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Message-ID: <50d2afaa-fd7e-4772-ac84-24e8994bfba8@collabora.com>
Date: Mon, 19 Feb 2024 06:22:37 +0200
From: Eugen Hristev <eugen.hristev@...labora.com>
To: Gabriel Krisman Bertazi <krisman@...e.de>
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, Gabriel Krisman Bertazi <krisman@...labora.com>
Subject: Re: [PATCH v10 3/8] libfs: Introduce case-insensitive string
comparison helper
On 2/16/24 18:12, Gabriel Krisman Bertazi wrote:
> Eugen Hristev <eugen.hristev@...labora.com> writes:
>
>> From: Gabriel Krisman Bertazi <krisman@...labora.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.
>>
>> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
>> [eugen.hristev@...labora.com: rework to first test the exact match]
>> Signed-off-by: Eugen Hristev <eugen.hristev@...labora.com>
>> ---
>> fs/libfs.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++
>> include/linux/fs.h | 4 +++
>> 2 files changed, 84 insertions(+)
>>
>> diff --git a/fs/libfs.c b/fs/libfs.c
>> index bb18884ff20e..82871fa1b066 100644
>> --- a/fs/libfs.c
>> +++ b/fs/libfs.c
>> @@ -1773,6 +1773,86 @@ 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.
>> + *
>> + *
>
> Since this need a respin, mind dropping the extra empty line here?
>
>> + * 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;
>> +
>> + 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.
>> + */
>
> This paragraph doesn't really make sense here. It is originally from
> the d_compare hook, which can be called under RCU, but there is no RCU
> here. Also, here we are comparing the dirent with the
> name-under-lookup, name which is already safe.
>
>
>> + 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);
>
> Hmm, second thought on this. This will ignore errors from utf8_strncasecmp*,
> which CAN happen for the first time here, if the dirent itself is
> corrupted on disk (exactly why we have patch 6). Yes, ext4_match will drop the
> error, but we want to propagate it from here, such that the warning on
> patch 6 can trigger.
>
> This is why I did that match dance on the original submission. Sorry
> for suggesting it. We really want to get the error from utf8 and
> propagate it if it is negative. basically:
>
> res > 0: match
> res == 0: no match.
> res < 0: propagate error and let the caller handle it
In that case I will revert to the original v9 implementation and send a v11 to
handle that.
Eugen
>
>
>> + } 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);
>> + }
>> +
>> +out:
>> + kfree(decrypted_name.name);
>> + return res;
>> +}
>> +EXPORT_SYMBOL(generic_ci_match);
>> #endif
>>
>> #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)
>> {
>
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