[Bug network/18665] In send_dg, the recvfrom function is NOT always using the buffer size of a newly created buffer (CVE-2015-7547)

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https://sourceware.org/bugzilla/show_bug.cgi?id=18665

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=33f372c7df351d49db04aab021931f32ef2ef612

commit 33f372c7df351d49db04aab021931f32ef2ef612
Author: Carlos O'Donell <carlos@systemhalted.org>
Date:   Tue Feb 16 21:26:37 2016 -0500

    CVE-2015-7547: getaddrinfo() stack-based buffer overflow (Bug 18665).

    * A stack-based buffer overflow was found in libresolv when invoked from
      libnss_dns, allowing specially crafted DNS responses to seize control
      of execution flow in the DNS client.  The buffer overflow occurs in
      the functions send_dg (send datagram) and send_vc (send TCP) for the
      NSS module libnss_dns.so.2 when calling getaddrinfo with AF_UNSPEC
      family.  The use of AF_UNSPEC triggers the low-level resolver code to
      send out two parallel queries for A and AAAA.  A mismanagement of the
      buffers used for those queries could result in the response of a query
      writing beyond the alloca allocated buffer created by
      _nss_dns_gethostbyname4_r.  Buffer management is simplified to remove
      the overflow.  Thanks to the Google Security Team and Red Hat for
      reporting the security impact of this issue, and Robert Holiday of
      Ciena for reporting the related bug 18665. (CVE-2015-7547)

    See also:
    https://sourceware.org/ml/libc-alpha/2016-02/msg00416.html
    https://sourceware.org/ml/libc-alpha/2016-02/msg00418.html

    (cherry picked from commit e9db92d3acfe1822d56d11abcea5bfc4c41cf6ca)
    (cherry picked from commit 16d0a0ce7613552301786bf05d7eba8784b5732c)

-----------------------------------------------------------------------

Summary of changes:
 resolv/nss_dns/dns-host.c |  111 +++++++++++++++++++-
 resolv/res_query.c        |    3 +
 resolv/res_send.c         |  264 +++++++++++++++++++++++++++++++++------------
 3 files changed, 309 insertions(+), 69 deletions(-)

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