sv.c:6545: void Perl_sv_clear(SV *const): Assertion `SvTYPE(sv) != (svtype)SVTYPEMASK' failed

[p5pRT]

Migrated from rt.perl.org#130667 (status was 'open')

Searchable as RT130667$

[p5pRT]

From @dur-randir

Created by @dur-randir

While fuzzing perl v5.25.9-35-g32207c637b built with afl and run
under libdislocator, I found the following program

a{%0=local$0,%0=0}

to cause an assertion failure on debugging builds and crash on regular builds.
This is a regression in blead, bisect points to

8b0c337 is the first bad commit
commit 8b0c337
Author​: David Mitchell <davem@​iabyn.com>
Date​: Wed Oct 5 10​:10​:56 2016 +0100

  Better optimise array and hash assignment

  [perl #127999] Slowdown in split + list assign

GDB info about the crash location​:

(gdb) bt
#0 __GI_raise (sig=sig@​entry=6) at ../sysdeps/unix/sysv/linux/raise.c​:58
#1 0x00007f96ae90f40a in __GI_abort () at abort.c​:89
#2 0x00007f96ae906e47 in __assert_fail_base (fmt=<optimized out>,
assertion=assertion@​entry=0x7f96b07d8530 "SvTYPE(sv) !=
(svtype)SVTYPEMASK",
  file=file@​entry=0x7f96b07d7196 "sv.c", line=line@​entry=6545,
function=function@​entry=0x7f96b07e5308 <__PRETTY_FUNCTION__.19252>
"Perl_sv_clear")
  at assert.c​:92
#3 0x00007f96ae906ef2 in __GI___assert_fail
(assertion=assertion@​entry=0x7f96b07d8530 "SvTYPE(sv) !=
(svtype)SVTYPEMASK",
  file=file@​entry=0x7f96b07d7196 "sv.c", line=line@​entry=6545,
function=function@​entry=0x7f96b07e5308 <__PRETTY_FUNCTION__.19252>
"Perl_sv_clear")
  at assert.c​:101
#4 0x00007f96b01a1c87 in Perl_sv_clear
(orig_sv=orig_sv@​entry=0x7f96b1d75510) at sv.c​:6545
#5 0x00007f96b01a1f3c in Perl_sv_free2 (sv=0x7f96b1d75510,
rc=<optimized out>) at sv.c​:7061
#6 0x00007f96b037144d in S_SvREFCNT_dec_NN (sv=<optimized out>) at inline.h​:200
#7 Perl_free_tmps () at scope.c​:207
#8 0x00007f96afd66dc5 in perl_run (my_perl=<optimized out>) at perl.c​:2456
#9 0x00007f96afc52814 in main (argc=<optimized out>, argv=<optimized
out>, env=<optimized out>) at perlmain.c​:123

Perl Info

Flags:
    category=core
    severity=medium

Site configuration information for perl 5.25.9:

Configured by root at Sat Jan 14 02:25:05 MSK 2017.

Summary of my perl5 (revision 5 version 25 subversion 9) configuration:
  Commit id: cbe2fc5001aa59cdc73e04cc35e097a2ecfbeec0
  Platform:
    osname=linux
    osvers=3.16.0-4-amd64
    archname=x86_64-linux
    uname='linux dorothy 3.16.0-4-amd64 #1 smp debian 3.16.36-1+deb8u2
(2016-10-19) x86_64 gnulinux '
    config_args='-des -Dusedevel -DDEBUGGING -Dcc=afl-clang-fast
-Doptimize=-O0 -g -ggdb3'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=undef
    usemultiplicity=undef
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    bincompat5005=undef
  Compiler:
    cc='afl-clang-fast'
    ccflags ='-DDEBUGGING -fno-strict-aliasing -pipe
-fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE
-D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2'
    optimize='-O0 -g -ggdb3'
    cppflags='-DDEBUGGING -fno-strict-aliasing -pipe
-fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='4.2.1 Compatible Clang 3.9.1 (tags/RELEASE_391/rc2)'
    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='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='afl-clang-fast'
    ldflags =' -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/llvm-3.9/bin/../lib/clang/3.9.1/lib
/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-2.24.so
    so=so
    useshrplib=false
    libperl=libperl.a
    gnulibc_version='2.24'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E'
    cccdlflags='-fPIC'
    lddlflags='-shared -O0 -g -ggdb3 -L/usr/local/lib -fstack-protector-strong'



@INC for perl 5.25.9:
    lib
    /usr/local/lib/perl5/site_perl/5.25.9/x86_64-linux
    /usr/local/lib/perl5/site_perl/5.25.9
    /usr/local/lib/perl5/5.25.9/x86_64-linux
    /usr/local/lib/perl5/5.25.9


Environment for perl 5.25.9:
    HOME=/home/afl
    LANG=en_US.UTF-8
    LANGUAGE=en_US:en
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/afl/perlbrew/bin:/home/afl/perlbrew/perls/perl-5.22.1/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
    PERLBREW_BASHRC_VERSION=0.78
    PERLBREW_HOME=/home/afl/.perlbrew
    PERLBREW_MANPATH=/home/afl/perlbrew/perls/perl-5.22.1/man
    PERLBREW_PATH=/home/afl/perlbrew/bin:/home/afl/perlbrew/perls/perl-5.22.1/bin
    PERLBREW_PERL=perl-5.22.1
    PERLBREW_ROOT=/home/afl/perlbrew
    PERLBREW_VERSION=0.78
    PERL_BADLANG (unset)
    SHELL=/usr/bin/zsh

[p5pRT]

From @iabyn

On Sun, Jan 29, 2017 at 03​:16​:24AM -0800, Sergey Aleynikov wrote​:

While fuzzing perl v5.25.9-35-g32207c637b built with afl and run
under libdislocator, I found the following program

a{%0=local$0,%0=0}

to cause an assertion failure on debugging builds and crash on regular builds.
This is a regression in blead, bisect points to

8b0c337 is the first bad commit
commit 8b0c337
Author​: David Mitchell <davem@​iabyn.com>
Date​: Wed Oct 5 10​:10​:56 2016 +0100

Better optimise array and hash assignment

\[perl \#127999\] Slowdown in split \+ list assign

Its a stack-not-refcounted issue.

The code can be simplified to

  @​a = (((%h) = ("k",1)), %h = ("k",2));

at the start of the second assignment to %h, %h is cleared, leaving the
'1' SV on the stack as a freed value. Whether perl assert fails or not
just depends on whether that freed SV happens to get reallocated before it
gets accessed as a stack value in a place that checks it for being a valid
SV. Before that commit, printing "[@​a]\n" gives​:

  [k 2 k 2]

which shows that the SV gets reallocated and has '2' assigned to it; on
blead, you get

  [k k 2]

meaning it hasn't been reallocated because the newer pp_assign() code
is better at skipping unnecessary copying.

--
The crew of the Enterprise encounter an alien life form which is
surprisingly neither humanoid nor made from pure energy.
  -- Things That Never Happen in "Star Trek" #22

[p5pRT]

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