From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date: Fri, 31 May 2019 12:37:23 -0400

From: Willem de Bruijn <willemb@google.com>

Rollover used to use a complex RCU mechanism for assignment, which had
a race condition. The below patch fixed the bug and greatly simplified
the logic.

The feature depends on fanout, but the state is private to the socket.
Fanout_release returns f only when the last member leaves and the
fanout struct is to be freed.

Destroy rollover unconditionally, regardless of fanout state.

Fixes: 57f015f5eccf2 ("packet: fix crash in fanout_demux_rollover()")
Reported-by: syzbot <redacted>
Diagnosed-by: Dmitry Vyukov [off-list ref]
Signed-off-by: Willem de Bruijn <willemb@google.com>

Applied and queued up for -stable.