[Bug 2032667] Re: stack space full (SEGFAULT) when accessing %hash with undefined $var (use warnings)

[Niko Tyni]

On Tue, Aug 22, 2023 at 02:28:18PM -0000, Walter wrote:
 
> Accessing a hash entry with an undefined variable as key causes infinite
> recursion and running out of stack space. This only happens when '-w'
> ("use warnings;") is enabled.

This is https://github.com/Perl/perl5/issues/19147 , broken around 5.33.1
and fixed around 5.35.5 with 

https://github.com/Perl/perl5/commit/23cca2d1f4544cb47f1124d98c308ce1f31f09a6

Hope this helps somebody fix this in Ubuntu. Debian is not affected as we
never shipped 5.34 in a stable release.
-- 
Niko Tyni   ntyni at debian.org

** Bug watch added: github.com/Perl/perl5/issues #19147
   https://github.com/Perl/perl5/issues/19147

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https://bugs.launchpad.net/bugs/2032667

Title:
  stack space full (SEGFAULT) when accessing %hash with undefined $var
  (use warnings)

Status in perl package in Ubuntu:
  New

Bug description:
  Accessing a hash entry with an undefined variable as key causes
  infinite recursion and running out of stack space. This only happens
  when '-w' ("use warnings;") is enabled.

  Steps to reproduce:

    $ perl -e 'my %hash = (); int($hash{$undefined_var})'
    (no crash)

    $ perl -we 'my %hash = (); int($hash{$undefined_var})'
    Useless use of int in void context at -e line 1.
    Name "main::undefined_var" used only once: possible typo at -e line 1.
    Use of uninitialized value $undefined_var in hash element at -e line 1.
    Segmentation fault
   
  Version: perl-base (5.34.0-3ubuntu1.2) on Jammy

  Backtrace (after installing perl-debug):

    Program received signal SIGSEGV, Segmentation fault.
    0x0000555555652d1d in Perl_hv_common (my_perl=0x5555558fa2a0, hv=0x5555559292b8, keysv=0x555555929318, key=0x0, klen=0, flags=0, action=0, val=0x0, hash=0) at /build/perl-Jo9ODt/perl-5.34.0/build-static/hv.c:350
    350	in /build/perl-Jo9ODt/perl-5.34.0/build-static/hv.c
    (gdb) bt 10
    #0  0x0000555555652d1d in Perl_hv_common (
        my_perl=0x5555558fa2a0, hv=0x5555559292b8, 
        keysv=0x555555929318, key=0x0, klen=0, flags=0, 
        action=0, val=0x0, hash=0)
        at /build/perl-Jo9ODt/perl-5.34.0/build-static/hv.c:350
    #1  0x0000555555684afc in S_find_uninit_var (
        my_perl=0x5555558fa2a0, obase=<optimized out>, 
        uninit_sv=<optimized out>, match=<optimized out>, 
        desc_p=<optimized out>)
        at /build/perl-Jo9ODt/perl-5.34.0/build-static/sv.c:16785
    #2  0x0000555555684ce4 in Perl_report_uninit (
        my_perl=0x5555558fa2a0, uninit_sv=0x555555929318)
        at /build/perl-Jo9ODt/perl-5.34.0/build-static/sv.c:17051
    #3  0x000055555566771d in Perl_sv_2pv_flags (
        my_perl=0x5555558fa2a0, sv=0x555555929318, 
        lp=0x7fffff7ff1c8, flags=<optimized out>)
        at /build/perl-Jo9ODt/perl-5.34.0/build-static/sv.c:3243
    #4  0x0000555555652fd5 in Perl_hv_common (
        my_perl=0x5555558fa2a0, hv=0x5555559292b8, 
        keysv=0x555555929318, key=0x0, klen=<optimized out>, 
        flags=<optimized out>, action=0, val=0x0, 
        hash=<optimized out>)
        at /build/perl-Jo9ODt/perl-5.34.0/build-static/hv.c:396
    #5  0x0000555555684afc in S_find_uninit_var (
        my_perl=0x5555558fa2a0, obase=<optimized out>, 
        uninit_sv=<optimized out>, match=<optimized out>, 
        desc_p=<optimized out>)
        at /build/perl-Jo9ODt/perl-5.34.0/build-static/sv.c:16785
    #6  0x0000555555684ce4 in Perl_report_uninit (
        my_perl=0x5555558fa2a0, uninit_sv=0x555555929318)
        at /build/perl-Jo9ODt/perl-5.34.0/build-static/sv.c:17051
    #7  0x000055555566771d in Perl_sv_2pv_flags (
        my_perl=0x5555558fa2a0, sv=0x555555929318, 
        lp=0x7fffff7ff3b8, flags=<optimized out>)
        at /build/perl-Jo9ODt/perl-5.34.0/build-static/sv.c:3243
    #8  0x0000555555652fd5 in Perl_hv_common (
        my_perl=0x5555558fa2a0, hv=0x5555559292b8, 
        keysv=0x555555929318, key=0x0, klen=<optimized out>, 
        flags=<optimized out>, action=0, val=0x0, 
        hash=<optimized out>)
        at /build/perl-Jo9ODt/perl-5.34.0/build-static/hv.c:396
    #9  0x0000555555684afc in S_find_uninit_var (
        my_perl=0x5555558fa2a0, obase=<optimized out>, 
        uninit_sv=<optimized out>, match=<optimized out>, 
        desc_p=<optimized out>)
        at /build/perl-Jo9ODt/perl-5.34.0/build-static/sv.c:16785
    (More stack frames follow...)

  Long backtrace:

    #0  0x0000555555652d1d in Perl_hv_common (my_perl=..., hv=..
    #1  0x0000555555684afc in S_find_uninit_var (my_perl=..., ob
    #2  0x0000555555684ce4 in Perl_report_uninit (my_perl=..., u
    #3  0x000055555566771d in Perl_sv_2pv_flags (my_perl=..., sv
    #4  0x0000555555652fd5 in Perl_hv_common (my_perl=..., hv=..
    #5  0x0000555555684afc in S_find_uninit_var (my_perl=..., ob
    #6  0x0000555555684ce4 in Perl_report_uninit (my_perl=..., u
    #7  0x000055555566771d in Perl_sv_2pv_flags (my_perl=..., sv
    #8  0x0000555555652fd5 in Perl_hv_common (my_perl=..., hv=..
    #9  0x0000555555684afc in S_find_uninit_var (my_perl=..., ob
    ...
    #67607 0x000055555566771d in Perl_sv_2pv_flags (my_perl=...,
    #67608 0x0000555555652fd5 in Perl_hv_common (my_perl=..., hv
    #67609 0x0000555555684afc in S_find_uninit_var (my_perl=...,
    #67610 0x0000555555684ce4 in Perl_report_uninit (my_perl=...
    #67611 0x000055555566524a in Perl_sv_2iv_flags (my_perl=...,
    #67612 0x000055555568e21d in Perl_pp_int (my_perl=...)
    #67613 0x000055555564fac6 in Perl_runops_standard (my_perl=.
    #67614 0x00005555555c955c in S_run_body (oldscope=..., my_pe
    #67615 perl_run (my_perl=...)
    #67616 0x000055555559e977 in main (argc=..., argv=..., env=.

  Cheers!

  Walter Doekes
  OSSO B.V.

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