[ID 20001030.001] 5.7.0-7489: Null-Pointer reference in mg.c

Hi,

I ran into a segmentation violation caused by a NULL-pointer
reference in mg.c when I tried to display my procedures environment
using the debuggers 'X' command.
The stack trace showed:

    S_magic_methcall ---- SEGV within PUSHs(SvTIED_obj(sv, mg));
    S_magic_methpack
    Perl_magic_existspack
    Perl_av_exists
 
I had a closer look at the code and figured out, that this NULL-
pointer was cased by a failed mg_find in av.c line 800. This 
function call return '0' and passed this unchecked to the mg-
functions.


I've fixed this as follows:

diff -c av.c.FCS av.c
*** av.c.FCS    Mon Oct 30 14:13:05 2000
--- av.c        Mon Oct 30 14:14:33 2000
***************
*** 795,804 ****
      }
      if (SvRMAGICAL(av)) {
        if (mg_find((SV*)av,'P') || mg_find((SV*)av,'D')) {
            SV *sv = sv_newmortal();
            mg_copy((SV*)av, sv, 0, key);
!           magic_existspack(sv, mg_find(sv, 'p'));
!           return SvTRUE(sv);
        }
      }
      if (key <= AvFILLp(av) && AvARRAY(av)[key] != &PL_sv_undef
--- 795,808 ----
      }
      if (SvRMAGICAL(av)) {
        if (mg_find((SV*)av,'P') || mg_find((SV*)av,'D')) {
+           MAGIC *mg;
            SV *sv = sv_newmortal();
            mg_copy((SV*)av, sv, 0, key);
!           mg = mg_find(sv, 'p');
!           if( mg) {
!               magic_existspack(sv,mg);
!               return SvTRUE(sv);
!           }
        }
      }
      if (key <= AvFILLp(av) && AvARRAY(av)[key] != &PL_sv_undef


Hope this is sufficient ...

Regards
-- Jens

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• [ID 20001030.001] 5.7.0-7489: Null-Pointer reference in mg.c by Jens Hamisch
• Re: [ID 20001030.001] 5.7.0-7489: Null-Pointer reference in mg.c by Jarkko Hietaniemi