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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        syzbot+b9be979c55f2bea8ed30@syzkaller.appspotmail.com,
        David Howells <dhowells@redhat.com>
Subject: [PATCH 4.19 139/149] rxrpc: rxrpc_peer needs to hold a ref on the rxrpc_local record
Date:   Mon,  4 Nov 2019 22:45:32 +0100
Message-Id: <20191104212146.484170363@linuxfoundation.org>
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From: David Howells <dhowells@redhat.com>

commit 9ebeddef58c41bd700419cdcece24cf64ce32276 upstream.

The rxrpc_peer record needs to hold a reference on the rxrpc_local record
it points as the peer is used as a base to access information in the
rxrpc_local record.

This can cause problems in __rxrpc_put_peer(), where we need the network
namespace pointer, and in rxrpc_send_keepalive(), where we need to access
the UDP socket, leading to symptoms like:

    BUG: KASAN: use-after-free in __rxrpc_put_peer net/rxrpc/peer_object.c:411
    [inline]
    BUG: KASAN: use-after-free in rxrpc_put_peer+0x685/0x6a0
    net/rxrpc/peer_object.c:435
    Read of size 8 at addr ffff888097ec0058 by task syz-executor823/24216

Fix this by taking a ref on the local record for the peer record.

Fixes: ace45bec6d77 ("rxrpc: Fix firewall route keepalive")
Fixes: 2baec2c3f854 ("rxrpc: Support network namespacing")
Reported-by: syzbot+b9be979c55f2bea8ed30@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/rxrpc/peer_object.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/net/rxrpc/peer_object.c
+++ b/net/rxrpc/peer_object.c
@@ -220,7 +220,7 @@ struct rxrpc_peer *rxrpc_alloc_peer(stru
 	peer = kzalloc(sizeof(struct rxrpc_peer), gfp);
 	if (peer) {
 		atomic_set(&peer->usage, 1);
-		peer->local = local;
+		peer->local = rxrpc_get_local(local);
 		INIT_HLIST_HEAD(&peer->error_targets);
 		peer->service_conns = RB_ROOT;
 		seqlock_init(&peer->service_conn_lock);
@@ -311,7 +311,6 @@ void rxrpc_new_incoming_peer(struct rxrp
 	unsigned long hash_key;
 
 	hash_key = rxrpc_peer_hash_key(local, &peer->srx);
-	peer->local = local;
 	rxrpc_init_peer(rx, peer, hash_key);
 
 	spin_lock(&rxnet->peer_hash_lock);
@@ -421,6 +420,7 @@ static void __rxrpc_put_peer(struct rxrp
 	list_del_init(&peer->keepalive_link);
 	spin_unlock_bh(&rxnet->peer_hash_lock);
 
+	rxrpc_put_local(peer->local);
 	kfree_rcu(peer, rcu);
 }
 
@@ -454,6 +454,7 @@ void rxrpc_put_peer_locked(struct rxrpc_
 	if (n == 0) {
 		hash_del_rcu(&peer->hash_link);
 		list_del_init(&peer->keepalive_link);
+		rxrpc_put_local(peer->local);
 		kfree_rcu(peer, rcu);
 	}
 }