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 AB8BDC4332F for ; Thu, 16 Dec 2021 18:12:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240572AbhLPSMe (ORCPT ); Thu, 16 Dec 2021 13:12:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41486 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231582AbhLPSMd (ORCPT ); Thu, 16 Dec 2021 13:12:33 -0500 Received: from mail-oi1-x22b.google.com (mail-oi1-x22b.google.com [IPv6:2607:f8b0:4864:20::22b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A19ABC061574; Thu, 16 Dec 2021 10:12:32 -0800 (PST) Received: by mail-oi1-x22b.google.com with SMTP id q25so160596oiw.0; Thu, 16 Dec 2021 10:12:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=uAqIgqpgAc1PNcQxs6Z1Q9KRR9I+nC8P1ZUS5oFDdMo=; b=RowhSE9yVrp0J4do2S5MlxnCudbS7JjDCSk8ikVrsxRhYEpBAk+RLvP0ph51nS3OrZ 96YveMixUItM99ua9/UwGMebN18D7ESKeKWElWT9cWUG9MDzDXWsxodsGXtKUWpThgxN PT2J7AiTyKT+07WoO7bCmeXIExbAb97uxh+7JJyMM9xyR60Or4sOI1LCiBe2Rcsp54fn fneXEA0itNVnX6sxJo7hEqXxEmfD4KN8TyXL2CyN7qT42Y33cIB//6RfelwSs1n4Pua8 EAvX+bL8vVz3egz8mKSw4XQRt1WxXwOrRCZq+LkEBMTf3gd5fZ6fqpEsU6WXXyBV//Sh +hrA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=uAqIgqpgAc1PNcQxs6Z1Q9KRR9I+nC8P1ZUS5oFDdMo=; b=rpTjv2p44Z5lZC8tluXj6dW5LZTwcqjW95OdwI2FJRSa0I5Li7y4ZI1b6Cxg6kLg+6 DKpIw33F6wpSDUrjEMD8VaIfHk4cc4BxIJAiXMPW4tytIaoZlq+fWTtujzEdupD+cAsd 0l2reYJmZCYfSmqKHdyhJyV93qpoNPqZ4NnA2thEaadQ6E78KA4/ixb29cr2GcysHRCj NFhhTsjaulekkiYKm/5voOVALJcQvvxLPMj8uqEYLUg5wsqdiLQyS0vR0lqLVFQL81ov 4PMytwDJXaZmAb4QIu5HC5367i2RGAQD/wF01KZ7pwRXaCUkK9I/REzoTwaYu/NMTzQ7 X4VA== X-Gm-Message-State: AOAM532meUllkeEbocIVZN+QcEnEF/qQLpVxOl/NvPjRvbNBBhh1lSko 75W3HGiAb3asr0bh9Mo1XuwN9KnZeuJ1Na55mSg= X-Google-Smtp-Source: ABdhPJy7hj1K0C16CO5y+Is33GX1gjQQeIjqo2Oeema6LapZX7efpwR08jsn6Yi1jRP6OvaCkDmGnBYinuwkZ+tZQCc= X-Received: by 2002:a05:6808:10c9:: with SMTP id s9mr4994126ois.23.1639678351895; Thu, 16 Dec 2021 10:12:31 -0800 (PST) MIME-Version: 1.0 References: <20211214215732.1507504-1-lee.jones@linaro.org> <20211214215732.1507504-2-lee.jones@linaro.org> <20211215174818.65f3af5e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> In-Reply-To: From: Xin Long Date: Thu, 16 Dec 2021 13:12:20 -0500 Message-ID: Subject: Re: [RESEND 2/2] sctp: hold cached endpoints to prevent possible UAF To: Lee Jones 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 wro= te: > > > > > > > > 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 it= s > > > > > > > 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 occ= urs. > > > > > > > > > in sctp_sock_dump(): > > > > > struct sock *sk =3D 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_migra= te(). > > > > > > > > > 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 =3D sctp_endpoint_hold(tsp->asoc->ep); > > sk =3D 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 s= ock, > > > 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 =3D tsp->asoc->ep; struct sctp_comm_param *commp =3D p; - struct sock *sk =3D ep->base.sk; struct sk_buff *skb =3D commp->skb; struct netlink_callback *cb =3D commp->cb; const struct inet_diag_req_v2 *r =3D commp->r; struct sctp_association *assoc; + struct sctp_endpoint *ep; + struct sock *sk; int err =3D 0; + rcu_read_lock(); + ep =3D tsp->asoc->ep; + sk =3D ep->base.sk; lock_sock(sk); + if (tsp->asoc->ep !=3D ep) + goto release; list_for_each_entry(assoc, &ep->asocs, asocs) { if (cb->args[4] < cb->args[1]) goto next; @@ -358,6 +363,7 @@ static int sctp_sock_dump(struct sctp_transport *tsp, void *p) cb->args[4] =3D 0; release: release_sock(sk); + rcu_read_unlock(); return err; } rcu_read_lock() will make sure sk from tsp->asoc->ep->base.sk will not be freed until rcu_read_unlock(). That's all I have. Do you see any other way to fix this? Thanks. > > -- > Lee Jones [=E6=9D=8E=E7=90=BC=E6=96=AF] > Senior Technical Lead - Developer Services > Linaro.org =E2=94=82 Open source software for Arm SoCs > Follow Linaro: Facebook | Twitter | Blog