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>
---
Changes in v2:
- Removed a comment in sctp_init_sock.
- Added a CVE number.
net/sctp/socket.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index a710917c5ac7..b9b3d899a611 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1520,11 +1520,9 @@ static void sctp_close(struct sock *sk, long timeout)
/* 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.
@@ -1533,7 +1531,7 @@ static void sctp_close(struct sock *sk, long timeout)
sk_common_release(sk);
bh_unlock_sock(sk);
- spin_unlock_bh(&net->sctp.addr_wq_lock);
+ local_bh_enable();
sock_put(sk);
@@ -4993,9 +4991,6 @@ static int sctp_init_sock(struct sock *sk)
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,
@@ -5030,7 +5025,9 @@ static void sctp_destroy_sock(struct sock *sk)
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();
--
2.7.4
