linux-kernel - Re: [PATCH] coredump: Retry writes where appropriate

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20090603070939.4E31CFC333@magilla.sf.frob.com>
Date:	Wed,  3 Jun 2009 00:09:39 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, paul@...-scientist.net,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH] coredump: Retry writes where appropriate

> Oh, I forgot about freezer...

We all would like to.

> Well, not good to complicate recalc_sigpending_tsk() for this unlikely case.
> And this can't help, freezer does signal_wake_up() unconditionally.
> 
> So in fact this is another argument to check signal_pending() and clear it
> in dump_write/seek.

I can't agree with this at all.  IMHO it's far better to have a consistent
definition of when TIF_SIGPENDING ought to be triggered, and have
recalc_sigpending_tsk() use logic that matches the logic controlling when
to set TIF_SIGPENDING asynchronously (i.e. signal_wake_up calls).

> But since the coredumping task is not freezable anyway, perhaps we should
> change fake_signal_wake_up() to ignore SIGNAL_GROUP_DUMPING task.

That could be a long delay and a lot of i/o before suspending.

> Or we should make the coredumping freezable. This means dump_write/seek
> and exit_mm() should do try_to_freeze().

Yes, I think this is the thing to do for that issue.
(It's kind of a separate problem.)

> In any case, the coredumping is special. If ->write() returns -ERESTART/EINTR
> it assumes the return to ths user-space, this is not true for the coredump.
> This means that handling the spurious signals in coredump_file_write() is
> not so bad if we can't avoid this.

I am not so confident.  It seems far too easy to wind up with some other
way that TIF_SIGPENDING gets continually set and this loops, for example.
(This could be some day in the future when fs, driver or pipe-io code
changes somehow completely obscure.)  It's far better to have confidence
just in the signals code itself: the only things that set TIF_SIGPENDING
interlock with the logic of the only things that are expected to clear it.

Thanks,
Roland
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/