Eugen Hristev <eugen.hris...@collabora.com> writes:
> From: Gabriel Krisman Bertazi <kris...@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.
>
> Reviewed-by: Eric Biggers <ebigg...@google.com>
> Signed-off-by: Gabriel Krisman Bertazi <kris...@collabora.com>
> Signed-off-by: Eugen Hristev <eugen.hris...@collabora.com>
Hi Eugen,
Thanks for picking this up. Please, CC me in future versions.
> ---
> fs/libfs.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 4 +++
> 2 files changed, 72 insertions(+)
>
> diff --git a/fs/libfs.c b/fs/libfs.c
> index bb18884ff20e..f80cb982ac89 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -1773,6 +1773,74 @@ 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.
> + * @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.
Can we add a note that this is a filesystem helper for comparison with
directory entries, and VFS' ->d_compare should use generic_ci_d_compare.
> + *
> + * 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 = false;
I know I originally wrote it this way, but match is an integer, so
let's use integers instead of false/true.
> +
> + 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;
> + }
> +
> + if (folded_name->name)
> + res = utf8_strncasecmp_folded(um, folded_name, &dirent);
> + else
> + res = utf8_strncasecmp(um, name, &dirent);
Similar to
https://git.kernel.org/pub/scm/linux/kernel/git/krisman/unicode.git/commit/?h=for-next&id=367122c529f35b4655acbe33c0cc4d6d3b32ba71
We should be checking for an exact-match first to avoid the utf8
comparison cost unnecessarily. The only problem is that we need to
ensure we fail for an invalid utf-8 de_name in "strict mode".
Fortunately, if folded_name->name exists, we know the name-under-lookup
was validated when initialized, so an exact-match of de_name must also
be valid. If folded_name is NULL, though, we might either have an
invalid utf-8 dentry-under-lookup or the allocation itself failed, so we
need to utf8_validate it.
Honestly, I don't care much about this !folded_name->name case, since
utf8_strncasecmp will do the right thing and an invalid utf8 on
case-insensitive directories should be an exception, not the norm. but
the code might get simpler if we do both:
(untested)
if (folded_name->name) {
if (dirent.len == folded_name->len &&
!memcmp(folded_name->name, dirent.name, dirent.len)) {
res = 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))) {
res = 1;
goto out;
}
res = utf8_strncasecmp(um, name, &dirent);
}
> +
> + if (!res)
> + match = true;
> + else if (res < 0 && !sb_has_strict_encoding(sb)) {
> + /*
> + * In non-strict mode, fallback to a byte comparison if
> + * the names have invalid characters.
> + */
> + res = 0;
> + match = ((name->len == dirent.len) &&
> + !memcmp(name->name, dirent.name, dirent.len));
> + }
This goes away entirely.
> +
> +out:
> + kfree(decrypted_name.name);
> + return (res >= 0) ? match : res;
and this becomes:
return res;
--
Gabriel Krisman Bertazi
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