CVE-2021-47318

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

arch_topology: Avoid use-after-free for scale_freq_data

Currently topology_scale_freq_tick() (which gets called from scheduler_tick()) may end up using a pointer to struct scale_freq_data, which was previously cleared by topology_clear_scale_freq_source(), as there is no protection in place here. The users of topology_clear_scale_freq_source() though needs a guarantee that the previously cleared scale_freq_data isnt used anymore, so they can free the related resources.

Since topology_scale_freq_tick() is called from scheduler tick, we dont want to add locking in there. Use the RCU update mechanism instead (which is already used by the schedulers utilization update path) to guarantee race free updates here.

synchronize_rcu() makes sure that all RCU critical sections that started before it is called, will finish before it returns. And so the callers of topology_clear_scale_freq_source() dont need to worry about their callback getting called anymore.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/83150f5d05f065fb5c12c612f119015cabdcc124
• https://git.kernel.org/stable/c/ccdf7e073170886bc370c613e269de610a794c4a
• https://git.kernel.org/stable/c/83150f5d05f065fb5c12c612f119015cabdcc124
• https://git.kernel.org/stable/c/ccdf7e073170886bc370c613e269de610a794c4a