CVE-2012-3509: objalloc_alloc integer overflows in libiberty

[Florian Weimer <fw () deneb enyo de>]

Sang Kil Cha discovered that _objalloc_alloc does not guard the
addition of CHUNK_HEADER_SIZE to the length against overflow.  This
can cause _objalloc_alloc to return a pointer to a memory region which
is smaller than expected.

The pointer alignment arithmetic in the objalloc_alloc macro misses an
overflow check as well, with similar consequences.

GCC bug:

http://gcc.gnu.org/bugzilla/show_activity.cgi?id=54411

Patch under review:

http://gcc.gnu.org/ml/gcc-patches/2012-08/msg01986.html

(I believe GCC has the master copy of this file, but does not use it
itself.  libiberty is part of binutils and GDB, too.)