From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753255AbbDGIzt (ORCPT ); Tue, 7 Apr 2015 04:55:49 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:48174 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751028AbbDGIzr (ORCPT ); Tue, 7 Apr 2015 04:55:47 -0400 Date: Tue, 7 Apr 2015 10:55:44 +0200 From: Greg Kroah-Hartman To: Daniel Baluta Cc: Tom Van Braeckel , Rusty Russell , lguest , Linux Kernel Mailing List , kbuild test robot , lkp@01.org Subject: Re: [PATCH] lguest: explicitly setup /dev/lguest private_data Message-ID: <20150407085544.GA18078@kroah.com> References: <20150406121022.GA3867@wfg-t540p.sh.intel.com> <1428394698-16938-1-git-send-email-tomvanbraeckel@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 07, 2015 at 11:34:25AM +0300, Daniel Baluta wrote: > On Tue, Apr 7, 2015 at 11:18 AM, Tom Van Braeckel > wrote: > > The private_data member of the /dev/lguest device file is used to hold > > the current struct lguest and needs to be set to NULL to signify that > > no initialization has taken place. > > > > We explicitly set it to NULL to be independent of whatever value the > > misc subsystem initializes it to. > > > > Signed-off-by: Tom Van Braeckel > > --- > > Backstory: > > ========== > > The misc subsystem used to initialize a file's private_data to point to > > the misc device when a driver had registered a custom open file > > operation and initialized it to NULL when a custom open file operation > > had *not* been provided. > > > > This subtle quirk was confusing, to the point where kernel code > > registered *empty* file open operations to have private_data point to > > the misc device structure. > > > > And it lead to bugs, where the addition or removal of a custom open > > file operation surprisingly changed the initial contents of a file's > > private_data structure. > > > > The misc subsystem is currently underdoing changes to *always* set > > private_data to point to the misc device instead of only doing this > > when a custom open file operation has been registered. > > > > Intel's 0day kernel testing robot discovered that the lguest driver > > depended on it implicitly being initialized to NULL, as Fengguang Wu > > reported. Thanks a lot for all the hard work! > > > > drivers/lguest/lguest_user.c | 14 +++++++++++++- > > 1 file changed, 13 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c > > index c4c6113..054bf70 100644 > > --- a/drivers/lguest/lguest_user.c > > +++ b/drivers/lguest/lguest_user.c > > @@ -98,6 +98,17 @@ static int trap(struct lg_cpu *cpu, const unsigned long __user *input) > > return 0; > > } > > > > +/* > > + * Set up the /dev/lguest file structure > > + * The file's private_data will hold the "struct lguest" after > > + * initialization and is used to check whether it is already initialized. > > + */ > > +static int open(struct inode *inode, struct file *file) > > +{ > > + file->private_data = NULL; > > + return 0; > > +} > > + > > /*L:040 > > * Once our Guest is initialized, the Launcher makes it run by reading > > * from /dev/lguest. > > @@ -405,10 +416,11 @@ static int close(struct inode *inode, struct file *file) > > * > > * We begin our understanding with the Host kernel interface which the Launcher > > * uses: reading and writing a character device called /dev/lguest. All the > > - * work happens in the read(), write() and close() routines: > > + * work happens in the open(), read(), write() and close() routines: > > */ > > static const struct file_operations lguest_fops = { > > .owner = THIS_MODULE, > > + .open = open, > > .release = close, > > .write = write, > > .read = read, > > Hmm, isn't this already fixed? > > https://lkml.org/lkml/2015/3/23/319 Ah, this might be a cross-tree issue then, the 0-day bot tested my tree without this change in it, and hit the problem. So all is good when we merge with Linus for 4.1-rc1. But to be "safe" I could queue this up to my tree as well, any objection to that? thanks, greg k-h