From patchwork Mon Aug 3 13:06:27 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 11698049 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E030E13B6 for ; Mon, 3 Aug 2020 13:06:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C9874206D4 for ; Mon, 3 Aug 2020 13:06:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="RjyZ3Ao8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727783AbgHCNGk (ORCPT ); Mon, 3 Aug 2020 09:06:40 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:20726 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727081AbgHCNGj (ORCPT ); Mon, 3 Aug 2020 09:06:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596459998; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=j/v002Gxe6nBxuXIo8xXJ4Ruh4kteZD7I/mhEJxj0MM=; b=RjyZ3Ao8Syde3weKNYgQsl25WnyUN9COSbZLFr9/hCio/dzvHf0tp8azb/W8GvXXytjip1 rpPQG4zNGiOQozsD81U7mYUT0aKnNGYtb+y8DsS5e5JLCGY5zOBAqrMyyUc6gnqH5zCvzR ZwLeka/K9/KUvIUenL4Ce65d7HuKr0U= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-421-NWK5erupNA6dLy11xyeTNg-1; Mon, 03 Aug 2020 09:06:34 -0400 X-MC-Unique: NWK5erupNA6dLy11xyeTNg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 29543106B20A; Mon, 3 Aug 2020 13:06:32 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-112-32.rdu2.redhat.com [10.10.112.32]) by smtp.corp.redhat.com (Postfix) with ESMTP id 214D78A19E; Mon, 3 Aug 2020 13:06:27 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH 1/5] watch_queue: Limit the number of watches a user can hold [ver #2] From: David Howells To: viro@zeniv.linux.org.uk Cc: Linus Torvalds , Jarkko Sakkinen , dhowells@redhat.com, torvalds@linux-foundation.org, casey@schaufler-ca.com, sds@tycho.nsa.gov, nicolas.dichtel@6wind.com, raven@themaw.net, christian@brauner.io, jlayton@redhat.com, kzak@redhat.com, mszeredi@redhat.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Date: Mon, 03 Aug 2020 14:06:27 +0100 Message-ID: <159645998732.1779777.6694081988484186124.stgit@warthog.procyon.org.uk> In-Reply-To: <159645997768.1779777.8286723139418624756.stgit@warthog.procyon.org.uk> References: <159645997768.1779777.8286723139418624756.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.23 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: 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 --- 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 917d88edb7b9..a8ec3b6093fc 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 f74020f6bd9d..0ef8f65bd2d7 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);