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

From: Scott Branden <scott.branden@broadcom.com>
To: Kees Cook <keescook@chromium.org>
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 13:35:17 -0700	[thread overview]
Message-ID: <9ba08503-e515-6761-63de-a3b611720b1b@broadcom.com> (raw)
In-Reply-To: <202007101543.912633AA73@keescook>

Hi Kees

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,
Scott