Message-Id: <94980f802bdcec0fcc50f6e2add841ba70c311cc.1620752894.git.mkubecek@suse.cz>
From: Xin Long <lucien.xin@gmail.com>
Date: Mon, 3 May 2021 05:11:42 +0800
Subject: sctp: delay auto_asconf init until binding the first addr
Patch-mainline: v5.13-rc1
Git-commit: 34e5b01186858b36c4d7c87e1a025071e8e2401f
References: CVE-2021-23133 bsc#1184675

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>
Acked-by: Michal Kubecek <mkubecek@suse.cz>

---
 net/sctp/socket.c | 31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -353,6 +353,18 @@ static struct sctp_af *sctp_sockaddr_af(struct sctp_sock *opt,
 	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)
 {
@@ -415,8 +427,10 @@ static int sctp_do_bind(struct sock *sk, union sctp_addr *addr, int len)
 	}
 
 	/* 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.
@@ -4419,19 +4433,6 @@ 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,
-		    &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;
@@ -8130,6 +8131,8 @@ static void sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
 	sctp_bind_addr_dup(&newsp->ep->base.bind_addr,
 				&oldsp->ep->base.bind_addr, GFP_KERNEL);
 
+	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.
 	 */