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Date:   Sat, 8 Feb 2020 02:12:16 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Daniel Rosenberg <drosen@google.com>
Cc:     Theodore Ts'o <tytso@mit.edu>, linux-ext4@vger.kernel.org,
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Subject: Re: [PATCH v7 2/8] fs: Add standard casefolding support
Message-ID: <20200208021216.GE23230@ZenIV.linux.org.uk>
References: <20200208013552.241832-1-drosen@google.com>
 <20200208013552.241832-3-drosen@google.com>
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On Fri, Feb 07, 2020 at 05:35:46PM -0800, Daniel Rosenberg wrote:

> +int generic_ci_d_compare(const struct dentry *dentry, unsigned int len,
> +			  const char *str, const struct qstr *name)
> +{
> +	const struct dentry *parent = READ_ONCE(dentry->d_parent);
> +	const struct inode *inode = READ_ONCE(parent->d_inode);
> +	const struct super_block *sb = dentry->d_sb;
> +	const struct unicode_map *um = sb->s_encoding;
> +	struct qstr entry = QSTR_INIT(str, len);
> +	int ret;
> +
> +	if (!inode || !needs_casefold(inode))
> +		goto fallback;
> +
> +	ret = utf8_strncasecmp(um, name, &entry);

Again, is that safe in case when the contents of the string str points to
keeps changing under you?