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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 45F46C433FE for ; Thu, 16 Dec 2021 19:03:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240810AbhLPTDL (ORCPT ); Thu, 16 Dec 2021 14:03:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53182 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233828AbhLPTDK (ORCPT ); Thu, 16 Dec 2021 14:03:10 -0500 Received: from mail-wm1-x32d.google.com (mail-wm1-x32d.google.com [IPv6:2a00:1450:4864:20::32d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 180A2C061574 for ; Thu, 16 Dec 2021 11:03:10 -0800 (PST) Received: by mail-wm1-x32d.google.com with SMTP id p27-20020a05600c1d9b00b0033bf8532855so112273wms.3 for ; Thu, 16 Dec 2021 11:03:10 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to; bh=HXI05E/6oOg8+zg3Xq8L/JMKsTmaYdkr5+qDutJzX9A=; b=EYeWtODbLiOL5AupEALW8HJ4Y03vVeyYo/Js74DLkEbhWjU4XZyXlZpdvaKk9Sks7N OB/hfxuZ56LN+bSUw0vK4JMzNx9gPKwh774wcO2ZOm6MRzrgnIXrq+13dIXSNC7SzpT1 PE+sf16p+qpjItyeNdvs5DnjcPePZjWS/E9Jo3bpllb5LQLJouXM/wV3PeTGm2H/sewZ MdvS3wCJJSwGb3BmrCOsAUweTA+tqpd35jiX/ioWhl7LQ0vTbOcL4bPKf69oyk/1DECO S36VZHWRigowZv+qYEhCTMgiLgZjQK8hJcOcNuRYiVsn3QV5aO0u576OWbqfJsV18dKG Uvdw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=HXI05E/6oOg8+zg3Xq8L/JMKsTmaYdkr5+qDutJzX9A=; b=Wb0WBFIDiJDUoR1L20LsJQIZct5AvXTs6E69jW1lCN/L+KFUil+p8ayjppv7KTmlbV Y+LrMi+RS7B7jVXRbAZsXDOOGF3yDxZxKMk2lEJzs6/FI6lcHXk4mZQk+AhcEbWF/vcH Ujr3CNG+scS9retdt9iTOdrW0L4J/87IyOCMPsslSXSfty8cR3BeHAkkHlz5KmSsvh/a R2HXeJLqLMXE0G4JnXTsmZQOOmPPG/ScVsJuuRA9EVeA8tLdqVGKMqShopDX9lQ0F0Q7 CuFgAXNZbkRvNoslHBi8haBFsBqf2eMWp10OQk1PWx7ie281aWwfp88b7NaQjEgzdI1I URcg== X-Gm-Message-State: AOAM533x3pkZ+R0VBilE9QwTFa30wz9Wra56eSLeMF5ZsKGyG6eH9TP2 hdd8EoorkcHJw2qSsGuBm3JV1g== X-Google-Smtp-Source: ABdhPJwA5U0MGzpPuGgwV+mDNNPBbqJPJbvSTOkd0ZSRVhraJiiWQ6boXP4LJfkzRnRKugRYEbnplw== X-Received: by 2002:a05:600c:4153:: with SMTP id h19mr6471922wmm.142.1639681388621; Thu, 16 Dec 2021 11:03:08 -0800 (PST) Received: from google.com ([2.31.167.18]) by smtp.gmail.com with ESMTPSA id g13sm7475908wrd.57.2021.12.16.11.03.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Dec 2021 11:03:08 -0800 (PST) Date: Thu, 16 Dec 2021 19:03:02 +0000 From: Lee Jones To: Xin Long Cc: Jakub Kicinski , LKML , Vlad Yasevich , Neil Horman , Marcelo Ricardo Leitner , "David S. Miller" , lksctp developers , "H.P. Yarroll" , Karl Knutson , Jon Grimm , Xingang Guo , Hui Huang , Sridhar Samudrala , Daisy Chang , Ryan Layer , Kevin Gao , network dev Subject: Re: [RESEND 2/2] sctp: hold cached endpoints to prevent possible UAF Message-ID: References: <20211214215732.1507504-1-lee.jones@linaro.org> <20211214215732.1507504-2-lee.jones@linaro.org> <20211215174818.65f3af5e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 16 Dec 2021, Xin Long wrote: > ( > > On Thu, Dec 16, 2021 at 1:12 PM Xin Long wrote: > > > > On Thu, Dec 16, 2021 at 12:14 PM Lee Jones wrote: > > > > > > On Thu, 16 Dec 2021, Lee Jones wrote: > > > > > > > On Thu, 16 Dec 2021, Xin Long wrote: > > > > > > > > > On Thu, Dec 16, 2021 at 11:39 AM Lee Jones wrote: > > > > > > > > > > > > On Thu, 16 Dec 2021, Xin Long wrote: > > > > > > > > > > > > > On Wed, Dec 15, 2021 at 8:48 PM Jakub Kicinski wrote: > > > > > > > > > > > > > > > > On Tue, 14 Dec 2021 21:57:32 +0000 Lee Jones wrote: > > > > > > > > > The cause of the resultant dump_stack() reported below is a > > > > > > > > > dereference of a freed pointer to 'struct sctp_endpoint' in > > > > > > > > > sctp_sock_dump(). > > > > > > > > > > > > > > > > > > This race condition occurs when a transport is cached into its > > > > > > > > > associated hash table followed by an endpoint/sock migration to a new > > > > > > > > > association in sctp_assoc_migrate() prior to their subsequent use in > > > > > > > > > sctp_diag_dump() which uses sctp_for_each_transport() to walk the hash > > > > > > > > > table calling into sctp_sock_dump() where the dereference occurs. > > > > > > > > > > > > > in sctp_sock_dump(): > > > > > > > struct sock *sk = ep->base.sk; > > > > > > > ... <--[1] > > > > > > > lock_sock(sk); > > > > > > > > > > > > > > Do you mean in [1], the sk is peeled off and gets freed elsewhere? > > > > > > > > > > > > 'ep' and 'sk' are both switched out for new ones in sctp_sock_migrate(). > > > > > > > > > > > > > if that's true, it's still late to do sock_hold(sk) in your this patch. > > > > > > > > > > > > No, that's not right. > > > > > > > > > > > > The schedule happens *inside* the lock_sock() call. > > > > > Sorry, I don't follow this. > > > > > We can't expect when the schedule happens, why do you think this > > > > > can never be scheduled before the lock_sock() call? > > > > > > > > True, but I've had this running for hours and it hasn't reproduced. > > I understand, but it's a crash, we shouldn't take any risk that it > > will never happen. > > you may try to add a usleep() before the lock_sock call to reproduce it. > > > > > > > > > > Without this patch, I can reproduce this in around 2 seconds. > > > > > > > > The C-repro for this is pretty intense! > > > > > > > > If you want to be *sure* that a schedule will never happen, we can > > > > take a reference directly with: > > > > > > > > ep = sctp_endpoint_hold(tsp->asoc->ep); > > > > sk = sock_hold(ep->base.sk); > > > > > > > > Which was my original plan before I soak tested this submitted patch > > > > for hours without any sign of reproducing the issue. > > we tried to not export sctp_obj_hold/put(), that's why we had > > sctp_for_each_transport(). > > > > ep itself holds a reference of sk when it's alive, so it's weird to do > > these 2 together. > > > > > > > > > > > If the sock is peeled off or is being freed, we shouldn't dump this sock, > > > > > and it's better to skip it. > > > > > > > > I guess we can do that too. > > > > > > > > Are you suggesting sctp_sock_migrate() as the call site? > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c > > index 85ac2e901ffc..56ea7a0e2add 100644 > > --- a/net/sctp/socket.c > > +++ b/net/sctp/socket.c > > @@ -9868,6 +9868,7 @@ static int sctp_sock_migrate(struct sock *oldsk, > > struct sock *newsk, > > inet_sk_set_state(newsk, SCTP_SS_ESTABLISHED); > > } > > > > + sock_set_flag(oldsk, SOCK_RCU_FREE); > > release_sock(newsk); > > > > return 0; > > > > SOCK_RCU_FREE is set to the previous sk, so that this sk will not > > be freed between rcu_read_lock() and rcu_read_unlock(). > > > > > > > > Also, when are you planning on testing the flag? > > SOCK_RCU_FREE flag is used when freeing sk in sk_destruct(), > > and if it's set, it will be freed in the next grace period of RCU. > > > > > > > > Won't that suffer with the same issue(s)? > > diff --git a/net/sctp/diag.c b/net/sctp/diag.c > > index 7970d786c4a2..b4c4acd9e67e 100644 > > --- a/net/sctp/diag.c > > +++ b/net/sctp/diag.c > > @@ -309,16 +309,21 @@ static int sctp_tsp_dump_one(struct > > sctp_transport *tsp, void *p) > > > > static int sctp_sock_dump(struct sctp_transport *tsp, void *p) > > { > > - struct sctp_endpoint *ep = tsp->asoc->ep; > > struct sctp_comm_param *commp = p; > > - struct sock *sk = ep->base.sk; > > struct sk_buff *skb = commp->skb; > > struct netlink_callback *cb = commp->cb; > > const struct inet_diag_req_v2 *r = commp->r; > > struct sctp_association *assoc; > > + struct sctp_endpoint *ep; > > + struct sock *sk; > > int err = 0; > > > > + rcu_read_lock(); > > + ep = tsp->asoc->ep; > > + sk = ep->base.sk; > > lock_sock(sk); > Unfortunately, this isn't going to work, as lock_sock() may sleep, > and is not allowed to be called understand rcu_read_lock() :( Ah! How about my original solution of taking: tsp->asoc->ep ... directly? If it already holds the sk, we should be golden? -- Lee Jones [李琼斯] Senior Technical Lead - Developer Services Linaro.org │ Open source software for Arm SoCs Follow Linaro: Facebook | Twitter | Blog