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Subject: Re: [PATCH 06/13] fs/kernel_read_file: Remove redundant size argument
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>,
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        linux-fsdevel@vger.kernel.org, kexec@lists.infradead.org,
        linux-kernel@vger.kernel.org
References: <20200717174309.1164575-1-keescook@chromium.org>
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 <39b2d8af-812f-8c5e-3957-34543add0173@broadcom.com>
 <202007171502.22E12A4E9@keescook>
From:   Scott Branden <scott.branden@broadcom.com>
Message-ID: <99c58d32-da28-79ad-2fdb-83e0ca29660a@broadcom.com>
Date:   Fri, 17 Jul 2020 22:44:30 -0700
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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! :)
>