s390/mm: Add NULL pointer check to crst_table_free() base_crst_free()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: s390/mm: Add NULL pointer check to crst_table_free() base_crst_free() crst_table_free() used to work with NULL pointers before the conversion to ptdescs. Since crst_table_free() can be called with a NULL pointer (error handling in crst_table_upgrade() add an explicit check. Also add the same check to base_crst_free() for consistency reasons. In real life this should not happen, since order two GFP_KERNEL allocations will not fail, unless FAIL_PAGE_ALLOC is enabled and used.

References

• https://git.kernel.org/stable/c/794fa52b94637d6b2e8c9474fbe3983af5c9f046
• https://git.kernel.org/stable/c/f80bd8bb6f380bc265834c46058d38b34174813e
• https://git.kernel.org/stable/c/b5efb63acf7bddaf20eacfcac654c25c446eabe8