[PATCH 5.4 03/10] cgroup-v1: Require capabilities to set release_agent

Greg Kroah-Hartman
2022-02-04T09:20:55Z

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/cgroup/cgroup-v1.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -549,6 +549,14 @@ 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;
@@ -961,6 +969,12 @@ int cgroup1_parse_param(struct fs_contex
/* Specifying two release agents is forbidden */
if (ctx->release_agent)
return cg_invalf(fc, "cgroup1: release_agent respecified");
+ /*
+ * Release agent gets called with all capabilities,
+ * require capabilities to set release agent.
+ */
+ if ((fc->user_ns != &init_user_ns) || !capable(CAP_SYS_ADMIN))
+ return cg_invalf(fc, "cgroup1: Setting release_agent not allowed");
ctx->release_agent = param->string;
param->string = NULL;
break;