[PATCH v5 1/7] fs: introduce kernel_pread_file* support

[Scott Branden]

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 at 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