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

From: Scott Branden <scott.branden@broadcom.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Kees Cook <keescook@chromium.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: Fri, 10 Jul 2020 15:10:25 -0700	[thread overview]
Message-ID: <128120ca-7465-e041-7481-4c5d53f639dd@broadcom.com> (raw)
In-Reply-To: <20200710220411.GR12769@casper.infradead.org>



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();
>

