Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

cpufreq: zero-initialize policy cpumask before sysfs publication

cpufreq_policy_alloc() allocates policy->cpus with alloc_cpumask_var(), i.e. without __GFP_ZERO, unlike the sibling related_cpus and real_cpus masks. With CONFIG_CPUMASK_OFFSTACK=y the mask is a separate kmalloc_node() allocation, so its bitmap holds whatever the slab allocator left behind:

cpufreq_online() cpufreq_policy_alloc() alloc_cpumask_var(&policy->cpus) /* bitmap is uninitialized */ kobject_init_and_add() /* policy%u/ appears in sysfs */ cpufreq_policy_online() cpumask_copy(policy->cpus, cpumask_of(cpu)) /* first valid value */

This leaves a window in which the sysfs attributes are already reachable while policy->cpus is still garbage. show()/store() gate on policy_is_inactive(), i.e. cpumask_empty(policy->cpus), so a non-zero bitmap makes them run the attribute callbacks on a policy that is not initialized yet.

Fix this by using zalloc_cpumask_var() for policy->cpus.