Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752646AbeAAO1v (ORCPT + 1 other); Mon, 1 Jan 2018 09:27:51 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:42260 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752574AbeAAO1t (ORCPT ); Mon, 1 Jan 2018 09:27:49 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nicolas Dichtel , Kirill Tkhai , Andrey Ryabinin , "Eric W. Biederman" , Eric Dumazet , "David S. Miller" Subject: [PATCH 4.4 47/63] net: Fix double free and memory corruption in get_net_ns_by_id() Date: Mon, 1 Jan 2018 15:25:05 +0100 Message-Id: <20180101140050.428225389@linuxfoundation.org> X-Mailer: git-send-email 2.15.1 In-Reply-To: <20180101140042.456380281@linuxfoundation.org> References: <20180101140042.456380281@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: "Eric W. Biederman" [ Upstream commit 21b5944350052d2583e82dd59b19a9ba94a007f0 ] (I can trivially verify that that idr_remove in cleanup_net happens after the network namespace count has dropped to zero --EWB) Function get_net_ns_by_id() does not check for net::count after it has found a peer in netns_ids idr. It may dereference a peer, after its count has already been finaly decremented. This leads to double free and memory corruption: put_net(peer) rtnl_lock() atomic_dec_and_test(&peer->count) [count=0] ... __put_net(peer) get_net_ns_by_id(net, id) spin_lock(&cleanup_list_lock) list_add(&net->cleanup_list, &cleanup_list) spin_unlock(&cleanup_list_lock) queue_work() peer = idr_find(&net->netns_ids, id) | get_net(peer) [count=1] | ... | (use after final put) v ... cleanup_net() ... spin_lock(&cleanup_list_lock) ... list_replace_init(&cleanup_list, ..) ... spin_unlock(&cleanup_list_lock) ... ... ... ... put_net(peer) ... atomic_dec_and_test(&peer->count) [count=0] ... spin_lock(&cleanup_list_lock) ... list_add(&net->cleanup_list, &cleanup_list) ... spin_unlock(&cleanup_list_lock) ... queue_work() ... rtnl_unlock() rtnl_lock() ... for_each_net(tmp) { ... id = __peernet2id(tmp, peer) ... spin_lock_irq(&tmp->nsid_lock) ... idr_remove(&tmp->netns_ids, id) ... ... ... net_drop_ns() ... net_free(peer) ... } ... | v cleanup_net() ... (Second free of peer) Also, put_net() on the right cpu may reorder with left's cpu list_replace_init(&cleanup_list, ..), and then cleanup_list will be corrupted. Since cleanup_net() is executed in worker thread, while put_net(peer) can happen everywhere, there should be enough time for concurrent get_net_ns_by_id() to pick the peer up, and the race does not seem to be unlikely. The patch fixes the problem in standard way. (Also, there is possible problem in peernet2id_alloc(), which requires check for net::count under nsid_lock and maybe_get_net(peer), but in current stable kernel it's used under rtnl_lock() and it has to be safe. Openswitch begun to use peernet2id_alloc(), and possibly it should be fixed too. While this is not in stable kernel yet, so I'll send a separate message to netdev@ later). Cc: Nicolas Dichtel Signed-off-by: Kirill Tkhai Fixes: 0c7aecd4bde4 "netns: add rtnl cmd to add and get peer netns ids" Reviewed-by: Andrey Ryabinin Reviewed-by: "Eric W. Biederman" Signed-off-by: Eric W. Biederman Reviewed-by: Eric Dumazet Acked-by: Nicolas Dichtel Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/core/net_namespace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/net/core/net_namespace.c +++ b/net/core/net_namespace.c @@ -261,7 +261,7 @@ struct net *get_net_ns_by_id(struct net spin_lock_irqsave(&net->nsid_lock, flags); peer = idr_find(&net->netns_ids, id); if (peer) - get_net(peer); + peer = maybe_get_net(peer); spin_unlock_irqrestore(&net->nsid_lock, flags); rcu_read_unlock();