Detect buffer underflow in get_th()

Hello everyone,

In src/backend/utils/adt/formatting.c:1516, there is a get_th() function utilized to return ST/ND/RD/TH suffixes for simple numbers.
Upon reviewing its behavior, it appears capable of receiving non-numeric inputs (this is verified by a check at formatting.c:1527).

Given that the function can accept non-numeric inputs,
it is plausible that it could also receive an empty input,
although a brief examination of its calls did not reveal any such instances.

Nevertheless, if the function were to receive an empty input of zero length,
a buffer underflow would occur when attempting to compute *(num + (len - 1)), as (len - 1) would result in a negative shift.
To mitigate this issue, I propose a patch incorporating the zero_length_character_string error code, as detailed in the attachment.

--
Best regards,
Alexander Kuznetsov

On 24.07.24 11:43, Alexander Kuznetsov wrote:
> Hello everyone,
>
> In src/backend/utils/adt/formatting.c:1516, there is a get_th() function
> utilized to return ST/ND/RD/TH suffixes for simple numbers.
> Upon reviewing its behavior, it appears capable of receiving non-numeric
> inputs (this is verified by a check at formatting.c:1527).
>
> Given that the function can accept non-numeric inputs,
> it is plausible that it could also receive an empty input,
> although a brief examination of its calls did not reveal any such
> instances.
>
> Nevertheless, if the function were to receive an empty input of zero
> length,
> a buffer underflow would occur when attempting to compute *(num + (len -
> 1)), as (len - 1) would result in a negative shift.
> To mitigate this issue, I propose a patch incorporating the
> zero_length_character_string error code, as detailed in the attachment.

If it can't happen in practice, maybe an assertion would be enough?

24.07.2024 18:39, Peter Eisentraut wrote:
> If it can't happen in practice, maybe an assertion would be enough?
>

In practice, the function should not receive non-numeric strings either; however, since there is an exception in place for such cases, I thought it would be good to add a check for zero-length input in a similar manner.

But of course it's open for discussion and team decision whether this should be addressed as an assertion or handled differently.

--
Best regards,
Alexander Kuznetsov

Hello,

is there anything else we can help with or discuss in order to apply this fix?

24.07.2024 18:53, Alexander Kuznetsov пишет:
>
> 24.07.2024 18:39, Peter Eisentraut wrote:
>> If it can't happen in practice, maybe an assertion would be enough?
>>
>
> In practice, the function should not receive non-numeric strings either; however, since there is an exception in place for such cases, I thought it would be good to add a check for zero-length input in a similar manner.
>
> But of course it's open for discussion and team decision whether this should be addressed as an assertion or handled differently.
>

--
Best regards,
Alexander Kuznetsov

Hello, ping?

24.09.2024 17:52, Alexander Kuznetsov wrote:
> Hello,
>
> is there anything else we can help with or discuss in order to apply this fix?
>
> 24.07.2024 18:53, Alexander Kuznetsov пишет:
>>
>> 24.07.2024 18:39, Peter Eisentraut wrote:
>>> If it can't happen in practice, maybe an assertion would be enough?
>>>
>>
>> In practice, the function should not receive non-numeric strings either; however, since there is an exception in place for such cases, I thought it would be good to add a check for zero-length input in a similar manner.
>>
>> But of course it's open for discussion and team decision whether this should be addressed as an assertion or handled differently.
>>
>

--
Best regards,
Alexander Kuznetsov

On 13.12.24 09:57, Alexander Kuznetsov wrote:
> Hello, ping?
>
> 24.09.2024 17:52, Alexander Kuznetsov wrote:
>> Hello,
>>
>> is there anything else we can help with or discuss in order to apply
>> this fix?
>>
>> 24.07.2024 18:53, Alexander Kuznetsov пишет:
>>>
>>> 24.07.2024 18:39, Peter Eisentraut wrote:
>>>> If it can't happen in practice, maybe an assertion would be enough?
>>>>
>>>
>>> In practice, the function should not receive non-numeric strings
>>> either; however, since there is an exception in place for such cases,
>>> I thought it would be good to add a check for zero-length input in a
>>> similar manner.
>>>
>>> But of course it's open for discussion and team decision whether this
>>> should be addressed as an assertion or handled differently.

After some further (internal) consultations, I have committed your fix
as an assertion. Thanks.