linux-ext4 - Re: [PATCH v7 6/8] f2fs: Handle casefolding with Encryption

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Date:   Wed, 12 Feb 2020 05:55:11 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Daniel Rosenberg <drosen@...gle.com>,
        Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fscrypt@...r.kernel.org, Richard Weinberger <richard@....at>,
        linux-mtd@...ts.infradead.org,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        kernel-team@...roid.com
Subject: Re: [PATCH v7 6/8] f2fs: Handle casefolding with Encryption

On Tue, Feb 11, 2020 at 09:10:13PM -0800, Eric Biggers wrote:

> How about:
> 
> int f2fs_ci_compare(const struct inode *parent, const struct qstr *name,
> 		    u8 *de_name, size_t de_name_len, bool quick)
> {
> 	const struct super_block *sb = parent->i_sb;
> 	const struct unicode_map *um = sb->s_encoding;
> 	struct fscrypt_str decrypted_name = FSTR_INIT(NULL, de_name_len);
> 	struct qstr entry = QSTR_INIT(de_name, de_name_len);
> 	int ret;
> 
> 	if (IS_ENCRYPTED(parent)) {

oops.  parent->d_inode is unstable here; could have become NULL by that
point.

> 	if (quick)
> 		ret = utf8_strncasecmp_folded(um, name, &entry);
> 	else
> 		ret = utf8_strncasecmp(um, name, &entry);
> 	if (ret < 0) {
> 		/* Handle invalid character sequence as either an error
> 		 * or as an opaque byte sequence.
> 		 */

Really?  How would the callers possibly tell mismatch from an
error?  And if they could, would would they *do* with that
error, seeing that it might be an effect of a race with
rename()?

Again, ->d_compare() is NOT given a stable name.  Or *parent.  Or
(parent->d_inode).