[PATCH 5.11 601/601] sctp: delay auto_asconf init until binding the first addr

Greg Kroah-Hartman
2021-05-12T18:06:05Z

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

commit 34e5b01186858b36c4d7c87e1a025071e8e2401f upstream.

As Or Cohen described:

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.

This patch is to fix it by moving the auto_asconf init out of
sctp_init_sock(), by which inet_create()/inet6_create() won't
need to operate it in sctp_destroy_sock() when calling
sk_common_release().

It also makes more sense to do auto_asconf init while binding the
first addr, as auto_asconf actually requires an ANY addr bind,
see it in sctp_addr_wq_timeout_handler().

This addresses CVE-2021-23133.

Fixes: 610236587600 ("bpf: Add new cgroup attach type to enable sock modifications")
Reported-by: Or Cohen <orcohen@paloaltonetworks.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 | 31 +++++++++++++++++--------------
1 file changed, 17 insertions(+), 14 deletions(-)

--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -357,6 +357,18 @@ static struct sctp_af *sctp_sockaddr_af(
return af;
}

+static void sctp_auto_asconf_init(struct sctp_sock *sp)
+{
+ struct net *net = sock_net(&sp->inet.sk);
+
+ if (net->sctp.default_auto_asconf) {
+ spin_lock(&net->sctp.addr_wq_lock);
+ list_add_tail(&sp->auto_asconf_list, &net->sctp.auto_asconf_splist);
+ spin_unlock(&net->sctp.addr_wq_lock);
+ sp->do_auto_asconf = 1;
+ }
+}
+
/* Bind a local address either to an endpoint or to an association. */
static int sctp_do_bind(struct sock *sk, union sctp_addr *addr, int len)
{
@@ -418,8 +430,10 @@ static int sctp_do_bind(struct sock *sk,
return -EADDRINUSE;

/* Refresh ephemeral port. */
- if (!bp->port)
+ if (!bp->port) {
bp->port = inet_sk(sk)->inet_num;
+ sctp_auto_asconf_init(sp);
+ }

/* Add the address to the bind address list.
* Use GFP_ATOMIC since BHs will be disabled.
@@ -4993,19 +5007,6 @@ 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,
- &net->sctp.auto_asconf_splist);
- sp->do_auto_asconf = 1;
- spin_unlock(&sock_net(sk)->sctp.addr_wq_lock);
- } else {
- sp->do_auto_asconf = 0;
- }
-
local_bh_enable();

return 0;
@@ -9401,6 +9402,8 @@ static int sctp_sock_migrate(struct sock
return err;
}

+ sctp_auto_asconf_init(newsp);
+
/* Move any messages in the old socket's receive queue that are for the
* peeled off association to the new socket's receive queue.
*/