cgroup-v1: Require capabilities to set release_agent

commit 24f6008 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 <[email protected]> Tested-by: Tabitha Sable <[email protected]> Fixes: 81a6a5c ("Task Control Groups: automatic userspace notification of idle cgroups") Cc: [email protected] # v2.6.24+ Signed-off-by: "Eric W. Biederman" <[email protected]> Signed-off-by: Tejun Heo <[email protected]> [mkoutny: Adjust for pre-fs_context, duplicate mount/remount check, drop log messages.] Acked-by: Michal Koutný <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
gatieme · Feb 11, 2022 · 939f8b4 · 939f8b4
1 parent 940b106
commit 939f8b4
Showing 1 changed file with 24 additions and 0 deletions.
diff --git 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) {