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From: Scott Branden <scott.branden@broadcom.com>
To: Kees Cook <keescook@chromium.org>
Cc: Mimi Zohar <zohar@linux.ibm.com>,
	Matthew Wilcox <willy@infradead.org>,
	James Morris <jmorris@namei.org>,
	Luis Chamberlain <mcgrof@kernel.org>,
	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>,
	Stephen Smalley <stephen.smalley.work@gmail.com>,
	linux-security-module@vger.kernel.org,
	linux-integrity@vger.kernel.org, selinux@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, kexec@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 06/13] fs/kernel_read_file: Remove redundant size argument
Date: Fri, 17 Jul 2020 22:44:30 -0700
Message-ID: <99c58d32-da28-79ad-2fdb-83e0ca29660a@broadcom.com> (raw)
In-Reply-To: <202007171502.22E12A4E9@keescook>

Hi Kees,

On 2020-07-17 3:06 p.m., Kees Cook wrote:
> On Fri, Jul 17, 2020 at 12:04:18PM -0700, Scott Branden wrote:
>> On 2020-07-17 10:43 a.m., Kees Cook wrote:
>>> In preparation for refactoring kernel_read_file*(), remove the redundant
>>> "size" argument which is not needed: it can be included in the return
>> I don't think the size argument is redundant though.
>> The existing kernel_read_file functions always read the whole file.
>> Now, what happens if the file is bigger than the buffer.
>> How does kernel_read_file know it read the whole file by looking at the
>> return value?
> Yes; an entirely reasonable concern. This is why I add the file_size
> output argument later in the series.
There is something wrong with this patch.  I apply patches 1-5 and these 
pass the kernel self test.
Patch 6 does not pass the kernel-selftest/firmware/fw_run_tests.sh

>>> code, with callers adjusted. (VFS reads already cannot be larger than
>>> INT_MAX.)
>>> [...]
>>> -	if (i_size > SIZE_MAX || (max_size > 0 && i_size > max_size)) {
>>> +	if (i_size > INT_MAX || (max_size > 0 && i_size > max_size)) {
>> Should this be SSIZE_MAX?
> No, for two reasons: then we need to change the return value and likely
> the callers need more careful checks, and more importantly, because the
> VFS already limits single read actions to INT_MAX, so limits above this
> make no sense. Win win! :)
>


  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 17:42 [PATCH 00/13] Introduce partial kernel_read_file() support Kees Cook
2020-07-17 17:42 ` [PATCH 01/13] firmware_loader: EFI firmware loader must handle pre-allocated buffer Kees Cook
2020-07-17 19:08   ` Scott Branden
2020-07-17 17:42 ` [PATCH 02/13] fs/kernel_read_file: Remove FIRMWARE_PREALLOC_BUFFER enum Kees Cook
2020-07-17 19:09   ` Scott Branden
2020-07-17 17:42 ` [PATCH 03/13] fs/kernel_read_file: Remove FIRMWARE_EFI_EMBEDDED enum Kees Cook
2020-07-17 19:10   ` Scott Branden
2020-07-17 17:42 ` [PATCH 04/13] fs/kernel_read_file: Split into separate include file Kees Cook
2020-07-17 17:43 ` [PATCH 05/13] fs/kernel_read_file: Split into separate source file Kees Cook
2020-07-17 19:11   ` Scott Branden
2020-07-17 17:43 ` [PATCH 06/13] fs/kernel_read_file: Remove redundant size argument Kees Cook
2020-07-17 19:04   ` Scott Branden
2020-07-17 19:55     ` Scott Branden
2020-07-17 22:06     ` Kees Cook
2020-07-18  5:44       ` Scott Branden [this message]
2020-07-21 21:43   ` Scott Branden
2020-07-21 21:50     ` Kees Cook
2020-07-17 17:43 ` [PATCH 07/13] fs/kernel_read_file: Switch buffer size arg to size_t Kees Cook
2020-07-20  8:34   ` David Laight
2020-07-17 17:43 ` [PATCH 08/13] fs/kernel_read_file: Add file_size output argument Kees Cook
2020-07-17 17:43 ` [PATCH 09/13] LSM: Introduce kernel_post_load_data() hook Kees Cook
2020-07-17 17:43 ` [PATCH 10/13] firmware_loader: Use security_post_load_data() Kees Cook
2020-07-17 17:43 ` [PATCH 11/13] module: Call security_kernel_post_load_data() Kees Cook
2020-07-17 17:43 ` [PATCH 12/13] LSM: Add "contents" flag to kernel_read_file hook Kees Cook
2020-07-17 17:43 ` [PATCH 13/13] fs/kernel_file_read: Add "offset" arg for partial reads Kees Cook
2020-07-17 19:17 ` [PATCH 00/13] Introduce partial kernel_read_file() support Scott Branden
2020-07-17 22:10   ` Kees Cook

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