Assert fail in sv.c with no further symptoms: e t''/$0{\0}

[p5pRT]

Migrated from rt.perl.org#128189 (status was 'resolved')

Searchable as RT128189$

[p5pRT]

From @dcollinsn

I have compiled bleadperl with the afl-gcc compiler using​:

./Configure -Dusedevel -Dprefix='/usr/local/perl-afl' -Dcc='ccache afl-gcc' -Uuselongdouble -Duse64bitall -Doptimize=-g -Uversiononly -Uman1dir -Uman3dir -Dusequadmath -DDEBUGGING -des
AFL_HARDEN=1 make && make test

And then fuzzed the resulting binary using​:

AFL_NO_VAR_CHECK=1 afl-fuzz -i in -o out bin/perl -t -W @​@​

After reducing testcases using `afl-tmin` and performing additional minimization by hand, I have located the following testcase that triggers an assert fail in debugging builds of the perl interpreter. The testcase is the file below. On normal builds, this exits with the expected error. On debug builds with -W, this returns an assert fail.

dcollins@​nightshade64​:~$ perl/miniperl -W -e 'e t""/$0{\0}'
Use of uninitialized value $0{"\200\350{\2\0\0\0\0\1\0\0\0\1\21"...} in division (/) at -e line 1.
Argument "" isn't numeric in division (/) at -e line 1.
Illegal division by zero at -e line 1.
dcollins@​nightshade64​:~$ perldebug/miniperl -W -e 'e t""/$0{\0}'
miniperl​: sv.c​:15687​: Perl_varname​: Assertion `PL_valid_types_PVX[((svtype)((_svcur)->sv_flags & 0xff)) & 0xf] || ((svtype)((_svcur)->sv_flags & 0xff)) == SVt_REGEXP' failed.
Aborted

Debugging tool output is below. A git bisect was attempted, but this persists as far back as 5.14.0, which is also as far back as I'm able to compile right now.

**GDB**

dcollins@​nightshade64​:~$ gdb --args perldebug/miniperl -W -e 'e t""/$0{\0}'
GNU gdb (GDB) 7.10
Copyright (C) 2015 Free Software Foundation, Inc.
License GPLv3+​: GNU GPL version 3 or later <http​://gnu.org/licenses/gpl.html>
This is free software​: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-unknown-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see​:
<http​://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at​:
<http​://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from perldebug/miniperl...done.
(gdb) run
Starting program​: /home/dcollins/perldebug/miniperl -W -e e\ t\"\"/\$0\{\\0\}
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
miniperl​: sv.c​:15687​: Perl_varname​: Assertion `PL_valid_types_PVX[((svtype)((_svcur)->sv_flags & 0xff)) & 0xf] || ((svtype)((_svcur)->sv_flags & 0xff)) == SVt_REGEXP' failed.

Program received signal SIGABRT, Aborted.
0x00007ffff6cf9478 in raise () from /lib/x86_64-linux-gnu/libc.so.6
(gdb) bt
#0 0x00007ffff6cf9478 in raise () from /lib/x86_64-linux-gnu/libc.so.6
#1 0x00007ffff6cfa8fa in abort () from /lib/x86_64-linux-gnu/libc.so.6
#2 0x00007ffff6cf23a7 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#3 0x00007ffff6cf2452 in __assert_fail () from /lib/x86_64-linux-gnu/libc.so.6
#4 0x00000000005fee9c in Perl_varname (gv=0xa96868, gvtype=37 '%', targ=0, keyname=0xa96bb0, aindex=0, subscript_type=3) at sv.c​:15686
#5 0x000000000060038c in S_find_uninit_var (obase=0xa9fd08, uninit_sv=0xa7e840 <PL_sv_undef>, match=false, desc_p=0x7fffffffdf78) at sv.c​:15926
#6 0x00000000006018dd in S_find_uninit_var (obase=0xa9fcc0, uninit_sv=0xa7e840 <PL_sv_undef>, match=false, desc_p=0x7fffffffdf78) at sv.c​:16356
#7 0x0000000000601a80 in Perl_report_uninit (uninit_sv=0xa7e840 <PL_sv_undef>) at sv.c​:16390
#8 0x00000000005b50a5 in Perl_sv_2nv_flags (sv=0xa7e840 <PL_sv_undef>, flags=0) at sv.c​:2645
#9 0x000000000060f407 in Perl_pp_divide () at pp.c​:1627
#10 0x000000000053f5f1 in Perl_runops_debug () at dump.c​:2239
#11 0x00000000004481a1 in S_run_body (oldscope=1) at perl.c​:2517
#12 0x00000000004477cc in perl_run (my_perl=0xa80010) at perl.c​:2440
#13 0x000000000072889a in main (argc=4, argv=0x7fffffffe618, env=0x7fffffffe640) at miniperlmain.c​:122
(gdb) f 4
#4 0x00000000005fee9c in Perl_varname (gv=0xa96868, gvtype=37 '%', targ=0, keyname=0xa96bb0, aindex=0, subscript_type=3) at sv.c​:15686
15686 pv_pretty(sv, SvPVX_const(keyname), SvCUR(keyname), 32, NULL, NULL,
(gdb) info locals
_svcur = 0xa96bb0
sv = 0xa963a0
name = 0xa82178
__PRETTY_FUNCTION__ = "Perl_varname"
(gdb) q

**PERL -V**

dcollins@​nightshade64​:~$ perl/perl -V
Summary of my perl5 (revision 5 version 25 subversion 1) configuration​:
  Commit id​: 9e17953
  Platform​:
  osname=linux, osvers=4.5.0-2-amd64, archname=x86_64-linux-ld
  uname='linux nightshade64 4.5.0-2-amd64 #1 smp debian 4.5.3-2 (2016-05-08) x86_64 gnulinux '
  config_args='-Dusedevel -Dprefix=/usr/local/perl-afl -Dcc=ccache afl-gcc -Duselongdouble -Duse64bitall -Doptimize=-g -Uversiononly -Uman1dir -Uman3dir -DDEBUGGING -DDEBUG_LEAKING_SCALARS -des'
  hint=recommended, useposix=true, d_sigaction=define
  useithreads=undef, usemultiplicity=undef
  use64bitint=define, use64bitall=define, uselongdouble=define
  usemymalloc=n, bincompat5005=undef
  Compiler​:
  cc='ccache afl-gcc', ccflags ='-fwrapv -DDEBUGGING -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
  optimize='-g',
  cppflags='-fwrapv -DDEBUGGING -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
  ccversion='', gccversion='6.1.0', gccosandvers=''
  intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678, doublekind=3
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16, longdblkind=3
  ivtype='long', ivsize=8, nvtype='long double', nvsize=16, Off_t='off_t', lseeksize=8
  alignbytes=16, prototype=define
  Linker and Libraries​:
  ld='ccache afl-gcc', ldflags =' -fstack-protector-strong -L/usr/local/lib'
  libpth=/usr/local/lib /usr/local/lib/gcc/x86_64-pc-linux-gnu/6.1.0/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib
  libs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
  perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
  libc=libc-2.22.so, so=so, useshrplib=false, libperl=libperl.a
  gnulibc_version='2.22'
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
  cccdlflags='-fPIC', lddlflags='-shared -g -L/usr/local/lib -fstack-protector-strong'

Characteristics of this binary (from libperl)​:
  Compile-time options​: HAS_TIMES PERLIO_LAYERS PERL_COPY_ON_WRITE
  PERL_DONT_CREATE_GVSV
  PERL_HASH_FUNC_ONE_AT_A_TIME_HARD PERL_MALLOC_WRAP
  PERL_OP_PARENT PERL_PRESERVE_IVUV PERL_USE_DEVEL
  USE_64_BIT_ALL USE_64_BIT_INT USE_LARGE_FILES
  USE_LOCALE USE_LOCALE_COLLATE USE_LOCALE_CTYPE
  USE_LOCALE_NUMERIC USE_LOCALE_TIME USE_LONG_DOUBLE
  USE_PERLIO USE_PERL_ATOF
  Built under linux
  Compiled at May 17 2016 20​:01​:23
  @​INC​:
  /usr/local/perl-afl/lib/site_perl/5.25.1/x86_64-linux-ld
  /usr/local/perl-afl/lib/site_perl/5.25.1
  /usr/local/perl-afl/lib/5.25.1/x86_64-linux-ld
  /usr/local/perl-afl/lib/5.25.1
  /usr/local/perl-afl/lib/site_perl/5.24.0
  /usr/local/perl-afl/lib/site_perl
  .

[p5pRT]

From @dcollinsn

The slightly shorter testcase​:

perl -W -e 'e f/$0{\0}/'

also shows this error

[p5pRT]

From @dcollinsn

I really should finish looking through my queue before posting. Best testcase is the 8-character file​:

miniperl -W -e '0/$0{\0}'

[p5pRT]

From @cpansprout

On Thu May 19 14​:53​:18 2016, dcollinsn@​gmail.com wrote​:

The slightly shorter testcase​:

perl -W -e 'e f/$0{\0}/'

also shows this error

Shorter​:

perl -we '"$0{\0}"'
perl -we '/$0{\0}/'

Any uninitialized warning that tries to mention $0{\0} will trigger it.

--

Father Chrysostomos

[p5pRT]

The RT System itself - Status changed from 'new' to 'open'

[p5pRT]

From @cpansprout

On Thu May 19 15​:02​:05 2016, sprout wrote​:

On Thu May 19 14​:53​:18 2016, dcollinsn@​gmail.com wrote​:

The slightly shorter testcase​:

perl -W -e 'e f/$0{\0}/'

also shows this error

Shorter​:

perl -we '"$0{\0}"'
perl -we '/$0{\0}/'

Any uninitialized warning that tries to mention $0{\0} will trigger it.

It appears that the subscript has to be an OP_CONST, because qr// doesn’t trigger it.

A bisect points to​:

commit 04698ff
Author​: Father Chrysostomos <sprout@​cpan.org>
Date​: Sat Nov 27 06​:22​:24 2010 -0800

  [perl #79178] STORE/FETCH of tie()d hash get stringified key

but that is a red herring. It fixed another bug, exposing this one.

Here is a similar bug with array indices. There is no crash here, but the number in the subscript is bogus​:

$ ./miniperl -we '"$0[\0]"'
Useless use of string in void context at -e line 1.
Use of reference "SCALAR(0x7fad6882fcf0)" as array index at -e line 1.
Use of uninitialized value $0[1753414896] in string at -e line 1.
$ perl -le 'print 0x7fad6882fcf0'
140382759484656

I would expect the output of the latter command to match the subscript in the uninit warning.

--

Father Chrysostomos

[p5pRT]

From zefram@fysh.org

Father Chrysostomos via RT wrote​:

Use of reference "SCALAR(0x7fad6882fcf0)" as array index at -e line 1.
Use of uninitialized value $0[1753414896] in string at -e line 1.

$ perl -le 'printf "%x\n", 1753414896'
6882fcf0

The index has been truncated to 32 bits, that's all.

-zefram

[p5pRT]

From @cpansprout

On Thu May 19 15​:33​:41 2016, zefram@​fysh.org wrote​:

Father Chrysostomos via RT wrote​:

Use of reference "SCALAR(0x7fad6882fcf0)" as array index at -e line 1.
Use of uninitialized value $0[1753414896] in string at -e line 1.

$ perl -le 'printf "%x\n", 1753414896'
6882fcf0

The index has been truncated to 32 bits, that's all.

I thought it might be that. I was too lazy to check. That itself is also a bug, though.

--

Father Chrysostomos

[p5pRT]

From @iabyn

On Thu, May 19, 2016 at 05​:18​:31PM -0700, Father Chrysostomos via RT wrote​:

On Thu May 19 15​:33​:41 2016, zefram@​fysh.org wrote​:

Father Chrysostomos via RT wrote​:

Use of reference "SCALAR(0x7fad6882fcf0)" as array index at -e line 1.
Use of uninitialized value $0[1753414896] in string at -e line 1.

$ perl -le 'printf "%x\n", 1753414896'
6882fcf0

The index has been truncated to 32 bits, that's all.

I thought it might be that. I was too lazy to check. That itself is also a bug, though.

The original issue is now fixed with v5.25.2-15-g55b6481.
I'm not going to address the 32-bitness of the AV API here.

--
Dave's first rule of Opera​:
If something needs saying, say it​: don't warble it.

[p5pRT]

@iabyn - Status changed from 'open' to 'resolved'

[p5pRT]

From @cpansprout

On Tue Jun 21 07​:29​:25 2016, davem wrote​:

I'm not going to address the 32-bitness of the AV API here.

The AV API was changed to support 64-bit indices some time ago (e.g. v5.19.3-99-gc70927a), but report_uninit_var got left behind.

I have fixed it in commit 1b3df0e.

--

Father Chrysostomos