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

Eugen Hristev
2024-06-05T10:49:01Z

On 6/4/24 22:17, Gabriel Krisman Bertazi wrote:
> 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;
>

Do you mean

return generic_ci_match(parent, fname->usr_fname,
&fname->cf_name, de->name,
de->name_len) > 0;

?

Because ext4_ci_compare was obsoleted with this series.

Thanks,
Eugen