mm/damon/sysfs-schemes: free old damon_sysfs_scheme_filter->memcg_path on write

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: mm/damon/sysfs-schemes: free old damon_sysfs_scheme_filter->memcg_path on write memcg_path_store() assigns a newly allocated memory buffer to filter->memcg_path, without deallocating the previously allocated and assigned memory buffer. As a result, users can leak kernel memory by continuously writing a data to memcg_path DAMOS sysfs file. Fix the leak by deallocating the previously set memory buffer.

References

• https://git.kernel.org/stable/c/490a43d07f1663d827e802720d30cbc0494e4f81
• https://git.kernel.org/stable/c/c5d5b0047b0c0f304608f3824139f7bd34c48413
• https://git.kernel.org/stable/c/4a158ac0538dd5695eeaa00aa0720d711f3e4ef1
• https://git.kernel.org/stable/c/4f489fe6afb395dbc79840efa3c05440b760d883