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

[Al Viro <viro@zeniv.linux.org.uk>]

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).