From patchwork Thu Apr 14 13:14:15 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 561555 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 52596C35273 for ; Thu, 14 Apr 2022 14:10:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245191AbiDNOHz (ORCPT ); Thu, 14 Apr 2022 10:07:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43174 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347707AbiDNN7a (ORCPT ); Thu, 14 Apr 2022 09:59:30 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0FB50BB0AD; Thu, 14 Apr 2022 06:51:57 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 9E99C61E2F; Thu, 14 Apr 2022 13:51:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A6DAEC385A1; Thu, 14 Apr 2022 13:51:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649944316; bh=lyLBJJG9Dgaoq9jiwGkE6UHnyGwQW6C3/SkxPDoKQrE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=eF9xMYdUJ3S0On8Mb698GUDbjSEiay0dq425Ft4ysoudxmGS5MnO7R3ivRBHdOu0l PzJbavly+JDZxNyCpmp2ByD6Cd74CCzUB/aAM9VqqJK/dP0+tTdbROvDlF6uSlDfD2 m3Zy5Qb68sCEhdM337njs96jNrO3T2V8dPefs03o= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg Kroah-Hartman , "Eric W. Biederman" , Linus Torvalds , =?utf-8?q?Michal_Koutn=C3=BD?= , Oleg Nesterov , syzbot+50f5cf33a284ce738b62@syzkaller.appspotmail.com, Tejun Heo , Ovidiu Panait Subject: [PATCH 5.4 470/475] cgroup: Use open-time cgroup namespace for process migration perm checks Date: Thu, 14 Apr 2022 15:14:15 +0200 Message-Id: <20220414110908.209753133@linuxfoundation.org> X-Mailer: git-send-email 2.35.2 In-Reply-To: <20220414110855.141582785@linuxfoundation.org> References: <20220414110855.141582785@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Tejun Heo commit e57457641613fef0d147ede8bd6a3047df588b95 upstream. cgroup process migration permission checks are performed at write time as whether a given operation is allowed or not is dependent on the content of the write - the PID. This currently uses current's cgroup namespace which is a potential security weakness as it may allow scenarios where a less privileged process tricks a more privileged one into writing into a fd that it created. This patch makes cgroup remember the cgroup namespace at the time of open and uses it for migration permission checks instad of current's. Note that this only applies to cgroup2 as cgroup1 doesn't have namespace support. This also fixes a use-after-free bug on cgroupns reported in https://lore.kernel.org/r/00000000000048c15c05d0083397@google.com Note that backporting this fix also requires the preceding patch. Reported-by: "Eric W. Biederman" Suggested-by: Linus Torvalds Cc: Michal Koutný Cc: Oleg Nesterov Reviewed-by: Michal Koutný Reported-by: syzbot+50f5cf33a284ce738b62@syzkaller.appspotmail.com Link: https://lore.kernel.org/r/00000000000048c15c05d0083397@google.com Fixes: 5136f6365ce3 ("cgroup: implement "nsdelegate" mount option") Signed-off-by: Tejun Heo [mkoutny: v5.10: duplicate ns check in procs/threads write handler, adjust context] Signed-off-by: Michal Koutný Signed-off-by: Greg Kroah-Hartman [OP: backport to v5.4: drop changes to cgroup_attach_permissions() and cgroup_css_set_fork(), adjust cgroup_procs_write_permission() calls] Signed-off-by: Ovidiu Panait Signed-off-by: Greg Kroah-Hartman --- kernel/cgroup/cgroup-internal.h | 2 ++ kernel/cgroup/cgroup.c | 24 +++++++++++++++++------- 2 files changed, 19 insertions(+), 7 deletions(-) --- a/kernel/cgroup/cgroup-internal.h +++ b/kernel/cgroup/cgroup-internal.h @@ -68,6 +68,8 @@ static inline struct cgroup_fs_context * struct cgroup_pidlist; struct cgroup_file_ctx { + struct cgroup_namespace *ns; + struct { void *trigger; } psi; --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -3758,14 +3758,19 @@ static int cgroup_file_open(struct kernf ctx = kzalloc(sizeof(*ctx), GFP_KERNEL); if (!ctx) return -ENOMEM; + + ctx->ns = current->nsproxy->cgroup_ns; + get_cgroup_ns(ctx->ns); of->priv = ctx; if (!cft->open) return 0; ret = cft->open(of); - if (ret) + if (ret) { + put_cgroup_ns(ctx->ns); kfree(ctx); + } return ret; } @@ -3776,13 +3781,14 @@ static void cgroup_file_release(struct k if (cft->release) cft->release(of); + put_cgroup_ns(ctx->ns); kfree(ctx); } static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off) { - struct cgroup_namespace *ns = current->nsproxy->cgroup_ns; + struct cgroup_file_ctx *ctx = of->priv; struct cgroup *cgrp = of->kn->parent->priv; struct cftype *cft = of->kn->priv; struct cgroup_subsys_state *css; @@ -3796,7 +3802,7 @@ static ssize_t cgroup_file_write(struct */ if ((cgrp->root->flags & CGRP_ROOT_NS_DELEGATE) && !(cft->flags & CFTYPE_NS_DELEGATABLE) && - ns != &init_cgroup_ns && ns->root_cset->dfl_cgrp == cgrp) + ctx->ns != &init_cgroup_ns && ctx->ns->root_cset->dfl_cgrp == cgrp) return -EPERM; if (cft->write) @@ -4772,9 +4778,9 @@ static int cgroup_procs_show(struct seq_ static int cgroup_procs_write_permission(struct cgroup *src_cgrp, struct cgroup *dst_cgrp, - struct super_block *sb) + struct super_block *sb, + struct cgroup_namespace *ns) { - struct cgroup_namespace *ns = current->nsproxy->cgroup_ns; struct cgroup *com_cgrp = src_cgrp; struct inode *inode; int ret; @@ -4810,6 +4816,7 @@ static int cgroup_procs_write_permission static ssize_t cgroup_procs_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off) { + struct cgroup_file_ctx *ctx = of->priv; struct cgroup *src_cgrp, *dst_cgrp; struct task_struct *task; const struct cred *saved_cred; @@ -4836,7 +4843,8 @@ static ssize_t cgroup_procs_write(struct */ saved_cred = override_creds(of->file->f_cred); ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp, - of->file->f_path.dentry->d_sb); + of->file->f_path.dentry->d_sb, + ctx->ns); revert_creds(saved_cred); if (ret) goto out_finish; @@ -4859,6 +4867,7 @@ static void *cgroup_threads_start(struct static ssize_t cgroup_threads_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off) { + struct cgroup_file_ctx *ctx = of->priv; struct cgroup *src_cgrp, *dst_cgrp; struct task_struct *task; const struct cred *saved_cred; @@ -4887,7 +4896,8 @@ static ssize_t cgroup_threads_write(stru */ saved_cred = override_creds(of->file->f_cred); ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp, - of->file->f_path.dentry->d_sb); + of->file->f_path.dentry->d_sb, + ctx->ns); revert_creds(saved_cred); if (ret) goto out_finish;