cgroup-v1: Require capabilities to set release_agent

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>

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 5456611874eb535f71f12f74b8ee6a1b7ca7f1b1..ced2b3f3547c61d7ac599367ce647672d8525dff 100644 (file)
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -577,6 +577,14 @@ 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, false);
        if (!cgrp)
                return -ENODEV;
@@ -1048,6 +1056,7 @@ static int cgroup1_remount(struct kernfs_root *kf_root, int *flags, char *data)
 {
        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;
 
@@ -1061,6 +1070,12 @@ static int cgroup1_remount(struct kernfs_root *kf_root, int *flags, char *data)
        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;
@@ -1224,6 +1239,15 @@ struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
                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) {