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 X-Spam-Level: X-Spam-Status: No, score=-13.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1EB2AC433E1 for ; Mon, 24 Aug 2020 08:36:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EAF3A22B3F for ; Mon, 24 Aug 2020 08:36:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598258192; bh=TMcgGpj0HK5jtl7J2jbGq1Bs+4VVnmcgR1udoAv4ziQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=T7htCBkLYDTOoOBh69HEL1R2hKaslpfp6ldnhCtiDQw+zxTtboayXkczwtVnYavPC QZ+qkQwIq089NrZqEu3CRSqy8fH1Rq0o+cIMTI9Btp0LoGR8/cX24w1k4Le/q53U/c jDM+5Iu+liVVYgjElS++vr60afLUpwnlDPfHuRYE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726548AbgHXIga (ORCPT ); Mon, 24 Aug 2020 04:36:30 -0400 Received: from mail.kernel.org ([198.145.29.99]:48564 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728253AbgHXIgP (ORCPT ); Mon, 24 Aug 2020 04:36:15 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1BA1C206F0; Mon, 24 Aug 2020 08:36:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598258174; bh=TMcgGpj0HK5jtl7J2jbGq1Bs+4VVnmcgR1udoAv4ziQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TO4XS+GqaP2sMJvZYDLFTuY2+QvtPHMX+ERdJQxuQZsJhiHZnhXG0+m6FSYOzgdWf t/zjBZQ4hUI1+FJPIDJmFcJw26D+b6VCy7ARtwJhipp9wEl7PF0wq2bOoBNtBgMwXk zHMrcmCEbfAQ2AeDCYYl4kRPs0ucGSNqOpxR0xA4= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Linus Torvalds , David Howells , Jarkko Sakkinen , Sasha Levin Subject: [PATCH 5.8 102/148] watch_queue: Limit the number of watches a user can hold Date: Mon, 24 Aug 2020 10:30:00 +0200 Message-Id: <20200824082418.916968691@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200824082413.900489417@linuxfoundation.org> References: <20200824082413.900489417@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: David Howells [ Upstream commit 29e44f4535faa71a70827af3639b5e6762d8f02a ] Impose a limit on the number of watches that a user can hold so that they can't use this mechanism to fill up all the available memory. This is done by putting a counter in user_struct that's incremented when a watch is allocated and decreased when it is released. If the number exceeds the RLIMIT_NOFILE limit, the watch is rejected with EAGAIN. This can be tested by the following means: (1) Create a watch queue and attach it to fd 5 in the program given - in this case, bash: keyctl watch_session /tmp/nlog /tmp/gclog 5 bash (2) In the shell, set the maximum number of files to, say, 99: ulimit -n 99 (3) Add 200 keyrings: for ((i=0; i<200; i++)); do keyctl newring a$i @s || break; done (4) Try to watch all of the keyrings: for ((i=0; i<200; i++)); do echo $i; keyctl watch_add 5 %:a$i || break; done This should fail when the number of watches belonging to the user hits 99. (5) Remove all the keyrings and all of those watches should go away: for ((i=0; i<200; i++)); do keyctl unlink %:a$i; done (6) Kill off the watch queue by exiting the shell spawned by watch_session. Fixes: c73be61cede5 ("pipe: Add general notification queue support") Reported-by: Linus Torvalds Signed-off-by: David Howells Reviewed-by: Jarkko Sakkinen Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- include/linux/sched/user.h | 3 +++ kernel/watch_queue.c | 8 ++++++++ 2 files changed, 11 insertions(+) diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h index 917d88edb7b9d..a8ec3b6093fcb 100644 --- a/include/linux/sched/user.h +++ b/include/linux/sched/user.h @@ -36,6 +36,9 @@ struct user_struct { defined(CONFIG_NET) || defined(CONFIG_IO_URING) atomic_long_t locked_vm; #endif +#ifdef CONFIG_WATCH_QUEUE + atomic_t nr_watches; /* The number of watches this user currently has */ +#endif /* Miscellaneous per-user rate limit */ struct ratelimit_state ratelimit; diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c index f74020f6bd9d5..0ef8f65bd2d71 100644 --- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -393,6 +393,7 @@ static void free_watch(struct rcu_head *rcu) struct watch *watch = container_of(rcu, struct watch, rcu); put_watch_queue(rcu_access_pointer(watch->queue)); + atomic_dec(&watch->cred->user->nr_watches); put_cred(watch->cred); } @@ -452,6 +453,13 @@ int add_watch_to_object(struct watch *watch, struct watch_list *wlist) watch->cred = get_current_cred(); rcu_assign_pointer(watch->watch_list, wlist); + if (atomic_inc_return(&watch->cred->user->nr_watches) > + task_rlimit(current, RLIMIT_NOFILE)) { + atomic_dec(&watch->cred->user->nr_watches); + put_cred(watch->cred); + return -EAGAIN; + } + spin_lock_bh(&wqueue->lock); kref_get(&wqueue->usage); kref_get(&watch->usage); -- 2.25.1