linux-kernel - Re: [PATCH 2/4] fs: Remove FIRMWARE_PREALLOC_BUFFER from kernel_read

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Message-ID: <20200710220411.GR12769@casper.infradead.org>
Date:   Fri, 10 Jul 2020 23:04:11 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Scott Branden <scott.branden@...adcom.com>
Cc:     Kees Cook <keescook@...omium.org>,
        James Morris <jmorris@...ei.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jessica Yu <jeyu@...nel.org>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Matthew Garrett <matthewgarrett@...gle.com>,
        David Howells <dhowells@...hat.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        KP Singh <kpsingh@...gle.com>, Dave Olsthoorn <dave@...aar.me>,
        Hans de Goede <hdegoede@...hat.com>,
        Peter Jones <pjones@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Boyd <stephen.boyd@...aro.org>,
        Paul Moore <paul@...l-moore.com>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH 2/4] fs: Remove FIRMWARE_PREALLOC_BUFFER from
 kernel_read_file() enums

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?