One of usual fuzzer fake CVEs.

This is basically a similar "problem" like initially reported in
  https://sourceware.org/bugzilla/show_bug.cgi?id=23008
where I actually analyzed it.  The problem is that C++ mangled names
have a recursive structure.  For demonstration purposes let's assume that the
character 'F' in a mangled name means "here come nested template arguments,
described next", then you need to recurse down to decode those nested args,
and if the next character is 'F' as well, you just recurse down again.  So
a mangled "name" with a million 'F' characters in succession will need
a recursion depth of a million.

So, when you feed the demangler such a name a stack overflow is expected.
Exactly when the overflow occurs depends on how the demangler is compiled,
i.e. how much stack space is needed from one to the next recursion level
(sometimes the recursion is tail recursion, so in some compilation modes
can even be elided and so lead to non-exhaustion).

Many characters of the mangled names have this property, so there are multiple
variants of names that all lead to stack exhaustion, so the fuzzers were able
to create many different testcases:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85122 (aka bugzilla PR23008)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85452
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87335
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87636
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87675
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87681

Unfortunately they now also started to submit fake CVEs for these, like this
one (CVE-2018-18701) or CVE-2018-18700 (aka bug 87681).

If libiberty ever implements a check for this (which essentially can only be an
arbitrary limit, which is frowned upon, especially as it must be very small, as
people might have their stack limit set very low) fine, if not, also fine.
Until then feeding such names to any demangling tool leads to stack exhaustion
and hence segfault.  Like any other memory exhaustion not a security bug.

As Michael said, this seems to be one of a large number of duplicates.

At least CVE-2018-18484, CVE-2018-18701, and CVE-2018-18700 seems to be a duplicates. I can only reproduce one of them via setting a lower ulimit -s, and the crashes all appear to be in cp-demangle.c. The call flows are similar yet slightly different. My guess is that a recursion limit would fix all of these hence they are the same root issue.

If upstream agrees, the duplicate CVE assignments can potentially be rejected. Let me know if anyone else has any evidence or arguments that these are different -- it is possible I made a mistake in the analysis.

My last comment was a bit confusing. I can reproduce 2/3 on a standard system, and the other 1/3 requires dropping ulimit -s down a bit. (to 4096).

(In reply to Scott Gayou from comment #3)
> My last comment was a bit confusing. I can reproduce 2/3 on a standard
> system, and the other 1/3 requires dropping ulimit -s down a bit. (to 4096).

Hi，

I don't think you've made a clear analysis of the problem. This has nothing to do with how much stack memory you set up. No matter how big your stack memory is, it can still run out. The test case only give a small number of characters. As you can imagine, you can still run out of memory by giving a lot of characters.

In detail, the program requires the amount of resource such as time, memory, power, etc. Memory exhaustion problems in the server can occur circumstantially when programs are provided with inputs that exhibit worst-case behavior. However, the high space complexity of the algorithm or poorly-designed programs consume much more memory than necessary under well-conceived inputs. In particular, stack memory is very limited. An attacker may use own function call or multiple functions to call each other, exhausting stack memory. In other words, no matter how large your stack memory is, it will always run out(by given more "Z" or "U"). No matter how big you set it up, it's ultimately limited. 

The problem itself is very difficult to fix. The problem is that C++ mangled names have a recursive structure. Simple restriction cycles are not necessarily good. Moreover, these examples give different stack frames. This is cause by giving different string input. Some are call itself. Some are call different function. In fact, it's hard to set recursive limits on every function. Recursion limit would not fix all of these hence they are different root cause(Loop calls involving six functions in a finite function stack frame).

Author: nickc
Date: Fri Dec  7 10:33:30 2018
New Revision: 266886

URL: https://gcc.gnu.org/viewcvs?rev=266886&root=gcc&view=rev
Log:
Add a recursion limit to libiberty's demangling code.  The limit is enabled by default, but can be disabled via a new demangling option.

include	* demangle.h (DMGL_NO_RECURSE_LIMIT): Define.
        (DEMANGLE_RECURSION_LIMIT): Define

	PR 87681
	PR 87675
	PR 87636
	PR 87350
	PR 87335
libiberty * cp-demangle.h (struct d_info): Add recursion_level field.
	* cp-demangle.c (d_function_type): Add recursion counter.
	If the recursion limit is reached and the check is not disabled,
	then return with a failure result.
	(cplus_demangle_init_info): Initialise the recursion_level field.
        (d_demangle_callback): If the recursion limit is enabled, check
	for a mangled string that is so long that there is not enough
	stack space for the local arrays.
        * cplus-dem.c (struct work): Add recursion_level field.
	(squangle_mop_up): Set the numb and numk fields to zero.
	(work_stuff_copy_to_from): Handle the case where a btypevec or 
	ktypevec field is NULL.
	(demangle_nested_args): Add recursion counter.  If
	the recursion limit is not disabled and reached, return with a
	failure result.

Modified:
    trunk/include/ChangeLog
    trunk/include/demangle.h
    trunk/libiberty/ChangeLog
    trunk/libiberty/cp-demangle.c
    trunk/libiberty/cp-demangle.h
    trunk/libiberty/cplus-dem.c

Fixed by commit 266886.

Should we expect this fix to be in Binutil 2.32?

(In reply to Tanaya Patil from comment #7)
> Should we expect this fix to be in Binutil 2.32?

Yes. :-)