libc/regex: r302824 added invalid check breaking collating ranges

[Yuri Pankov]

On Wed, Jan 24, 2018 at 07:17:27AM +0300, Yuri Pankov wrote:
> On Tue, Jan 23, 2018 at 01:22:04PM -0600, Kyle Evans wrote:
>> On Tue, Jan 23, 2018 at 1:10 PM, Yuri Pankov <yuripv at icloud.com> wrote:
>>> On Tue, Jan 23, 2018 at 08:10:32AM -0600, Kyle Evans wrote:
>>>>
>>>> On Mon, Jan 22, 2018 at 11:36 PM, Yuri Pankov <yuripv at icloud.com> wrote:
>>>>>
>>>>> On Tue, Jan 23, 2018 at 03:53:19AM +0300, Yuri Pankov wrote:
>>>>>>
>>>>>>
>>>>>> (CCing Kyle as he's working on regex at the moment and not because he
>>>>>> broke something)
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> r302284 added an invalid check which breaks collating ranges:
>>>>>>
>>>>>> -if (table->__collate_load_error) {
>>>>>> -    (void)REQUIRE((uch)start <= (uch)finish, REG_ERANGE);
>>>>>> +if (table->__collate_load_error || MB_CUR_MAX > 1) {
>>>>>> +    (void)REQUIRE(start <= finish, REG_ERANGE);
>>>>>>
>>>>>> The "MB_CUR_MAX > 1" is wrong, we should be doing proper comparison
>>>>>> according to current locale's collation and not simply comparing the
>>>>>> wchar_t values.
>>>>>
>>>>>
>>>>>
>>>>> After re-reading the specification I now see that what looked like a bug
>>>>> is
>>>>> actually an implementation choice, though the one that needs to be
>>>>> documentated.  I'll update the man page if anyone is willing to review
>>>>> (and
>>>>> commit) the changes.
>>>>
>>>>
>>>> Can you point to the section of specification that indicates this is
>>>> OK behavior? It doesn't seem desirable, but I see that GNU systems
>>>> will operate in the same manner that we do now.
>>>
>>>
>>> Here --
>>> http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html:
>>> ------------------------------------------------------------------------
>>> In the POSIX locale, a range expression represents the set of collating
>>> elements that fall between two elements in the collation sequence,
>>> inclusive. In other locales, a range expression has unspecified behavior:
>>> strictly conforming applications shall not rely on whether the range
>>> expression is valid, or on the set of collating elements matched.
>>> ------------------------------------------------------------------------
>>>
>>
>> Thanks- our current behavior seems reasonable in that context.
>>
>>> I've tried to "fix" what I was seeing as well, and yes, everything outside
>>> of ASCII is ugly, e.g. Cyrillic 'а-я' would match much more than you could
>>> expect if you are doing lookups based on collation order (capital chars and
>>> a lot of other symbols).
>>>
>>> So what we have currently looks the least evil to me:
>>>
>>> - non-collating ASCII lookups for any locale -- looking at the log for
>>>     regcomp.c there was an attempt to "fix" this, but it was reverted as
>>>     a lot of existing code relies on this;
>>> - non-collating multi-byte locale lookups -- they will work for almost
>>>     all   cases, and where they don't, well POSIX says it's undefined :D
>>> - collating single-byte locale lookups for outside of ASCII range --
>>>     they make sense as collation order there doesn't seem to mix
>>>     small/caps/other characters together.
>>>
>>> What I think we need to do is document this as implementation choice in the
>>> code and regex(3) "IMPLEMENTATION NOTES" so that another poor soul doesn't
>>> come trying to fix it as I did :-)
>>
>> I agree with your assessment- such a patch would be welcomed,
>> especially before I go and revise a bunch of this for clarification in
>> a future libregex world.
> 
> Actually, it's broken even more than I thought:
> 
> $ echo 'TEST' | LC_ALL=en_US.ISO8859-1 grep '[a-z]'
> TEST
> 
> That's a result of using collation lookup for singlebyte locales.  Now I
> just think that using collations for range expressions in *any* locale
> is just plain wrong.
> 
> Another side effect of all this "sometimes non-collating" nonsense is
> inability to deal with multibyte characters whose corresponding wide
> character is in 128-255 range -- try adding 'µ' (\302\265, U+00B5) to
> the pattern and observe a nice ~1GB core from grep after endless loop in
> regcomp().  This is due to NC (I guess meaning "non-collating") being
> defined as (CHAR_MAX - CHAR_MIN + 1) which is 256.

Oh, and the lookup should be case-insensitive above to reproduce the issue.

> To sum the above, how about we drop the "non-collating" notion, and just
> use binary wide character comparison everywhere?