From: Xin Long <lucien.xin@gmail.com>
Date: Sun, 2 May 2021 21:11:42 +0000 (+0800)
Subject: sctp: delay auto_asconf init until binding the first addr
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=89e55e90c09c6e712c7254467c077802dfd99eaa;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git

sctp: delay auto_asconf init until binding the first addr

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>
---

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index c0fe647dd4ac..09a99c92c27d 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -367,6 +367,18 @@ 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)
 {
@@ -429,8 +441,10 @@ 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.
@@ -4262,19 +4276,6 @@ 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;
@@ -7817,6 +7818,8 @@ 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.
 	 */