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

[Mimi Zohar <zohar@kernel.org>]

[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,
>  
>  		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.

Mimi