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 [masami: Backport patch from 4.9. Adjust to use current_user_ns() to get current user_ns. Fix conflict in cgroup_release_agent_write().] Reference: CVE-2022-0492 Signed-off-by: Masami Ichikawa(CIP) masami.ichikawa@cybertrust.co.jp --- kernel/cgroup.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 1f5e7dcbfd40..af521a3da21c 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -1786,6 +1786,13 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data) 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 && + ((current_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;

@@ -2135,6 +2142,16 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, goto out_unlock; }

+ /* + * Release agent gets called with all capabilities, + * require capabilities to set release agent. + */ + if (opts.release_agent && + ((current_user_ns() != &init_user_ns) || !capable(CAP_SYS_ADMIN))) { + ret = -EINVAL; + goto out_unlock; + } + root = kzalloc(sizeof(*root), GFP_KERNEL); if (!root) { ret = -ENOMEM; @@ -2839,6 +2856,14 @@ static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,

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); if (!cgrp) return -ENODEV;