linux-ext4 - Re: [PATCH v15 3/9] libfs: Introduce case-insensitive string comparison helper

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Date: Tue, 2 Apr 2024 20:36:07 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: Eugen Hristev <eugen.hristev@...labora.com>
Cc: tytso@....edu, adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
	jaegeuk@...nel.org, chao@...nel.org,
	linux-f2fs-devel@...ts.sourceforge.net,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel@...labora.com, viro@...iv.linux.org.uk, brauner@...nel.org,
	jack@...e.cz, krisman@...e.de,
	Gabriel Krisman Bertazi <krisman@...labora.com>
Subject: Re: [PATCH v15 3/9] libfs: Introduce case-insensitive string
 comparison helper

On Tue, Apr 02, 2024 at 06:48:36PM +0300, Eugen Hristev wrote:
> +int generic_ci_match(const struct inode *parent,
> +		     const struct qstr *name,
> +		     const struct qstr *folded_name,
> +		     const u8 *de_name, u32 de_name_len)
> +{
> +	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 dirent = QSTR_INIT(de_name, de_name_len);
> +	int res = 0, match = 0;
> +
> +	if (IS_ENCRYPTED(parent)) {
> +		const struct fscrypt_str encrypted_name =
> +			FSTR_INIT((u8 *) de_name, de_name_len);
> +
> +		if (WARN_ON_ONCE(!fscrypt_has_encryption_key(parent)))
> +			return -EINVAL;
> +
> +		decrypted_name.name = kmalloc(de_name_len, GFP_KERNEL);
> +		if (!decrypted_name.name)
> +			return -ENOMEM;
> +		res = fscrypt_fname_disk_to_usr(parent, 0, 0, &encrypted_name,
> +						&decrypted_name);
> +		if (res < 0)
> +			goto out;
> +		dirent.name = decrypted_name.name;
> +		dirent.len = decrypted_name.len;
> +	}
> +
> +	/*
> +	 * Attempt a case-sensitive match first. It is cheaper and
> +	 * should cover most lookups, including all the sane
> +	 * applications that expect a case-sensitive filesystem.
> +	 */
> +	if (folded_name->name) {
> +		if (dirent.len == folded_name->len &&
> +		    !memcmp(folded_name->name, dirent.name, dirent.len)) {
> +			match = 1;
> +			goto out;
> +		}
> +		res = utf8_strncasecmp_folded(um, folded_name, &dirent);
> +	} else {
> +		if (dirent.len == name->len &&
> +		    !memcmp(name->name, dirent.name, dirent.len) &&
> +		    (!sb_has_strict_encoding(sb) || !utf8_validate(um, name))) {
> +			match = 1;
> +			goto out;
> +		}
> +		res = utf8_strncasecmp(um, name, &dirent);
> +	}

The 'match' variable is unnecessary because setting res=0 achieves the same
effect.

- Eric