In the Linux kernel, the following vulnerability has been resolved:
userfaultfd: fix a race between writeprotect and exit_mmap() A race is
possible when a process exits, its VMAs are removed by exit_mmap() and at
the same time userfaultfd_writeprotect() is called. The race was detected
by KASAN on a development kernel, but it appears to be possible on vanilla
kernels as well. Use mmget_not_zero() to prevent the race as done in other
userfaultfd operations.
git.kernel.org/linus/cb185d5f1ebf900f4ae3bf84cee212e6dd035aca (5.15-rc7)
git.kernel.org/stable/c/149958ecd0627a9f1e9c678c25c665400054cd6a
git.kernel.org/stable/c/3cda4bfffd4f755645577aaa9e96a606657b4525
git.kernel.org/stable/c/cb185d5f1ebf900f4ae3bf84cee212e6dd035aca
launchpad.net/bugs/cve/CVE-2021-47461
nvd.nist.gov/vuln/detail/CVE-2021-47461
security-tracker.debian.org/tracker/CVE-2021-47461
www.cve.org/CVERecord?id=CVE-2021-47461