PlainSocketImpl: Create marker_fd lazily

At the class initialization time, PlainSocketImpl created a socketPair()
file descriptor which it uses to pre-close other file descriptors. In
Android, this file descriptor is created within the zygote, and leaks to
zygote's children, crossing a security boundary and generating SELinux
denials.

Rather than creating a file descriptor and never closing it, create the
file descriptor only when it's needed. This prevents the file descriptor
from leaking from zygote to zygote's children.

Another possible approach - to maintain a single file descriptor for
every process. This approach has couple of issues with it:
1) The zygote doesn't allow any open file descriptor created using
socketPair() while forking a process, therefore, it should be
dup2-ed to a whitelisted fd before the fork so that it doesn't recycle
during the fork process, and after the process, it should again have
to be a valid marker_fd. The whole process may introduce issues.
2) marker_fd will always be opened even though no socket is using it.

Bug: 27376593
Test: cts-tradefed run cts -m CtsLibcoreTestCases \
       -t libcore.java.net.ConcurrentCloseTest

Change-Id: I7caee120de5f5399b767c7a5fc69ef4a20538646

0 files changed, 0 insertions, 0 deletions