[PATCH 4.9 1/2] cgroup-v1: Require capabilities to set release_agent

Greg Kroah-Hartman
2022-02-09T19:15:11Z

From: Eric W. Biederman <ebiederm@xmission.com>

commit 24f6008564183aa120d07c03d9289519c2fe02af upstream.

The cgroup release_agent is called with call_usermodehelper. The function
call_usermodehelper starts the release_agent with a full set fo capabilities.
Therefore require capabilities when setting the release_agaent.

Reported-by: Tabitha Sable <tabitha.c.sable@gmail.com>
Tested-by: Tabitha Sable <tabitha.c.sable@gmail.com>
Fixes: 81a6a5cdd2c5 ("Task Control Groups: automatic userspace notification of idle cgroups")
Cc: stable@vger.kernel.org # v2.6.24+
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
[mkoutny: Adjust for pre-fs_context, duplicate mount/remount check, drop log messages.]
Acked-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/cgroup.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)

--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1854,6 +1854,7 @@ static int cgroup_remount(struct kernfs_
{
int ret = 0;
struct cgroup_root *root = cgroup_root_from_kf(kf_root);
+ struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
struct cgroup_sb_opts opts;
u16 added_mask, removed_mask;

@@ -1873,6 +1874,13 @@ static int cgroup_remount(struct kernfs_
pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n",
task_tgid_nr(current), current->comm);

+ /* See cgroup_mount release_agent handling */
+ if (opts.release_agent &&
+ ((ns->user_ns != &init_user_ns) || !capable(CAP_SYS_ADMIN))) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+
added_mask = opts.subsys_mask & ~root->subsys_mask;
removed_mask = root->subsys_mask & ~opts.subsys_mask;

@@ -2248,6 +2256,16 @@ static struct dentry *cgroup_mount(struc
goto out_unlock;
}

+ /*
+ * Release agent gets called with all capabilities,
+ * require capabilities to set release agent.
+ */
+ if (opts.release_agent &&
+ ((ns->user_ns != &init_user_ns) || !capable(CAP_SYS_ADMIN))) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+
root = kzalloc(sizeof(*root), GFP_KERNEL);
if (!root) {
ret = -ENOMEM;
@@ -3026,6 +3044,14 @@ static ssize_t cgroup_release_agent_writ

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

+ /*
+ * 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))
+ return -EPERM;
+
cgrp = cgroup_kn_lock_live(of->kn, false);
if (!cgrp)
return -ENODEV;