From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BD81933EC for ; Tue, 30 Apr 2024 07:20:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714461613; cv=none; b=GkE/FW3crdfvVzAAX2TZXc6xvkdndtFaATGG04JHSUYr9rZF63gzdW0YJDM+oSNC8YSttdFZMtOlwxsr88miT5ODiZ6Etr26WqzvYNW6mB0RsiDE82s9tGWzX/gfnIs/HDQQ7sMtw37sev9gp1WB1aJTD647G5BVGYnHq41Tkx8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714461613; c=relaxed/simple; bh=dDoRX0sFyMPB/yD48eqj4XKbmpiWrNu6eqDRZ+zd/rc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=dlXEBmwUzkwDj3lM5R+2QhHm4YvP14ZRvS8EgOj9SUTT+mZkKViIPI2dXKg9pRpPrBgn8psZ4AbdQhs0o3SpYskHLJrkys5YWPsRQTZPacEbZuX15fH7HtZPGQ0gaokzCNvMdMnqtyOLeDtokKKYdYkZIwvCVf2mplkhvJif4mM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=g0EpUuWy; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="g0EpUuWy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F0DFCC2BBFC; Tue, 30 Apr 2024 07:20:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1714461613; bh=dDoRX0sFyMPB/yD48eqj4XKbmpiWrNu6eqDRZ+zd/rc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=g0EpUuWyd5/69M77k9gSdkaLwaexYtvX6Bd7gLzbohIYjfC1BPsI63whTG99Gd4S6 iKJhqC45EmES+G6NTTjGQHDbeRzagFnv4IfFpPDV/wJ7THxPdz4aRGqK91vjAfgRLh 9XyZkG0UoDAUMY/HLfpfpz52YOBo82HO96/5orVE= Date: Tue, 30 Apr 2024 09:20:10 +0200 From: Greg Kroah-Hartman To: Dirk Behme Cc: linux-kernel@vger.kernel.org, Rafael J Wysocki , syzbot+ffa8143439596313a85a@syzkaller.appspotmail.com, Eugeniu Rosca Subject: Re: [PATCH] drivers: core: Make dev->driver usage safe in dev_uevent() Message-ID: <2024043030-remnant-plenty-1eeb@gregkh> References: <20240430045531.4062232-1-dirk.behme@de.bosch.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240430045531.4062232-1-dirk.behme@de.bosch.com> On Tue, Apr 30, 2024 at 06:55:31AM +0200, Dirk Behme wrote: > Inspired by the function dev_driver_string() in the same file make sure > in case of uninitialization dev->driver is used safely in dev_uevent(), > as well. I think you are racing and just getting "lucky" with your change here, just like dev_driver_string() is doing there (that READ_ONCE() really isn't doing much to protect you...) > This change is based on the observation of the following race condition: > > Thread #1: > ========== > > really_probe() { > ... > probe_failed: > ... > device_unbind_cleanup(dev) { > ... > dev->driver = NULL; // <= Failed probe sets dev->driver to NULL > ... > } > ... > } > > Thread #2: > ========== > > dev_uevent() { Wait, how can dev_uevent() be called if probe fails? Who is calling that? > ... > if (dev->driver) > // If dev->driver is NULLed from really_probe() from here on, > // after above check, the system crashes > add_uevent_var(env, "DRIVER=%s", dev->driver->name); > > dev_driver_string() can't be used here because we want NULL and not > anything else in the non-init case. > > Similar cases are reported by syzkaller in > > https://syzkaller.appspot.com/bug?extid=ffa8143439596313a85a > > But these are regarding the *initialization* of dev->driver > > dev->driver = drv; > > As this switches dev->driver to non-NULL these reports can be considered > to be false-positives (which should be "fixed" by this commit, as well, > though). > > Fixes: 239378f16aa1 ("Driver core: add uevent vars for devices of a class") > Cc: syzbot+ffa8143439596313a85a@syzkaller.appspotmail.com > Reviewed-by: Eugeniu Rosca > Tested-by: Eugeniu Rosca > Signed-off-by: Dirk Behme > --- > drivers/base/core.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/drivers/base/core.c b/drivers/base/core.c > index 5f4e03336e68..99ead727c08f 100644 > --- a/drivers/base/core.c > +++ b/drivers/base/core.c > @@ -2639,6 +2639,7 @@ static const char *dev_uevent_name(const struct kobject *kobj) > static int dev_uevent(const struct kobject *kobj, struct kobj_uevent_env *env) > { > const struct device *dev = kobj_to_dev(kobj); > + struct device_driver *drv; > int retval = 0; > > /* add device node properties if present */ > @@ -2667,8 +2668,12 @@ static int dev_uevent(const struct kobject *kobj, struct kobj_uevent_env *env) > if (dev->type && dev->type->name) > add_uevent_var(env, "DEVTYPE=%s", dev->type->name); > > - if (dev->driver) > - add_uevent_var(env, "DRIVER=%s", dev->driver->name); > + /* dev->driver can change to NULL underneath us because of unbinding > + * or failing probe(), so be careful about accessing it. > + */ > + drv = READ_ONCE(dev->driver); > + if (drv) > + add_uevent_var(env, "DRIVER=%s", drv->name); Again, you are just reducing the window here. Maybe a bit, but not all that much overall as there is no real lock present. So how is this actually solving anything? And who is calling a uevent on a device that is not probed properly? Userspace? Within the kernel? Something else? thanks, greg k-h