linux-kernel - Re: [PATCH 20/26] ubifs: Add support for encrypted symlinks

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Message-ID: <20161021184231.GD90712@google.com>
Date:   Fri, 21 Oct 2016 11:42:31 -0700
From:   Eric Biggers <ebiggers@...gle.com>
To:     Richard Weinberger <richard@....at>
Cc:     linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, dedekind1@...il.com,
        adrian.hunter@...el.com, tytso@....edu, jaegeuk@...nel.org,
        david@...ma-star.at, wd@...x.de, sbabic@...x.de,
        dengler@...utronix.de
Subject: Re: [PATCH 20/26] ubifs: Add support for encrypted symlinks

On Fri, Oct 21, 2016 at 02:48:35PM +0200, Richard Weinberger wrote:
> +
> +	if (!dentry)
> +		return ERR_PTR(-ECHILD);
> +
> +	if (ubifs_crypt_is_encrypted(inode)) {
> +		err = fscrypt_get_encryption_info(inode);
> +		if (err)
> +			return ERR_PTR(err);
> +	} else
> +		return ui->data;
> +

This will make path lookups drop out of RCU mode when an unencrypted symlink is
followed.  This can be avoided by checking for unencrypted symlinks first:

	if (!ubifs_crypt_is_encrypted(inode))
		return ui->data;

	if (!dentry)
		return ERR_PTR(-ECHILD);

	err = fscrypt_get_encryption_info(inode);
	if (err)
		return ERR_PTR(err);

> +
> +	pstr.name[err] = '\0';
> +

In 4.9, fscrypt_fname_{disk_to_usr,usr_to_disk} return 0 instead of the output
length, so this will need to be changed to 'pstr.name[pstr.len] = '\0''.