linux-kernel - Re: [PATCH v4 2/3] initramfs: read metadata from special file METADATA!!!

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Date:   Mon, 01 Jul 2019 08:54:12 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>, viro@...iv.linux.org.uk
Cc:     linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, initramfs@...r.kernel.org,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, bug-cpio@....org,
        zohar@...ux.vnet.ibm.com, silviu.vlasceanu@...wei.com,
        dmitry.kasatkin@...wei.com, takondra@...co.com, kamensky@...co.com,
        hpa@...or.com, arnd@...db.de, rob@...dley.net,
        james.w.mcmechan@...il.com, niveditas98@...il.com
Subject: Re: [PATCH v4 2/3] initramfs: read metadata from special file
 METADATA!!!

Hi Roberto,

> diff --git a/init/initramfs.c b/init/initramfs.c
> index 5de396a6aac0..862c03123de8 100644
> --- a/init/initramfs.c
> +++ b/init/initramfs.c

> +static int __init do_process_metadata(char *buf, int len, bool last)
> +{

Part of the problem in upstreaming CPIO xattr support has been the
difficulty in reading and understanding the initramfs code due to a
lack of comments.  At least for any new code, let's add some comments
to simplify the review.  In this case, understanding "last", before
reading the code, would help.

Mimi

> +	int ret = 0;
> +
> +	if (!metadata_buf) {
> +		metadata_buf_ptr = metadata_buf = kmalloc(body_len, GFP_KERNEL);
> +		if (!metadata_buf_ptr) {
> +			ret = -ENOMEM;
> +			goto out;
> +		}
> +
> +		metadata_len = body_len;
> +	}
> +
> +	if (metadata_buf_ptr + len > metadata_buf + metadata_len) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	memcpy(metadata_buf_ptr, buf, len);
> +	metadata_buf_ptr += len;
> +
> +	if (last)
> +		do_parse_metadata(previous_name_buf);
> +out:
> +	if (ret < 0 || last) {
> +		kfree(metadata_buf);
> +		metadata_buf = NULL;
> +		metadata = 0;
> +	}
> +
> +	return ret;
> +}
> +
>  static int __init do_copy(void)
>  {
>  	if (byte_count >= body_len) {
>  		if (xwrite(wfd, victim, body_len) != body_len)
>  			error("write error");
> +		if (metadata)
> +			do_process_metadata(victim, body_len, true);
>  		ksys_close(wfd);
>  		do_utime(vcollected, mtime);
>  		kfree(vcollected);
> @@ -458,6 +500,8 @@ static int __init do_copy(void)
>  	} else {
>  		if (xwrite(wfd, victim, byte_count) != byte_count)
>  			error("write error");
> +		if (metadata)
> +			do_process_metadata(victim, byte_count, false);
>  		body_len -= byte_count;
>  		eat(byte_count);
>  		return 1;
>