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SubjectRe: [RESEND PATCH v2] hfsplus: prevent negative dentries when casefolded
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> On Jul 19, 2021, at 2:03 AM, Chung-Chiang Cheng <cccheng@synology.com> wrote:
>
> This function revalidates dentries without blocking and storing to the
> dentry. As the document mentioned [1], I think it's safe in rcu-walk
> mode. I also found jfs_ci_revalidate() takes the same approach.
>
> d_revalidate may be called in rcu-walk mode (flags & LOOKUP_RCU).
> If in rcu-walk mode, the filesystem must revalidate the dentry without
> blocking or storing to the dentry, d_parent and d_inode should not be
> used without care (because they can change and, in d_inode case, even
> become NULL under us
>
>
> [1] https://www.kernel.org/doc/Documentation/filesystems/vfs.txt
>


I am still not convinced by the explanation.

>> This patch takes the same approach to drop negative dentires as vfat does.

You mentioned that you follows by vfat approach. But this code contains this code, as far as I can see. How could you prove that we will not introduce some weird bug here? What if code of this function will be changed in the future? I suppose that missing of this code could be the way to introduce some bug, anyway.

>> touch aaa
>> rm aaa
>> touch AAA

By the way, have you tested other possible combinations? I mean (1) ‘aaa’ -> ‘AAA’, (2) ‘AAA’ -> ‘aaa’, (3) ‘aaa’ -> ‘aaa’, (4) ‘AAA’ -> ‘AAA’. Could you please add in the comment that it was tested? Could we create the file in case-insensitive mode and, then, try to delete in case-sensitive and vise versa? Do we define this flag during volume creation? Can we change the flag by volume tuning?

Thanks,
Slava.


> Thanks,
> C.C.Cheng
>
>>> +
>>> +int hfsplus_revalidate_dentry(struct dentry *dentry, unsigned int flags)
>>> +{
>> What’s about this code?
>>
>> If (flags & LOOKUP_RCU)
>> return -ECHILD;
>>
>> Do we really need to miss it here?
>>
>> Thanks,
>> Slava.
>>
>>
>>> + /*
>>> + * dentries are always valid when disabling casefold.
>>> + */
>>> + if (!test_bit(HFSPLUS_SB_CASEFOLD, &HFSPLUS_SB(dentry->d_sb)->flags))
>>> + return 1;
>>> +
>>> + /*
>>> + * Positive dentries are valid when enabling casefold.
>>> + *
>>> + * Note, rename() to existing directory entry will have ->d_inode, and
>>> + * will use existing name which isn't specified name by user.
>>> + *
>>> + * We may be able to drop this positive dentry here. But dropping
>>> + * positive dentry isn't good idea. So it's unsupported like
>>> + * rename("filename", "FILENAME") for now.
>>> + */
>>> + if (d_really_is_positive(dentry))
>>> + return 1;
>>> +
>>> + /*
>>> + * Drop the negative dentry, in order to make sure to use the case
>>> + * sensitive name which is specified by user if this is for creation.
>>> + */
>>> + if (flags & (LOOKUP_CREATE | LOOKUP_RENAME_TARGET))
>>> + return 0;
>>> +
>>> + return 1;
>>> +}
>>> --
>>> 2.25.1
>>>

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