxxx>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@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, 5 insertions(+), 8 deletions(-)

--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1539,11 +1539,9 @@ 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.
 	 */
-	spin_lock_bh(&net->sctp.addr_wq_lock);
-	bh_lock_sock_nested(sk);
+	local_bh_disable();
+	bh_lock_sock(sk);
 
 	/* Hold the sock, since sk_common_release() will put sock_put()
 	 * and we have just a little more cleanup.
@@ -1552,7 +1550,7 @@ static void sctp_close(struct sock *sk,
 	sk_common_release(sk);
 
 	bh_unlock_sock(sk);
-	spin_unlock_bh(&net->sctp.addr_wq_lock);
+	local_bh_enable();
 
 	sock_put(sk);
 
@@ -5115,9 +5113,6 @@ 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,
@@ -5152,7 +5147,9 @@ 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();