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

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Date:   Tue, 11 Feb 2020 22:06:42 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Al Viro <viro@...iv.linux.org.uk>
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 Wed, Feb 12, 2020 at 05:55:11AM +0000, Al Viro wrote:
> 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).

After the patch earlier in the series that created generic_ci_d_compare() and
switched f2fs to use it, f2fs_ci_compare() is only called when the filesystem is
actually searching a directory, not from ->d_compare().  So the names and
parent->d_inode are stable in it.

But, that also means the GFP_ATOMIC isn't needed, and f2fs_ci_compare() should
be made 'static'.

- Eric