From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3704AC4332F for ; Mon, 27 Sep 2021 17:20:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 20C4D61279 for ; Mon, 27 Sep 2021 17:20:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236441AbhI0RWG (ORCPT ); Mon, 27 Sep 2021 13:22:06 -0400 Received: from mail.kernel.org ([198.145.29.99]:35212 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237319AbhI0RST (ORCPT ); Mon, 27 Sep 2021 13:18:19 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 6398B61371; Mon, 27 Sep 2021 17:12:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1632762741; bh=Ldceq8DADxE4S2kzlI+02ioyl6fZEYp2GY74RXkXMz0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DzoqiOqsaqj2B+rDbdqIqaMiteoHq75t6iiEvW0oQV4qDqYIcMfVFdwLCoenznK4k 7tJ8OU5533eEbehg8edqgxMfn4mkt7bF81XcCVDpewYx7ETdaf1U//rG+xjaOtQHjd 6XMEgdGS2U+mGZvHpKYA/S601PzGwNARM2ZMr3TY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ido Schimmel , Petr Machata , David Ahern , "David S. Miller" Subject: [PATCH 5.14 035/162] nexthop: Fix division by zero while replacing a resilient group Date: Mon, 27 Sep 2021 19:01:21 +0200 Message-Id: <20210927170234.694692941@linuxfoundation.org> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20210927170233.453060397@linuxfoundation.org> References: <20210927170233.453060397@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Ido Schimmel commit 563f23b002534176f49524b5ca0e1d94d8906c40 upstream. The resilient nexthop group torture tests in fib_nexthop.sh exposed a possible division by zero while replacing a resilient group [1]. The division by zero occurs when the data path sees a resilient nexthop group with zero buckets. The tests replace a resilient nexthop group in a loop while traffic is forwarded through it. The tests do not specify the number of buckets while performing the replacement, resulting in the kernel allocating a stub resilient table (i.e, 'struct nh_res_table') with zero buckets. This table should never be visible to the data path, but the old nexthop group (i.e., 'oldg') might still be used by the data path when the stub table is assigned to it. Fix this by only assigning the stub table to the old nexthop group after making sure the group is no longer used by the data path. Tested with fib_nexthops.sh: Tests passed: 222 Tests failed: 0 [1] divide error: 0000 [#1] PREEMPT SMP KASAN CPU: 0 PID: 1850 Comm: ping Not tainted 5.14.0-custom-10271-ga86eb53057fe #1107 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014 RIP: 0010:nexthop_select_path+0x2d2/0x1a80 [...] Call Trace: fib_select_multipath+0x79b/0x1530 fib_select_path+0x8fb/0x1c10 ip_route_output_key_hash_rcu+0x1198/0x2da0 ip_route_output_key_hash+0x190/0x340 ip_route_output_flow+0x21/0x120 raw_sendmsg+0x91d/0x2e10 inet_sendmsg+0x9e/0xe0 __sys_sendto+0x23d/0x360 __x64_sys_sendto+0xe1/0x1b0 do_syscall_64+0x35/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae Cc: stable@vger.kernel.org Fixes: 283a72a5599e ("nexthop: Add implementation of resilient next-hop groups") Signed-off-by: Ido Schimmel Reviewed-by: Petr Machata Reviewed-by: David Ahern Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/ipv4/nexthop.c | 2 ++ 1 file changed, 2 insertions(+) --- a/net/ipv4/nexthop.c +++ b/net/ipv4/nexthop.c @@ -1982,6 +1982,8 @@ static int replace_nexthop_grp(struct ne rcu_assign_pointer(old->nh_grp, newg); if (newg->resilient) { + /* Make sure concurrent readers are not using 'oldg' anymore. */ + synchronize_net(); rcu_assign_pointer(oldg->res_table, tmp_table); rcu_assign_pointer(oldg->spare->res_table, tmp_table); }