[Bug malloc/17344] New: Enhance glibc metadata hardening with the attached patch

["scarybeasts at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=17344

            Bug ID: 17344
           Summary: Enhance glibc metadata hardening with the attached
                    patch
           Product: glibc
           Version: 2.21
            Status: NEW
          Severity: normal
          Priority: P2
         Component: malloc
          Assignee: unassigned at sourceware dot org
          Reporter: scarybeasts at gmail dot com

Created attachment 7769
  --> https://sourceware.org/bugzilla/attachment.cgi?id=7769&action=edit
Check linked list integrity for the large sized chunk list too.

As a follow-on from my recent glibc exploit:

http://googleprojectzero.blogspot.com/2014/08/the-poisoned-nul-byte-2014-edition.html

I'd have really been slowed down, perhaps even stopped, if the the existing
metadata hardening tricks were extended to one more place. I've attached a
patch. It checks doubly-linked list integrity on unlink in one more place: the
linked list for larger-sized chunks.

Please consider applying it. There was already an assert() for this check, this
patch simply elevates this from an assert() to a runtime check.

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