fuse: Fix oops at process_init_reply()

fuse: Fix oops at process_init_reply()

BugLink: https://bugs.launchpad.net/bugs/1824553
syzbot is hitting NULL pointer dereference at process_init_reply().
This is because deactivate_locked_super() is called before response for
initial request is processed.

Fix this by aborting and waiting for all requests (including FUSE_INIT)
before resetting fc->sb.

Original patch by Tetsuo Handa <penguin-kernel@I-love.SKAURA.ne.jp>.

Reported-by: syzbot <syzbot+b62f08f4d5857755e3bc@syzkaller.appspotmail.com>
Fixes: e27c9d3877a0 ("fuse: fuse: add time_gran to INIT_OUT")
Cc: <stable@vger.kernel.org> # v3.19
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
(backported from commit e8f3bd773d22f488724dffb886a1618da85c2966)
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>