Description: posix-clock: fix use-after-free in __fput() when a chardev is removed but a file is still open
References:
 https://lore.kernel.org/linux-fsdevel/20191125125342.6189-1-vdronov@redhat.com/T/#u
 https://www.openwall.com/lists/oss-security/2020/04/21/2
Notes:
 bwh> This seems to have been present since dynamic POSIX clocks were
 bwh> added in 2.6.39.  The fix includes an ABI change.
 bwh> However, similar bugs have occurred and been fixed in the i2c,
 bwh> media, and watchdog subsystems.
Bugs:
upstream: released (5.5-rc5) [a33121e5487b424339636b25c35d3a180eaa5f5e]
4.19-upstream-stable: released (4.19.93) [0393b8720128d5b39db8523e5bfbfc689f18c37c]
4.9-upstream-stable: released (4.9.224) [89e8fc989feaac00bf1a7f9a766289422e2f5768]
3.16-upstream-stable: released (3.16.83) [5230ef61882d2d14deb846eb6b48370694816e4c]
sid: released (5.4.8-1)
4.19-buster-security: released (4.19.98-1)
4.9-stretch-security: released (4.9.228-1)
3.16-jessie-security: released (3.16.84-1)