Re: [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@xxxxxxxxxxxx>
> > > ---
> > <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.
> > > Â ÂÂÂÂÂÂÂÂÂ if (bytes == 0)
> > > ÂÂÂÂÂÂÂÂÂÂÂÂÂ break;
> > > +
> > > +ÂÂÂÂÂÂÂ buf_pos += bytes;
> > > ÂÂÂÂÂ }
> > > Â -ÂÂÂ if (pos != i_size) {
> > > +ÂÂÂ if (pos != read_end) {
> > > ÂÂÂÂÂÂÂÂÂ ret = -EIO;
> > > ÂÂÂÂÂÂÂÂÂ goto out_free;
> > > ÂÂÂÂÂ }
> > > Â -ÂÂÂ ret = security_kernel_post_read_file(file, *buf, i_size, id);
> > > +ÂÂÂ ret = security_kernel_post_read_file(file, *buf, alloc_size, id);
> > > ÂÂÂÂÂ if (!ret)
> > > ÂÂÂÂÂÂÂÂÂ *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. ÂPartial 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,
> ÂScott