Description: Use-after-free in userfaultfd_event_wait_completion function in userfaultfd.c
References:
 https://bugzilla.redhat.com/show_bug.cgi?id=1523481
Notes:
 bwh> Introduced in 4.11 by commit 893e26e61d04 "userfaultfd: non-cooperative:
 bwh> Add fork() event".
Bugs:
upstream: released (4.14-rc4) [384632e67e0829deb8015ee6ad916b180049d252]
4.9-upstream-stable: N/A "Vulnerable code not present"
3.16-upstream-stable: N/A "Vulnerable code not present"
3.2-upstream-stable: N/A "Vulnerable code not present"
sid: released (4.13.10-1)
4.9-stretch-security: N/A "Vulnerable code not present"
3.16-jessie-security: N/A "Vulnerable code not present"
3.2-wheezy-security: N/A "Vulnerable code not present"