Re: [PATCH v17 4/7] ext4: Reuse generic_ci_match for ci comparisons

Gabriel Krisman Bertazi
2024-06-04T19:17:50Z

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

> From: Gabriel Krisman Bertazi <krisman@collabora.com>
>
> Instead of reimplementing ext4_match_ci, use the new libfs helper.
>
> It also adds a comment explaining why fname->cf_name.name must be
> checked prior to the encryption hash optimization, because that tripped
> me before.
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
> Signed-off-by: Eugen Hristev <eugen.hristev@collabora.com>
> Reviewed-by: Eric Biggers <ebiggers@google.com>
> ---
> fs/ext4/namei.c | 91 +++++++++++++++----------------------------------
> 1 file changed, 27 insertions(+), 64 deletions(-)
>
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index ec4c9bfc1057..20668741a23c 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -1390,58 +1390,6 @@ static void dx_insert_block(struct dx_frame *frame, u32 hash, ext4_lblk_t block)
> }
>
> #if IS_ENABLED(CONFIG_UNICODE)
> -/*
> - * Test whether a case-insensitive directory entry matches the filename
> - * being searched for. If quick is set, assume the name being looked up
> - * is already in the casefolded form.
> - *
> - * Returns: 0 if the directory entry matches, more than 0 if it
> - * doesn't match or less than zero on error.
> - */
> -static int ext4_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)) {
> - const struct fscrypt_str encrypted_name =
> - FSTR_INIT(de_name, de_name_len);
> -
> - decrypted_name.name = kmalloc(de_name_len, GFP_KERNEL);
> - if (!decrypted_name.name)
> - return -ENOMEM;
> - ret = fscrypt_fname_disk_to_usr(parent, 0, 0, &encrypted_name,
> - &decrypted_name);
> - if (ret < 0)
> - goto out;
> - entry.name = decrypted_name.name;
> - entry.len = decrypted_name.len;
> - }
> -
> - 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.
> - */
> - if (sb_has_strict_encoding(sb))
> - ret = -EINVAL;
> - else if (name->len != entry.len)
> - ret = 1;
> - else
> - ret = !!memcmp(name->name, entry.name, entry.len);
> - }
> -out:
> - kfree(decrypted_name.name);
> - return ret;
> -}
> -
> int ext4_fname_setup_ci_filename(struct inode *dir, const struct qstr *iname,
> struct ext4_filename *name)
> {
> @@ -1503,20 +1451,35 @@ static bool ext4_match(struct inode *parent,
> #if IS_ENABLED(CONFIG_UNICODE)
> if (IS_CASEFOLDED(parent) &&
> (!IS_ENCRYPTED(parent) || fscrypt_has_encryption_key(parent))) {
> - if (fname->cf_name.name) {
> - if (IS_ENCRYPTED(parent)) {
> - if (fname->hinfo.hash != EXT4_DIRENT_HASH(de) ||
> - fname->hinfo.minor_hash !=
> - EXT4_DIRENT_MINOR_HASH(de)) {
> + int ret;
>
> - return false;
> - }
> - }
> - return !ext4_ci_compare(parent, &fname->cf_name,
> - de->name, de->name_len, true);
> + /*
> + * Just checking IS_ENCRYPTED(parent) below is not
> + * sufficient to decide whether one can use the hash for
> + * skipping the string comparison, because the key might
> + * have been added right after
> + * ext4_fname_setup_ci_filename(). In this case, a hash
> + * mismatch will be a false negative. Therefore, make
> + * sure cf_name was properly initialized before
> + * considering the calculated hash.
> + */
> + if (IS_ENCRYPTED(parent) && fname->cf_name.name &&
> + (fname->hinfo.hash != EXT4_DIRENT_HASH(de) ||
> + fname->hinfo.minor_hash != EXT4_DIRENT_MINOR_HASH(de)))
> + return false;
> +
> + ret = generic_ci_match(parent, fname->usr_fname,
> + &fname->cf_name, de->name,
> + de->name_len);
> + if (ret < 0) {
> + /*
> + * Treat comparison errors as not a match. The
> + * only case where it happens is on a disk
> + * corruption or ENOMEM.
> + */
> + return false;
> }
> - return !ext4_ci_compare(parent, fname->usr_fname, de->name,
> - de->name_len, false);

With the changes to patch 3 in this iteration, This could become:

/*
* Treat comparison errors as not a match. The
* only case where it happens is disk corruption
* or ENOMEM.
*/
return ext4_ci_compare(parent, fname->usr_fname, de->name,
de->name_len, false) > 0;

--
Gabriel Krisman Bertazi