CVE-2021-47461 userfaultfd: fix a race between writeprotect and exit_mmap()

In the Linux kernel, the following vulnerability has been resolved: userfaultfd: fix a race between writeprotect and exitmmap A race is possible when a process exits, its VMAs are removed by exitmmap and at the same time userfaultfdwriteprotect is called. The race was detected by KASAN on a...