From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CC9301836F9 for ; Wed, 26 Jun 2024 14:56:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719413776; cv=none; b=Pr3KWferLRaWvLQ7QkNRI8KgKCA0NuVbtZcteKFDXoH2hO/BdTlWTc3qZFYuK1c/khpSEgWiyyIUUlOAIDx9NTcvsloWu6lfmI8b3ByQR9kqcwYV+mS2wQpoSboyyP/WZ84E3yDyqYUx7mvqq4cS1wFX6RIRIR3bxhw6Blyrkqs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719413776; c=relaxed/simple; bh=qcpv/PEkN7/dnb9WgjxI74Dt2WxRgk6JL9ZvdSkmrTU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=DJtj5udoOUxvP1LyyTstc0KHMN00y+he2LsmOLyLuoTUv9hzUeogXAUwYGpAOIFCDKJaw7hsSUma6LCN8VtW+DVQbggUPISoPtuCscb+z3+/Uutq+d1v4MRNvO3/w3PS5NBHbnMhTIHq5uY3bZz+9gZchn+1cpIoxNTSw3ZNxVw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=XF4Pigsi; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="XF4Pigsi" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1719413773; 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=tgH2VmVylsgvJB0IG2XE9dX80Rg9UYW9RXvREHo32vo=; b=XF4PigsiKk1MzIhD2qBTK2H2mjvwNWK7BdsRVeZiYywY0LmLRy8mGjPfxraH4t8hVgQp8A /RCr786eAc4bG4NxT0Pvme78ES/Hu0AbSV5BH/LJL+ZkrqW4YmlaEOpkYgLlkgRjrS+blc Td7U3CoZZ/spVqLgT1hzXa51pZEvr98= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-201-KAkyj4uvPMehwgcU63vvKw-1; Wed, 26 Jun 2024 10:56:12 -0400 X-MC-Unique: KAkyj4uvPMehwgcU63vvKw-1 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4D16A1956096; Wed, 26 Jun 2024 14:56:10 +0000 (UTC) Received: from [10.22.16.126] (unknown [10.22.16.126]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 5FE60300070E; Wed, 26 Jun 2024 14:56:08 +0000 (UTC) Message-ID: <7cc422b6-8437-455a-9d3f-718b4504ae9a@redhat.com> Date: Wed, 26 Jun 2024 10:56:07 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V3] cgroup/cpuset: Prevent UAF in proc_cpuset_show() To: Chen Ridong , tj@kernel.org, lizefan.x@bytedance.com, hannes@cmpxchg.org, adityakali@google.com, sergeh@kernel.org, mkoutny@suse.com Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org References: <20240626094101.472912-1-chenridong@huawei.com> Content-Language: en-US From: Waiman Long In-Reply-To: <20240626094101.472912-1-chenridong@huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On 6/26/24 05:41, Chen Ridong wrote: > An UAF can happen when /proc/cpuset is read as reported in [1]. > > This can be reproduced by the following methods: > 1.add an mdelay(1000) before acquiring the cgroup_lock In the > cgroup_path_ns function. > 2.$cat /proc//cpuset repeatly. > 3.$mount -t cgroup -o cpuset cpuset /sys/fs/cgroup/cpuset/ > $umount /sys/fs/cgroup/cpuset/ repeatly. > > The race that cause this bug can be shown as below: > > (umount) | (cat /proc//cpuset) > css_release | proc_cpuset_show > css_release_work_fn | css = task_get_css(tsk, cpuset_cgrp_id); > css_free_rwork_fn | cgroup_path_ns(css->cgroup, ...); > cgroup_destroy_root | mutex_lock(&cgroup_mutex); > rebind_subsystems | > cgroup_free_root | > | // cgrp was freed, UAF > | cgroup_path_ns_locked(cgrp,..); > > When the cpuset is initialized, the root node top_cpuset.css.cgrp > will point to &cgrp_dfl_root.cgrp. In cgroup v1, the mount operation will > allocate cgroup_root, and top_cpuset.css.cgrp will point to the allocated > &cgroup_root.cgrp. When the umount operation is executed, > top_cpuset.css.cgrp will be rebound to &cgrp_dfl_root.cgrp. > > The problem is that when rebinding to cgrp_dfl_root, there are cases > where the cgroup_root allocated by setting up the root for cgroup v1 > is cached. This could lead to a Use-After-Free (UAF) if it is > subsequently freed. The descendant cgroups of cgroup v1 can only be > freed after the css is released. However, the css of the root will never > be released, yet the cgroup_root should be freed when it is unmounted. > This means that obtaining a reference to the css of the root does > not guarantee that css.cgrp->root will not be freed. > > Fix this problem by using rcu_read_lock in proc_cpuset_show(). > As cgroup root_list is already RCU-safe, css->cgroup is safe. > This is similar to commit 9067d90006df ("cgroup: Eliminate the > need for cgroup_mutex in proc_cgroup_show()") > > [1] https://syzkaller.appspot.com/bug?extid=9b1ff7be974a403aa4cd > > Fixes: a79a908fd2b0 ("cgroup: introduce cgroup namespaces") > Signed-off-by: Chen Ridong > --- > kernel/cgroup/cpuset.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index c12b9fdb22a4..7f4536c9ccce 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -21,6 +21,7 @@ > * License. See the file COPYING in the main directory of the Linux > * distribution for more details. > */ > +#include "cgroup-internal.h" > > #include > #include > @@ -5052,8 +5053,15 @@ int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns, > goto out; > > css = task_get_css(tsk, cpuset_cgrp_id); > - retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX, > - current->nsproxy->cgroup_ns); > + rcu_read_lock(); > + spin_lock_irq(&css_set_lock); > + /* In case the root has already been unmounted */ > + if (css->cgroup) > + retval = cgroup_path_ns_locked(css->cgroup, buf, PATH_MAX, > + current->nsproxy->cgroup_ns); > + > + spin_unlock_irq(&css_set_lock); > + rcu_read_unlock(); > css_put(css); > if (retval == -E2BIG) > retval = -ENAMETOOLONG; Reviewed-by: Waiman Long