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SEGV reading through null HEK* in hv_ename_add #14512

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p5pRT opened this issue Feb 16, 2015 · 8 comments
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@p5pRT p5pRT commented Feb 16, 2015

Migrated from rt.perl.org#123847 (status was 'resolved')

Searchable as RT123847$

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@p5pRT p5pRT commented Feb 16, 2015

From @hvds

AFL (<http​://lcamtuf.coredump.cx/afl/>) finds this​:

% ./miniperl -e '%0=*​:=*​::​::=0'
Segmentation fault (core dumped)
%

The code looks similar to the glob overwriting cases in [perl #123710], but the failure mode is quite different​:

Program received signal SIGSEGV, Segmentation fault.
0x000000000056afbc in Perl_hv_ename_add (hv=0xa56108, name=0xa62460 "​:",
  len=1, flags=0) at hv.c​:2342
2342 (HEK_UTF8(*hekp) || (flags & SVf_UTF8))
(gdb) where
#0 0x000000000056afbc in Perl_hv_ename_add (hv=0xa56108, name=0xa62460 "​:",
  len=1, flags=0) at hv.c​:2342
#1 0x000000000055a651 in S_mro_gather_and_rename (stashes=0xa557c0,
  seen_stashes=0xa55790, stash=0xa56108, oldstash=0x0, namesv=0xa61400)
  at mro.c​:992
#2 0x000000000055953b in Perl_mro_package_moved (stash=0xa56108,
  oldstash=0x0, gv=0xa613e8, flags=0) at mro.c​:844
#3 0x00000000005a9e33 in S_glob_assign_glob (dstr=0xa613e8, sstr=0xa61418,
  dtype=9) at sv.c​:4005
#4 0x00000000005afa88 in Perl_sv_setsv_flags (dstr=0xa613e8, sstr=0xa61418,
  flags=1538) at sv.c​:4426
#5 0x0000000000574add in Perl_pp_sassign () at pp_hot.c​:231
#6 0x000000000052a13d in Perl_runops_debug () at dump.c​:2231
#7 0x00000000004098c7 in S_run_body (oldscope=1) at perl.c​:2423
#8 0x0000000000408f0b in perl_run (my_perl=0xa40010) at perl.c​:2346
#9 0x00000000004508d1 in main (argc=3, argv=0x7fffffffe638,
  env=0x7fffffffe658) at miniperlmain.c​:122
(gdb) p hekp
$1 = (HEK **) 0xa5f820
(gdb) p *hekp
$2 = (HEK *) 0x0
(gdb) p /x *hv
$3 = {sv_any = 0xa47ec0, sv_refcnt = 0x1, sv_flags = 0x3200000c, sv_u = {
  svu_pv = 0xa59150, svu_iv = 0xa59150, svu_uv = 0xa59150, svu_nv = 0x0,
  svu_rv = 0xa59150, svu_rx = 0xa59150, svu_array = 0xa59150,
  svu_hash = 0xa59150, svu_gp = 0xa59150, svu_fp = 0xa59150}}
(gdb) p *aux
$4 = {xhv_name_u = {xhvnameu_name = 0xa5f820, xhvnameu_names = 0xa5f820},
  xhv_backreferences = 0x0, xhv_eiter = 0x0, xhv_riter = -1,
  xhv_name_count = -2, xhv_mro_meta = 0xa5f4e0, xhv_rand = 1738015991,
  xhv_last_rand = 1738015991, xhv_fill_lazy = 0, xhv_aux_flags = 0}
(gdb) p aux->xhv_name_u.xhvnameu_names[0]@​2
$5 = {0x0, 0xa4d368}

Not sure what's supposed to be happening here - the else branch (when not aux->xhv_name_count) clearly knows when it stores existing_name to xhvnameu_names[0] that it might be NULL, that's why our name_count is -2, so how can it be right to loop as far as xhvnameu_names[0] in the if branch?

Hugo

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@p5pRT p5pRT commented Mar 3, 2015

From @cpansprout

On Mon Feb 16 04​:37​:51 2015, hv wrote​:

AFL (<http​://lcamtuf.coredump.cx/afl/>) finds this​:

% ./miniperl -e '%0=*​:=*​::​::=0'
Segmentation fault (core dumped)
%

The code looks similar to the glob overwriting cases in [perl
#123710], but the failure mode is quite different​:

Program received signal SIGSEGV, Segmentation fault.
0x000000000056afbc in Perl_hv_ename_add (hv=0xa56108, name=0xa62460
"​:",
len=1, flags=0) at hv.c​:2342
2342 (HEK_UTF8(*hekp) || (flags & SVf_UTF8))
(gdb) where
#0 0x000000000056afbc in Perl_hv_ename_add (hv=0xa56108,
name=0xa62460 "​:",
len=1, flags=0) at hv.c​:2342
#1 0x000000000055a651 in S_mro_gather_and_rename (stashes=0xa557c0,
seen_stashes=0xa55790, stash=0xa56108, oldstash=0x0,
namesv=0xa61400)
at mro.c​:992
#2 0x000000000055953b in Perl_mro_package_moved (stash=0xa56108,
oldstash=0x0, gv=0xa613e8, flags=0) at mro.c​:844
#3 0x00000000005a9e33 in S_glob_assign_glob (dstr=0xa613e8,
sstr=0xa61418,
dtype=9) at sv.c​:4005
#4 0x00000000005afa88 in Perl_sv_setsv_flags (dstr=0xa613e8,
sstr=0xa61418,
flags=1538) at sv.c​:4426
#5 0x0000000000574add in Perl_pp_sassign () at pp_hot.c​:231
#6 0x000000000052a13d in Perl_runops_debug () at dump.c​:2231
#7 0x00000000004098c7 in S_run_body (oldscope=1) at perl.c​:2423
#8 0x0000000000408f0b in perl_run (my_perl=0xa40010) at perl.c​:2346
#9 0x00000000004508d1 in main (argc=3, argv=0x7fffffffe638,
env=0x7fffffffe658) at miniperlmain.c​:122
(gdb) p hekp
$1 = (HEK **) 0xa5f820
(gdb) p *hekp
$2 = (HEK *) 0x0
(gdb) p /x *hv
$3 = {sv_any = 0xa47ec0, sv_refcnt = 0x1, sv_flags = 0x3200000c, sv_u
= {
svu_pv = 0xa59150, svu_iv = 0xa59150, svu_uv = 0xa59150, svu_nv =
0x0,
svu_rv = 0xa59150, svu_rx = 0xa59150, svu_array = 0xa59150,
svu_hash = 0xa59150, svu_gp = 0xa59150, svu_fp = 0xa59150}}
(gdb) p *aux
$4 = {xhv_name_u = {xhvnameu_name = 0xa5f820, xhvnameu_names =
0xa5f820},
xhv_backreferences = 0x0, xhv_eiter = 0x0, xhv_riter = -1,
xhv_name_count = -2, xhv_mro_meta = 0xa5f4e0, xhv_rand =
1738015991,
xhv_last_rand = 1738015991, xhv_fill_lazy = 0, xhv_aux_flags = 0}
(gdb) p aux->xhv_name_u.xhvnameu_names[0]@​2
$5 = {0x0, 0xa4d368}

Not sure what's supposed to be happening here - the else branch (when
not aux->xhv_name_count) clearly knows when it stores existing_name to
xhvnameu_names[0] that it might be NULL, that's why our name_count is
-2, so how can it be right to loop as far as xhvnameu_names[0] in the
if branch?

Bisect​:

1f656fc is the first bad commit
commit 1f656fc
Author​: Father Chrysostomos <sprout@​cpan.org>
Date​: Fri Apr 15 22​:33​:31 2011 -0700

  Followup to 088225f/[perl #88132]​: packages ending with :

--

Father Chrysostomos

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@p5pRT p5pRT commented Mar 3, 2015

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

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@p5pRT p5pRT commented Mar 12, 2015

From @cpansprout

On Mon Mar 02 22​:09​:39 2015, sprout wrote​:

On Mon Feb 16 04​:37​:51 2015, hv wrote​:

AFL (<http​://lcamtuf.coredump.cx/afl/>) finds this​:

% ./miniperl -e '%0=*​:=*​::​::=0'
Segmentation fault (core dumped)
%

The code looks similar to the glob overwriting cases in [perl
#123710], but the failure mode is quite different​:

Program received signal SIGSEGV, Segmentation fault.
0x000000000056afbc in Perl_hv_ename_add (hv=0xa56108, name=0xa62460
"​:",
len=1, flags=0) at hv.c​:2342
2342 (HEK_UTF8(*hekp) || (flags & SVf_UTF8))
(gdb) where
#0 0x000000000056afbc in Perl_hv_ename_add (hv=0xa56108,
name=0xa62460 "​:",
len=1, flags=0) at hv.c​:2342
#1 0x000000000055a651 in S_mro_gather_and_rename (stashes=0xa557c0,
seen_stashes=0xa55790, stash=0xa56108, oldstash=0x0,
namesv=0xa61400)
at mro.c​:992
#2 0x000000000055953b in Perl_mro_package_moved (stash=0xa56108,
oldstash=0x0, gv=0xa613e8, flags=0) at mro.c​:844
#3 0x00000000005a9e33 in S_glob_assign_glob (dstr=0xa613e8,
sstr=0xa61418,
dtype=9) at sv.c​:4005
#4 0x00000000005afa88 in Perl_sv_setsv_flags (dstr=0xa613e8,
sstr=0xa61418,
flags=1538) at sv.c​:4426
#5 0x0000000000574add in Perl_pp_sassign () at pp_hot.c​:231
#6 0x000000000052a13d in Perl_runops_debug () at dump.c​:2231
#7 0x00000000004098c7 in S_run_body (oldscope=1) at perl.c​:2423
#8 0x0000000000408f0b in perl_run (my_perl=0xa40010) at perl.c​:2346
#9 0x00000000004508d1 in main (argc=3, argv=0x7fffffffe638,
env=0x7fffffffe658) at miniperlmain.c​:122
(gdb) p hekp
$1 = (HEK **) 0xa5f820
(gdb) p *hekp
$2 = (HEK *) 0x0
(gdb) p /x *hv
$3 = {sv_any = 0xa47ec0, sv_refcnt = 0x1, sv_flags = 0x3200000c, sv_u
= {
svu_pv = 0xa59150, svu_iv = 0xa59150, svu_uv = 0xa59150, svu_nv =
0x0,
svu_rv = 0xa59150, svu_rx = 0xa59150, svu_array = 0xa59150,
svu_hash = 0xa59150, svu_gp = 0xa59150, svu_fp = 0xa59150}}
(gdb) p *aux
$4 = {xhv_name_u = {xhvnameu_name = 0xa5f820, xhvnameu_names =
0xa5f820},
xhv_backreferences = 0x0, xhv_eiter = 0x0, xhv_riter = -1,
xhv_name_count = -2, xhv_mro_meta = 0xa5f4e0, xhv_rand =
1738015991,
xhv_last_rand = 1738015991, xhv_fill_lazy = 0, xhv_aux_flags = 0}
(gdb) p aux->xhv_name_u.xhvnameu_names[0]@​2
$5 = {0x0, 0xa4d368}

Not sure what's supposed to be happening here - the else branch (when
not aux->xhv_name_count) clearly knows when it stores existing_name to
xhvnameu_names[0] that it might be NULL, that's why our name_count is
-2, so how can it be right to loop as far as xhvnameu_names[0] in the
if branch?

Bisect​:

1f656fc is the first bad commit
commit 1f656fc
Author​: Father Chrysostomos <sprout@​cpan.org>
Date​: Fri Apr 15 22​:33​:31 2011 -0700

Followup to 088225f/\[perl \#88132\]&#8203;: packages ending with :

Here is a clearer example, which goes back to 5.14​:

$ ./miniperl -e '%0; *bar​::=*foo​::=0'

The %0 hash needs to be vivified beforehand, and the two globs assigned to need to be stash globs (fq names ending in :​:).

The logic in hv_ename_add is wrong, and probably has been so since I wrote it.

--

Father Chrysostomos

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@p5pRT p5pRT commented Mar 12, 2015

From @cpansprout

Fixed in 3d50185.

--

Father Chrysostomos

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@p5pRT p5pRT commented Mar 12, 2015

@cpansprout - Status changed from 'open' to 'pending release'

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@p5pRT p5pRT commented Jun 2, 2015

From @khwilliamson

Thank you for submitting this ticket.

The issue should now be resolved with the release today of Perl v5.22, which is available at http​://www.perl.org/get.html
--
Karl Williamson for the Perl 5 team

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@p5pRT p5pRT commented Jun 2, 2015

@khwilliamson - Status changed from 'pending release' to 'resolved'

@p5pRT p5pRT closed this Jun 2, 2015
@p5pRT p5pRT added the Severity Low label Oct 19, 2019
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