Re: [PATCH]: disassociate tty locking fixups

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

Ar Sad, 2006-10-14 am 07:22 -0400, ysgrifennodd Prarit Bhargava:
> Additional tty_mutex locking in do_tty_hangup and disassociate_ctty.  It is
> possible that do_tty_hangup sets current->signal->tty = NULL.  If that
> happens then disassociate_ctty can corrupt memory.

Ugly but I don't think the patches are sufficient. Firstly you need to
hold the task lock if you are poking around some other users ->signal,
or that may itself change. (disassociate_ctty seems to have this wrong)

Secondly you appear to have lock ordering issues (you lock tty_mutex in
both orders relative to the task list lock) (you take tty_mutex first,
then the task lock which is correct, but then you drop and retake the
tty_mutex while holding the task lock, which may deadlock)

Can you also explain why the ctty change proposed is neccessary ?

NAK the actual code, provisionally agree with the basic diagnosis of
insufficient locking.