[ECOS] DNS race condition and patch

[Will Lentz]

Hi,

There's a race condition in
packages/net/ns/dns/current/include/dns_impl.inl and dns.c.

Here's a quick example of how the current code may cause a problem:
 1) Call cyg_dns_res_start() in thread #1.
    Assume the connect() call blocks for a few seconds.
    Note that at this point 's' is valid, but 'ptdindex' in
uninitialized or invalid.
 2) While thread #1 is blocked, call gethostbyname() (or
gethostbyaddr()) in thread #2.
    The call to free_stored_hent() assumes 'ptdindex' is valid, but it
is not.
    If you have asserts on, cyg_thread_get_data(ptdindex) will hit an
assert or return
    a bogus pointer value that may get passed to free().

The attached fix:
 - puts 's' and free_stored_hent()/ptdindex inside the mutex lock so
they are
   always consistent with each other.
 - makes 'init' file-visible so it can protect against accessing an
uninitialized mutex.

Thanks,
Will
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