[Bug libc/14277] Pointer used after free'd

["law at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14277

--- Comment #2 from law at redhat dot com 2012-06-21 18:00:06 UTC ---
M_PERTURB does work for realloc (which just calls free internally).  I can even
verify that it puts my perturb bytes into the free'd memory.  All fine and
good.

Unfortunately after installing my perturb byte, something else inside malloc
decides to put the value 0 into the first 4 bytes of the free'd memory,
overwriting my nice invalid pointer perturb byte ;(

That happens to correspond to transmem_list->next.  When we then try to use the
value, it just looks like a null pointer, which the code assumes is the end of
the list.  So M_PERTURB isn't particularly helpful in generating a testcase for
this bug.

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