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Key: CORE-5317
Type: Bug Bug
Status: Open Open
Priority: Minor Minor
Assignee: Unassigned
Reporter: Geoff Worboys
Votes: 0
Watchers: 3
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Firebird Core

Stack overflow in cvt.cpp with invalid DSC from UDF

Created: 23/Jul/16 04:56 PM   Updated: 26/Jul/16 01:06 PM
Component/s: UDF
Affects Version/s: 2.5.6
Fix Version/s: None

QA Status: No test


 Description  « Hide
I've marked this down as a UDF related issue because I don't imagine you should get invalid DSC from anywhere else.

If a UDF returns an invalid result "by descriptor" (an invalid DSC) then it is possible for CVT_Move to get called in an attempt to convert the return value. The conversion fails and calls CVT_conversion_error, which can result in a call to CVT_Move (trying to convert to the input to ASCII to give a useful message), but when the DSC is invalid that fails too and so we get infinite recursion and a stack overflow.

I was experimenting with changing the return dsc_type to 0 (unknown) because that apparently used to be a way to indicate an error to the server by causing a conversion error (according to a really old document by Claudio). But all I get now is a stack overflow.

Only reported as minor because, let's face it, the problem actually lies in the UDF. But it would be nice if the server would fail gracefully.

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Geoff Worboys added a comment - 26/Jul/16 01:06 PM
I have confirmed that this problem still exists in Firebird v3.0.0 (release version). It was only a very simple test - a UDF returning a paramdsc with a dsc_type of 0 - but it caused a stack overflow error.