cgroup-v1: Correct privileges check in release_agent writes

The idea is to check: a) the owning user_ns of cgroup_ns, b) capabilities in init_user_ns. The commit 24f6008 ("cgroup-v1: Require capabilities to set release_agent") got this wrong in the write handler of release_agent since it checked user_ns of the opener (may be different from the owning user_ns of cgroup_ns). Secondly, to avoid possibly confused deputy, the capability of the opener must be checked. Fixes: 24f6008 ("cgroup-v1: Require capabilities to set release_agent") Cc: [email protected] Link: https://lore.kernel.org/stable/[email protected]/ Signed-off-by: Michal Koutný <[email protected]> Reviewed-by: Masami Ichikawa(CIP) <[email protected]> Signed-off-by: Tejun Heo <[email protected]>
torvalds · Feb 22, 2022 · 467a726 · 467a726
1 parent 6d3971d
commit 467a726
Showing 1 changed file with 4 additions and 2 deletions.
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
@@ -546,15 +546,17 @@ static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
 					  char *buf, size_t nbytes, loff_t off)
 {
 	struct cgroup *cgrp;
+	struct cgroup_file_ctx *ctx;
 
 	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))
+	ctx = of->priv;
+	if ((ctx->ns->user_ns != &init_user_ns) ||
+	    !file_ns_capable(of->file, &init_user_ns, CAP_SYS_ADMIN))
 		return -EPERM;
 
 	cgrp = cgroup_kn_lock_live(of->kn, false);