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;