linux-kernel - Re: [GIT PULL] VFIO fixes for v4.1-rc2

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]

Date:	Fri, 1 May 2015 22:11:40 +0200
From:	Richard Weinberger <richard.weinberger@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>
Subject: Re: [GIT PULL] VFIO fixes for v4.1-rc2

On Fri, May 1, 2015 at 8:37 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> "flush_signals()" is only for kernel threads, where it's a hacky
> alternative to actually handling them (since kernel threads never
> rreturn to user space and cannot really "handle" a signal). But you're
> doing it in the ->remove handler for the device, which can be called
> by arbitrary system processes. This is not a kernel thread thing, as
> far as I can see.
>
> If you cannot handle signals, you damn well shouldn't be using
> "wait_event_interruptible_timeout()" to begin with. Get rid of the
> "interruptible", since it apparently *isn't* interruptible.
>
> So I'm not pulling this.
>
> Now I'm worried that other drivers do insane things like this. I
> wonder if we should add some sanity test to flush_signals() to make
> sure that it can only ever get called from a kernel thread.

Hmm, a quick grep exposes some questionable users.
At least w1 looks fishy.
drivers/w1/w1_family.c:w1_unregister_family
drivers/w1/w1_int.c:__w1_remove_master_device

What do you think about a WARN_ON like:

diff --git a/kernel/signal.c b/kernel/signal.c
index d51c5dd..b4079c3 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -427,6 +427,8 @@ void flush_signals(struct task_struct *t)
 {
        unsigned long flags;

+       WARN_ON((current->flags & PF_KTHREAD) == 0);
+
        spin_lock_irqsave(&t->sighand->siglock, flags);
        __flush_signals(t);
        spin_unlock_irqrestore(&t->sighand->siglock, flags);

-- 
Thanks,
//richard
--
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/