Re: [PATCH 2/4] fs: Remove FIRMWARE_PREALLOC_BUFFER from kernel_read_file() enums

From: Kees Cook <keescook@chromium.org>
To: Scott Branden <scott.branden@broadcom.com>
Cc: Matthew Wilcox <willy@infradead.org>,
	James Morris <jmorris@namei.org>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Mimi Zohar <zohar@linux.ibm.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Jessica Yu <jeyu@kernel.org>,
	Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Casey Schaufler <casey@schaufler-ca.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Matthew Garrett <matthewgarrett@google.com>,
	David Howells <dhowells@redhat.com>,
	Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	"Joel Fernandes (Google)" <joel@joelfernandes.org>,
	KP Singh <kpsingh@google.com>, Dave Olsthoorn <dave@bewaar.me>,
	Hans de Goede <hdegoede@redhat.com>,
	Peter Jones <pjones@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Stephen Boyd <stephen.boyd@linaro.org>,
	Paul Moore <paul@paul-moore.com>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-integrity@vger.kernel.org,
	linux-security-module@vger.kernel.org
Subject: Re: [PATCH 2/4] fs: Remove FIRMWARE_PREALLOC_BUFFER from kernel_read_file() enums
Date: Thu, 16 Jul 2020 14:16:09 -0700
Message-ID: <202007161415.10D015477@keescook> (raw)
In-Reply-To: <9ba08503-e515-6761-63de-a3b611720b1b@broadcom.com>

On Thu, Jul 16, 2020 at 01:35:17PM -0700, Scott Branden wrote:
> On 2020-07-10 3:44 p.m., Kees Cook wrote:
> > On Fri, Jul 10, 2020 at 03:10:25PM -0700, Scott Branden wrote:
> > > 
> > > On 2020-07-10 3:04 p.m., Matthew Wilcox wrote:
> > > > On Fri, Jul 10, 2020 at 02:00:32PM -0700, Scott Branden wrote:
> > > > > > @@ -950,8 +951,8 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
> > > > > >     		goto out;
> > > > > >     	}
> > > > > > -	if (id != READING_FIRMWARE_PREALLOC_BUFFER)
> > > > > > -		*buf = vmalloc(i_size);
> > > > > > +	if (!*buf)
> > > > > The assumption that *buf is always NULL when id !=
> > > > > READING_FIRMWARE_PREALLOC_BUFFER doesn't appear to be correct.
> > > > > I get unhandled page faults due to this change on boot.
> > > > Did it give you a stack backtrace?
> > > Yes, but there's no requirement that *buf need to be NULL when calling this
> > > function.
> > > To fix my particular crash I added the following locally:
> > > 
> > > --- a/kernel/module.c
> > > +++ b/kernel/module.c
> > > @@ -3989,7 +3989,7 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char
> > > __user *, uargs, int, flags)
> > >   {
> > >       struct load_info info = { };
> > >       loff_t size;
> > > -    void *hdr;
> > > +    void *hdr = NULL;
> > >       int err;
> > > 
> > >       err = may_init_module();
> > Thanks for the diagnosis and fix! I haven't had time to cycle back
> > around to this series yet. Hopefully soon. :)
> > 
> In order to assist in your patchset I have combined it with my patch series
> here:
> https://github.com/sbranden/linux/tree/kernel_read_file_for_kees
> 
> Please let me know if this matches your expectations for my patches or if
> there is something else I need to change.

Thanks! I was working on the next revision of this last night, and I'm
trying to get through today's email to finish it. I'll take a look!

-- 
Kees Cook