Bug 22026 - iconv_open: heap overflow on gconv_init failure
Summary: iconv_open: heap overflow on gconv_init failure
Alias: None
Product: glibc
Classification: Unclassified
Component: locale (show other bugs)
Version: 2.26
: P2 normal
Target Milestone: 2.27
Assignee: Florian Weimer
Depends on:
Reported: 2017-08-29 13:03 UTC by Florian Weimer
Modified: 2017-08-29 15:36 UTC (History)
0 users

See Also:
Last reconfirmed:
fweimer: security-


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Description Florian Weimer 2017-08-29 13:03:27 UTC
gen_steps decrements step_cnt twice on an error path.

                  if (__builtin_expect (status, __GCONV_OK) != __GCONV_OK)
                      failed = 1;
                      /* Make sure we unload this modules.  */
                      result[step_cnt].__end_fct = NULL;

As a result, the update of __end_fct is out of bounds:

==10047== Invalid write of size 8
==10047==    at 0x4C36B91: gen_steps (gconv_db.c:333)
==10047==    by 0x4C36B91: find_derivation (gconv_db.c:691)
==10047==    by 0x4C36F5D: __gconv_find_transform (gconv_db.c:792)
==10047==    by 0x4C359D6: __gconv_open (gconv_open.c:110)
==10047==    by 0x4C35568: iconv_open (iconv_open.c:71)
==10047==    by 0x401413: do_test (tst-gconv-init-failure.c:50)
==10047==    by 0x401B32: support_test_main (support_test_main.c:321)
==10047==    by 0x401264: main (test-driver.c:164)
==10047==  Address 0x5013288 is 24 bytes after a block of size 32 in arena "client"

I don't we ship any gconv modules where gconv_init can actually fail (on a correctly configured system), so I'm flagging this as security-.
Comment 1 Florian Weimer 2017-08-29 13:13:01 UTC
__end_fct must also be properly mangled on the error handling path.
Comment 2 cvs-commit@gcc.gnu.org 2017-08-29 15:36:02 UTC
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- Log -----------------------------------------------------------------

commit 251bccfa1fcb3568e43546b0df33e052889406c1
Author: Florian Weimer <fweimer@redhat.com>
Date:   Tue Aug 29 17:33:58 2017 +0200

    iconv_open: Fix heap corruption on gconv_init failure [BZ #22026]
    Also mangle the __end_fct function pointer on the error handling


Summary of changes:
 ChangeLog                          |   16 ++++++++++
 iconv/Makefile                     |   14 ++++++++
 iconv/gconv_db.c                   |    9 ++++-
 iconv/test-gconv-modules           |   23 ++++++++++++++
 iconv/tst-gconv-init-failure-mod.c |   49 ++++++++++++++++++++++++++++++
 iconv/tst-gconv-init-failure.c     |   58 ++++++++++++++++++++++++++++++++++++
 6 files changed, 167 insertions(+), 2 deletions(-)
 create mode 100644 iconv/test-gconv-modules
 create mode 100644 iconv/tst-gconv-init-failure-mod.c
 create mode 100644 iconv/tst-gconv-init-failure.c
Comment 3 Florian Weimer 2017-08-29 15:36:26 UTC
Fixed in 2.27.