From: "Eric W. Biederman" ebiederm@xmission.com

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.

[ Upstream commit 24f6008564183aa120d07c03d9289519c2fe02af ]

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 ---

Hello, FWIW, I'm sharing v4.12 backport of the aforementioned patch (v4.12 is not actual stable but someone may find it useful).

Michal

kernel/cgroup/cgroup-v1.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+)

--- a/kernel/cgroup/cgroup-v1.c +++ b/kernel/cgroup/cgroup-v1.c @@ -531,6 +531,14 @@ 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; @@ -1004,6 +1012,7 @@ static int cgroup1_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;

@@ -1017,6 +1026,12 @@ static int cgroup1_remount(struct kernfs if (opts.subsys_mask != root->subsys_mask || opts.release_agent) pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n", task_tgid_nr(current), current->comm); + /* See cgroup1_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; @@ -1180,6 +1195,15 @@ struct dentry *cgroup1_mount(struct file ret = -EPERM; 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) {