Re: [PATCH v12 3/8] libfs: Introduce case-insensitive string comparison helper

Gabriel Krisman Bertazi
2024-02-27T23:33:05Z

Eugen Hristev <eugen.hristev@collabora.com> writes:

> From: Gabriel Krisman Bertazi <krisman@collabora.com>
>
> generic_ci_match can be used by case-insensitive filesystems to compare
> strings under lookup with dirents in a case-insensitive way. This
> function is currently reimplemented by each filesystem supporting
> casefolding, so this reduces code duplication in filesystem-specific
> code.

Just a note that this conflicts with the other patchset to generic
helpers that I just applied. The conflict is trivial, If you could base
the next iteration on top of my for-next, it would be helpful.

>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
> [eugen.hristev@collabora.com: rework to first test the exact match]
> Signed-off-by: Eugen Hristev <eugen.hristev@collabora.com>
> ---
> fs/libfs.c | 85 ++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 4 +++
> 2 files changed, 89 insertions(+)
>
> diff --git a/fs/libfs.c b/fs/libfs.c
> index bb18884ff20e..65e2fb17a2b6 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -1773,6 +1773,91 @@ static const struct dentry_operations generic_ci_dentry_ops = {
> .d_hash = generic_ci_d_hash,
> .d_compare = generic_ci_d_compare,
> };
> +
> +/**
> + * generic_ci_match() - Match a name (case-insensitively) with a dirent.
> + * This is a filesystem helper for comparison with directory entries.
> + * generic_ci_d_compare should be used in VFS' ->d_compare instead.
> + *
> + * @parent: Inode of the parent of the dirent under comparison
> + * @name: name under lookup.
> + * @folded_name: Optional pre-folded name under lookup
> + * @de_name: Dirent name.
> + * @de_name_len: dirent name length.
> + *
> + * Test whether a case-insensitive directory entry matches the filename
> + * being searched. If @folded_name is provided, it is used instead of
> + * recalculating the casefold of @name.
> + *
> + * Return: > 0 if the directory entry matches, 0 if it doesn't match, or
> + * < 0 on error.
> + */
> +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, 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.

> + * This comparison is safe under RCU because the caller
> + * guarantees the consistency between str and len. See
> + * __d_lookup_rcu_op_compare() for details.

As I mentioned in the previous review, there's no RCU here. This comment
makes no sense here.

> + */
> + 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);
> + }
> +
> +out:

> + kfree(decrypted_name.name);
> + if (match) /* matched by direct comparison */
> + return 1;
> + else if (!res) /* matched by utf8 comparison */
> + return 1;
> + else if (res < 0) /* error on utf8 comparison */
> + return res;
> + return 0; /* no match */
> +}

It can be simplified to

if (res < 0)
return res;
return (match || !res);

>
> #ifdef CONFIG_FS_ENCRYPTION
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 820b93b2917f..7af691ff8d44 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3296,6 +3296,10 @@ extern int generic_file_fsync(struct file *, loff_t, loff_t, int);
> extern int generic_check_addressable(unsigned, u64);
>
> extern void generic_set_encrypted_ci_d_ops(struct dentry *dentry);
> +extern 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);
>
> static inline bool sb_has_encoding(const struct super_block *sb)
> {

--
Gabriel Krisman Bertazi