[PATCH 4.9 01/37] net/sctp: fix race condition in sctp_destroy_sock

Greg Kroah-Hartman
2021-04-26T07:32:26Z

From: Or Cohen <orcohen@paloaltonetworks.com>

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

--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1582,11 +1582,9 @@ 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.
@@ -1595,7 +1593,7 @@ 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);

@@ -4262,9 +4260,6 @@ 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,
@@ -4299,7 +4294,9 @@ 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();