The Delphi Bug List

Entry No.
607

VCL - Data Access - DBTables
Invalid parameters passed to AnsiToNativeBuf and NativeToAnsiBuf can cause application to hang

1.02	2.01	3.0	3.01	3.02	4.0	4.01	4.02	4.03	5.0	5.01	6.0	6.01	6.02	Kylix 1.0
Absent	Absent	Absent	Absent	Absent	Absent	Absent	Absent	Absent	Absent	Exists	Fixed	Fixed	Fixed	N/A

Description

Reported by Anders Melander

The critical section used in AnsiToNativeBuf and NativeToAnsiBuf are not protected by a try..finally. This can cause an application to hang if one thread passes an invalid parameter to the function (e.g. a null pointer).

The following scenario demonstrates the bug:

Thread A calls AnsiToNativeBuf with null as either Source or Dest parameter.
AnsiToNativeBuf locks the critical section and then calls DbiAnsiToNative which throws an Access Violation.
Thread B calls AnsiToNativeBuf.
AnsiToNativeBuf attempts to lock the critical section but is blocked because thread A never unlocked it.
Application (or at least the thread) is hung.

Solution / workaround

Apply the following modification to AnsiToNativeBuf in dbTables.pas (apply similar changes to NativeToAnsiBuf):

procedure AnsiToNativeBuf(Locale: TLocale; Source, Dest: PChar; Len: Integer);
var
  DataLoss: LongBool;
begin
  if Len > 0 then
    if Locale <> nil then
    begin
      EnterCriticalSection(CSAnsiToNative);
      try
        DbiAnsiToNative(Locale, Dest, Source, Len, DataLoss);
      finally
        LeaveCriticalSection(CSAnsiToNative);
      end;
    end else
      CharToOemBuff(Source, Dest, Len);
end;

User-contributed comments

Anders Melander
19 Jun 2001 10:33 AM GMT

This problem has been fixed in Delphi 6.

Latest update of this entry: 2001-06-19

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