Reopen whitelisted zygote file descriptors after a fork.
We don't want these descriptors to be shared post-fork, so we'll
have to close and reopen them when the zygote forks. The set of
open descriptors is checked against a whitelist and it is a fatal
error if a non whitelisted FD is opened. It is also a fatal error
if anything other than a regular file / character device or socket
is opened at the time of forking.
This work is done in two stages :
- An initial list of FDs is constructed and cached prior to the
first zygote fork.
- On each subsequent fork, we check whether the list of open FDs
has changed. We are currently tolerant of changes, but in the
longer term, it should be a fatal error if the set of open file
descriptors in the zygote changes.
- Post fork, we traverse the list of open descriptors and reopen
them if necessary.
bug:
30963384
Change-Id: Icfd45c96c660491b554d146a9d70d97dbcc712bc