netdev - Re: Linux 4.2-rc6 regression: RIP: e030:[<ffffffff8110fb18>] [<ffffffff8110fb18>] detach_if

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: <alpine.DEB.2.11.1508172112370.3873@nanos>
Date:	Mon, 17 Aug 2015 21:13:35 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Sander Eikelenboom <linux@...elenboom.it>,
	Jon Christopherson <jon@...s.org>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	xen-devel@...ts.xen.org, david.vrabel@...rix.com
Subject: Re: Linux 4.2-rc6 regression: RIP: e030:[<ffffffff8110fb18>]
 [<ffffffff8110fb18>] detach_if_pending+0x18/0x80

On Mon, 17 Aug 2015, Eric Dumazet wrote:
> [PATCH] timer: fix a race in __mod_timer()
> 
> lock_timer_base() can not catch following :
> 
> CPU1 ( in __mod_timer()
> timer->flags |= TIMER_MIGRATING;
> spin_unlock(&base->lock);
> base = new_base;
> spin_lock(&base->lock);
> timer->flags &= ~TIMER_BASEMASK;
>                                   CPU2 (in lock_timer_base())
>                                   see timer base is cpu0 base
>                                   spin_lock_irqsave(&base->lock, *flags);
>                                   if (timer->flags == tf)
>                                        return base; // oops, wrong base
> timer->flags |= base->cpu // too late
> 
> We must write timer->flags in one go, otherwise we can fool other cpus.
> 
> Fixes: bc7a34b8b9eb ("timer: Reduce timer migration overhead if disabled")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> ---
>  kernel/time/timer.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> index 5e097fa9faf7..84190f02b521 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -807,8 +807,8 @@ __mod_timer(struct timer_list *timer, unsigned long expires,
>  			spin_unlock(&base->lock);
>  			base = new_base;
>  			spin_lock(&base->lock);
> -			timer->flags &= ~TIMER_BASEMASK;
> -			timer->flags |= base->cpu;
> +			WRITE_ONCE(timer->flags,
> +				   (timer->flags & ~TIMER_BASEMASK) | base->cpu);

Duh, yes. Picking it up for timers/urgent.

Thanks for spotting it.

       tglx
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html