The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 467a726b754f474936980da793b4ff2ec3e382a7 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Michal=20Koutn=C3=BD?= mkoutny@suse.com Date: Thu, 17 Feb 2022 17:11:28 +0100 Subject: [PATCH] cgroup-v1: Correct privileges check in release_agent writes MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit

The idea is to check: a) the owning user_ns of cgroup_ns, b) capabilities in init_user_ns.

The commit 24f600856418 ("cgroup-v1: Require capabilities to set release_agent") got this wrong in the write handler of release_agent since it checked user_ns of the opener (may be different from the owning user_ns of cgroup_ns). Secondly, to avoid possibly confused deputy, the capability of the opener must be checked.

Fixes: 24f600856418 ("cgroup-v1: Require capabilities to set release_agent") Cc: stable@vger.kernel.org Link: https://lore.kernel.org/stable/20220216121142.GB30035@blackbody.suse.cz/ Signed-off-by: Michal Koutný mkoutny@suse.com Reviewed-by: Masami Ichikawa(CIP) masami.ichikawa@cybertrust.co.jp Signed-off-by: Tejun Heo tj@kernel.org

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c index 0e877dbcfeea..afc6c0e9c966 100644 --- a/kernel/cgroup/cgroup-v1.c +++ b/kernel/cgroup/cgroup-v1.c @@ -546,6 +546,7 @@ static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off) { struct cgroup *cgrp; + struct cgroup_file_ctx *ctx;

BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);

@@ -553,8 +554,9 @@ static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of, * Release agent gets called with all capabilities, * require capabilities to set release agent. */ - if ((of->file->f_cred->user_ns != &init_user_ns) || - !capable(CAP_SYS_ADMIN)) + ctx = of->priv; + if ((ctx->ns->user_ns != &init_user_ns) || + !file_ns_capable(of->file, &init_user_ns, CAP_SYS_ADMIN)) return -EPERM;

cgrp = cgroup_kn_lock_live(of->kn, false);