cgroups: verify that hierarchies are non-empty

Fixes: #3881
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/lxc/cgroups/cgroup.h b/src/lxc/cgroups/cgroup.h
index cb2a9751a9810ac5dc29817df0e97848aac7b1d4..d057957b4463d96f9204cae6754aa9ab15c1bde7 100644 (file)
--- a/src/lxc/cgroups/cgroup.h
+++ b/src/lxc/cgroups/cgroup.h
@@ -326,6 +326,9 @@ static inline int prepare_cgroup_ctx(struct cgroup_ops *ops,
 {
        __u32 idx;
 
+       if (!ops || !ops->hierarchies)
+               return ret_errno(ENOENT);
+
        for (idx = 0; ops->hierarchies[idx]; idx++) {
                if (idx >= CGROUP_CTX_MAX_FD)
                        return ret_errno(E2BIG);