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 9C98CC433FE for ; Wed, 22 Dec 2021 10:58:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244323AbhLVK60 (ORCPT ); Wed, 22 Dec 2021 05:58:26 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41876 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240152AbhLVK6Y (ORCPT ); Wed, 22 Dec 2021 05:58:24 -0500 Received: from mail-wr1-x42b.google.com (mail-wr1-x42b.google.com [IPv6:2a00:1450:4864:20::42b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7452EC06173F for ; Wed, 22 Dec 2021 02:58:24 -0800 (PST) Received: by mail-wr1-x42b.google.com with SMTP id v7so4006952wrv.12 for ; Wed, 22 Dec 2021 02:58:24 -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=U6h7YYcmCz5aSPslRAoWARbne1uxxYH871pKs16mGxI=; b=HNZ6vYXZWGcMzsyVNenb3KauQgqFVyS/CLuy1hRAJASHNvkfSJy6+hZaYDEAyrKTS6 r9Z2fXTiUIAXMqx/K9BqkKUrcRtSm5o4t4muQiXlq8+Jv+r5VQpy9q4wleVOz/Q44CX6 u2owH4RvjqBI1VZyEGfzwrv7yqoqOA2/LrT5IvV7e1ufkzkUOZR9ljDxoW449ga3g6Sk nkBz1sSpufObR3J/ZED7CSeiKvCZj7J6+OpJlXCP1TrDlYCdSm2xv7svTE8tV4aMpVYW GZ42qMv2So7dp6zpuwg1N5mtFunZqMsqWw7h3vNo+YJk0LYKpP3d12rg+qG4lqGDcnzF bA9Q== 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=U6h7YYcmCz5aSPslRAoWARbne1uxxYH871pKs16mGxI=; b=g3flyNvNeVky8HpXHiT1OYnHeW/P/EVcTq+gUff9aSYr1LCqBn99IrQPV2Ha0GUcnX ugNtf4GkTmVOjW8CuZZuKCLLvHPtfeh8/XGSsgtc+QQnsSkbRIj0yctZNYmIefRnpJiY GLAjNArrVX5PpaA56oojwlKeS0zpNEt34aHLsWRcWKxQioRhBx4gOrhQHMnYukQReiY+ rMErMMw0dLhqctZsqmwHsZXu2fOTRAiRanmZMO5qCGnSoIvf2wnEM/LfjVaMmz8pkR/k K1PVUB2BuvXaroRAzvV8nlSiysizhcCgKjvsBKIv0aNUOv37mgqadHF++tMKVJw9KbSN SITw== X-Gm-Message-State: AOAM530o5BWv46Enc4A+c07NCeaIgbGua82odC538QlvZUTJb8Mf0rfq 9Ev0fDhrdksqXZf0IwtPKdRn1Q== X-Google-Smtp-Source: ABdhPJyOSVp8sAj2OcAANzZqIahTuMFEy50QW3HzbkXKtDFt2Nce5vaZ46zJGUzIOPX4msbYj8Yq2A== X-Received: by 2002:adf:e751:: with SMTP id c17mr1752270wrn.402.1640170702955; Wed, 22 Dec 2021 02:58:22 -0800 (PST) Received: from google.com ([2.31.167.18]) by smtp.gmail.com with ESMTPSA id v6sm4949293wmh.8.2021.12.22.02.58.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Dec 2021 02:58:22 -0800 (PST) Date: Wed, 22 Dec 2021 10:58:20 +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" , Hui Huang , network dev Subject: Re: [RESEND 2/2] sctp: hold cached endpoints to prevent possible UAF Message-ID: References: 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 Tue, 21 Dec 2021, Xin Long wrote: > On Mon, Dec 20, 2021 at 3:56 AM Lee Jones wrote: > > > > On Sun, 19 Dec 2021, Xin Long wrote: > > > > > On Thu, Dec 16, 2021 at 2:03 PM Lee Jones wrote: > > > > > > > > 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? > > > Both ep and sk could be destroyed at this moment. > > > you can't try to hold an object that has already been destroyed. > > > It holds the sk only when ep is still alive. > > > > > > I don't see a way to get this fix with the current transport hashtable. > > > I will change to use port hashtable to dump sock/asocs for this. > > > > Right. Cache invalidation is hard! > > > > Sure, if there is a better way, please go ahead. > Hi, Jones, > > Port hashtable doesn't work either as lock_sock can not be called > under spin_lock(). > > I posted another patch where this issue can be fixed by moving ep free > to call_rcu(). > It will be great if you are able to test it. I certainly will. -- Lee Jones [李琼斯] Senior Technical Lead - Developer Services Linaro.org │ Open source software for Arm SoCs Follow Linaro: Facebook | Twitter | Blog