ctdb_io: fix use-after-free on invalid packets
Wolfgang saw a talloc complaint about using freed memory in ctdb_tcp_read_cb.
His fix was to remove the talloc_free() in that function, which causes
loops when a socket is closed (as it does not get removed from the event
system), eg:
netcat 192.168.1.2 4379 < /dev/null
The real bug is that when we have more than one pending packet in the
queue, we loop calling the callback without any safeguards should that
callback free the queue (as it tends to do on invalid packets). This
can be reproduced by sending more than one bogus packet at once:
# Length word at start: 4 == empty packet (assumed little endian)
/usr/bin/printf \\4\\0\\0\\0\\4\\0\\0\\0 > /tmp/pkt
netcat 192.168.1.2 4379 < /tmp/pkt
Using a destructor we can check if the callback frees us, and exit
immediately. Elsewhere, we return after the callback anyway.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>