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Subject: Re: [PATCH v5 1/7] fs: introduce kernel_pread_file* support
From:   Scott Branden <scott.branden@broadcom.com>
To:     Mimi Zohar <zohar@kernel.org>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        David Brown <david.brown@linaro.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Shuah Khan <shuah@kernel.org>, bjorn.andersson@linaro.org,
        Shuah Khan <skhan@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>
Cc:     "Rafael J . Wysocki" <rafael@kernel.org>,
        linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-fsdevel@vger.kernel.org,
        BCM Kernel Feedback <bcm-kernel-feedback-list@broadcom.com>,
        Olof Johansson <olof@lixom.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Colin Ian King <colin.king@canonical.com>,
        Kees Cook <keescook@chromium.org>,
        Takashi Iwai <tiwai@suse.de>, linux-kselftest@vger.kernel.org,
        Andy Gross <agross@kernel.org>,
        linux-security-module <linux-security-module@vger.kernel.org>,
        linux-integrity <linux-integrity@vger.kernel.org>
References: <20200508002739.19360-1-scott.branden@broadcom.com>
 <20200508002739.19360-2-scott.branden@broadcom.com>
 <1589395153.5098.158.camel@kernel.org>
 <0e6b5f65-8c61-b02e-7d35-b4ae52aebcf3@broadcom.com>
Message-ID: <104a1eea-6b55-d857-04b9-d13aed9a36fd@broadcom.com>
Date:   Wed, 13 May 2020 11:57:09 -0700
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On 2020-05-13 11:53 a.m., Scott Branden wrote:
> Hi Mimi,
>
> On 2020-05-13 11:39 a.m., Mimi Zohar wrote:
>> [Cc'ing linux-security-module, linux-integrity]
>>
>> On Thu, 2020-05-07 at 17:27 -0700, Scott Branden wrote:
>>> Add kernel_pread_file* support to kernel to allow for partial read
>>> of files with an offset into the file.  Existing kernel_read_file
>>> functions call new kernel_pread_file functions with offset=0 and
>>> flags=KERNEL_PREAD_FLAG_WHOLE.
>>>
>>> Signed-off-by: Scott Branden <scott.branden@broadcom.com>
>>> ---
>> <snip>
>>
>>> @@ -941,14 +955,16 @@ int kernel_read_file(struct file *file, void 
>>> **buf, loff_t *size,
> The checkpatch shows this as kernel_read_file when it is actually the 
> new function kernel_pread_file.
typo: "checkpatch" should be "patch diff"
> Please see the call to kernel_pread_file from kernel_read_file in the 
> complete patch rather this snippet.
>>>             if (bytes == 0)
>>>               break;
>>> +
>>> +        buf_pos += bytes;
>>>       }
>>>   -    if (pos != i_size) {
>>> +    if (pos != read_end) {
>>>           ret = -EIO;
>>>           goto out_free;
>>>       }
>>>   -    ret = security_kernel_post_read_file(file, *buf, i_size, id);
>>> +    ret = security_kernel_post_read_file(file, *buf, alloc_size, id);
>>>       if (!ret)
>>>           *size = pos;
>> Prior to the patch set that introduced this security hook, firmware
>> would be read twice, once for measuring/appraising the firmware and
>> again reading the file contents into memory.  Partial reads will break
>> both IMA's measuring the file and appraising the file signatures.
> The partial file read support is needed for request_firmware_into_buf 
> from drivers.  The EXPORT_SYMBOL_GPL is being removed so that
> there can be no abuse of the partial file read support.  Such file 
> integrity checks are not needed for this use case.  The partial file 
> (firmware image) is actually downloaded in portions and verified on 
> the device it is loaded to.
>
> Regards,
>  Scott