Bug 71696 - Libiberty Demangler segfaults (6)
Summary: Libiberty Demangler segfaults (6)
Alias: None
Product: gcc
Classification: Unclassified
Component: c++ (show other bugs)
Version: unknown
: P3 normal
Target Milestone: ---
Assignee: Not yet assigned to anyone
Depends on:
Reported: 2016-06-29 13:42 UTC by Marcel Böhme
Modified: 2016-08-04 16:54 UTC (History)
2 users (show)

See Also:
Known to work:
Known to fail:
Last reconfirmed: 2016-06-30 00:00:00


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Description Marcel Böhme 2016-06-29 13:42:52 UTC
A stackoverflow in the libiberty demangler causes its host application to crash on a tainted branch instruction. The problem is caused by a self-reference in a mangled type string that is "remembered" for later reference. This leads to an infinite recursion during the demangling.

How to reproduce:
$ valgrind cxxfilt __33%00000000000000000000__S8_00T0000T0
==30184== Memcheck, a memory error detector
==30184== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==30184== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==30184== Command: ../../binutils_git5/libiberty/testsuite/test-demangle
==30184== Stack overflow in thread 1: can't grow stack to 0xffe801ff8

$ valgrind cxxfilt __10%0__S4_0T0T0

Analysis: The demangler "remembers" mangled types that can later be referenced in the mangled string. In this case the complete string is remembered in work->typevec[0] before it is demangled in cplus-dem.c:4534. Now, a part of the mangled string ("T0000") references the remembered type stored at work->typevec[0] which is supposed to be demangled as well (cplus-dem.c:3632).

The tool was found with a more efficient version of AFL, called AFL-Fast.
I am preparing a patch.
Comment 1 Martin Liška 2016-06-30 08:10:35 UTC
Comment 2 Jeffrey A. Law 2016-08-04 16:53:50 UTC
Author: law
Date: Thu Aug  4 16:53:18 2016
New Revision: 239143

URL: https://gcc.gnu.org/viewcvs?rev=239143&root=gcc&view=rev
2016-08-04  Marcel Böhme  <boehme.marcel@gmail.com>

	PR c++/71696
	* cplus-dem.c: Prevent infinite recursion when there is a cycle
	in the referencing of remembered mangled types.
	(work_stuff): New stack to keep track of the remembered mangled
	types that are currently being processed.
	(push_processed_type): New method to push currently processed
	remembered type onto the stack.
	(pop_processed_type): New method to pop currently processed
	remembered type from the stack.
	(work_stuff_copy_to_from): Copy values of new variables.
	(delete_non_B_K_work_stuff): Free stack memory.
	(demangle_args): Push/Pop currently processed remembered type.
	(do_type): Do not demangle a cyclic reference and push/pop
	referenced remembered type.

Comment 3 Jeffrey A. Law 2016-08-04 16:54:04 UTC
Should be fixed on trunk now.