glibc: Security fix CVE-2015-7547

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

(From OE-Core rev: 3f454361fc323119c2850aeb239171e40d085161)

Signed-off-by: Armin Kuster <akuster@mvista.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 642 insertions, 0 deletions

diff --git a/meta/recipes-core/glibc/glibc/CVE-2015-7547.patch b/meta/recipes-core/glibc/glibc/CVE-2015-7547.patch
new file mode 100644
index 0000000000..4e539f8497
--- /dev/null
+++ b/meta/recipes-core/glibc/glibc/CVE-2015-7547.patch
@@ -0,0 +1,642 @@
+From e9db92d3acfe1822d56d11abcea5bfc4c41cf6ca Mon Sep 17 00:00:00 2001
+From: Carlos O'Donell <carlos@systemhalted.org>
+Date: Tue, 16 Feb 2016 21:26:37 -0500
+Subject: [PATCH] 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
+
+Upstream-Status: Backport
+CVE: CVE-2015-7547
+
+https://sourceware.org/git/?p=glibc.git;a=commit;h=e9db92d3acfe1822d56d11abcea5bfc4c41cf6ca
+minor tweeking to apply to Changelog and res_send.c
+
+Signed-off-by: Armin Kuster <akuster@mvista.com>
+
+---
+ ChangeLog                 |  17 ++-
+ NEWS                      |  14 +++
+ resolv/nss_dns/dns-host.c | 111 +++++++++++++++++++-
+ resolv/res_query.c        |   3 +
+ resolv/res_send.c         | 260 +++++++++++++++++++++++++++++++++++-----------
+ 5 files changed, 339 insertions(+), 66 deletions(-)
+
+Index: git/NEWS
+===================================================================
+--- git.orig/NEWS
++++ git/NEWS
+@@ -105,6 +105,20 @@ Security related changes:
+   depending on the length of the string passed as an argument to the
+   functions.  Reported by Joseph Myers.
+ 
++* 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)
++
+ * The following bugs are resolved with this release:
+ 
+   6652, 10672, 12674, 12847, 12926, 13862, 14132, 14138, 14171, 14498,
+Index: git/resolv/nss_dns/dns-host.c
+===================================================================
+--- git.orig/resolv/nss_dns/dns-host.c
++++ git/resolv/nss_dns/dns-host.c
+@@ -1031,7 +1031,10 @@ gaih_getanswer_slice (const querybuf *an
+   int h_namelen = 0;
+ 
+   if (ancount == 0)
+-    return NSS_STATUS_NOTFOUND;
++    {
++      *h_errnop = HOST_NOT_FOUND;
++      return NSS_STATUS_NOTFOUND;
++    }
+ 
+   while (ancount-- > 0 && cp < end_of_message && had_error == 0)
+     {
+@@ -1208,7 +1211,14 @@ gaih_getanswer_slice (const querybuf *an
+   /* Special case here: if the resolver sent a result but it only
+      contains a CNAME while we are looking for a T_A or T_AAAA record,
+      we fail with NOTFOUND instead of TRYAGAIN.  */
+-  return canon == NULL ? NSS_STATUS_TRYAGAIN : NSS_STATUS_NOTFOUND;
++  if (canon != NULL)
++    {
++      *h_errnop = HOST_NOT_FOUND;
++      return NSS_STATUS_NOTFOUND;
++    }
++
++  *h_errnop = NETDB_INTERNAL;
++  return NSS_STATUS_TRYAGAIN;
+ }
+ 
+ 
+@@ -1222,11 +1232,101 @@ gaih_getanswer (const querybuf *answer1,
+ 
+   enum nss_status status = NSS_STATUS_NOTFOUND;
+ 
++  /* Combining the NSS status of two distinct queries requires some
++     compromise and attention to symmetry (A or AAAA queries can be
++     returned in any order).  What follows is a breakdown of how this
++     code is expected to work and why. We discuss only SUCCESS,
++     TRYAGAIN, NOTFOUND and UNAVAIL, since they are the only returns
++     that apply (though RETURN and MERGE exist).  We make a distinction
++     between TRYAGAIN (recoverable) and TRYAGAIN' (not-recoverable).
++     A recoverable TRYAGAIN is almost always due to buffer size issues
++     and returns ERANGE in errno and the caller is expected to retry
++     with a larger buffer.
++
++     Lastly, you may be tempted to make significant changes to the
++     conditions in this code to bring about symmetry between responses.
++     Please don't change anything without due consideration for
++     expected application behaviour.  Some of the synthesized responses
++     aren't very well thought out and sometimes appear to imply that
++     IPv4 responses are always answer 1, and IPv6 responses are always
++     answer 2, but that's not true (see the implementation of send_dg
++     and send_vc to see response can arrive in any order, particularly
++     for UDP). However, we expect it holds roughly enough of the time
++     that this code works, but certainly needs to be fixed to make this
++     a more robust implementation.
++
++     ----------------------------------------------
++     | Answer 1 Status /   | Synthesized | Reason |
++     | Answer 2 Status     | Status      |        |
++     |--------------------------------------------|
++     | SUCCESS/SUCCESS     | SUCCESS     | [1]    |
++     | SUCCESS/TRYAGAIN    | TRYAGAIN    | [5]    |
++     | SUCCESS/TRYAGAIN'   | SUCCESS     | [1]    |
++     | SUCCESS/NOTFOUND    | SUCCESS     | [1]    |
++     | SUCCESS/UNAVAIL     | SUCCESS     | [1]    |
++     | TRYAGAIN/SUCCESS    | TRYAGAIN    | [2]    |
++     | TRYAGAIN/TRYAGAIN   | TRYAGAIN    | [2]    |
++     | TRYAGAIN/TRYAGAIN'  | TRYAGAIN    | [2]    |
++     | TRYAGAIN/NOTFOUND   | TRYAGAIN    | [2]    |
++     | TRYAGAIN/UNAVAIL    | TRYAGAIN    | [2]    |
++     | TRYAGAIN'/SUCCESS   | SUCCESS     | [3]    |
++     | TRYAGAIN'/TRYAGAIN  | TRYAGAIN    | [3]    |
++     | TRYAGAIN'/TRYAGAIN' | TRYAGAIN'   | [3]    |
++     | TRYAGAIN'/NOTFOUND  | TRYAGAIN'   | [3]    |
++     | TRYAGAIN'/UNAVAIL   | UNAVAIL     | [3]    |
++     | NOTFOUND/SUCCESS    | SUCCESS     | [3]    |
++     | NOTFOUND/TRYAGAIN   | TRYAGAIN    | [3]    |
++     | NOTFOUND/TRYAGAIN'  | TRYAGAIN'   | [3]    |
++     | NOTFOUND/NOTFOUND   | NOTFOUND    | [3]    |
++     | NOTFOUND/UNAVAIL    | UNAVAIL     | [3]    |
++     | UNAVAIL/SUCCESS     | UNAVAIL     | [4]    |
++     | UNAVAIL/TRYAGAIN    | UNAVAIL     | [4]    |
++     | UNAVAIL/TRYAGAIN'   | UNAVAIL     | [4]    |
++     | UNAVAIL/NOTFOUND    | UNAVAIL     | [4]    |
++     | UNAVAIL/UNAVAIL     | UNAVAIL     | [4]    |
++     ----------------------------------------------
++
++     [1] If the first response is a success we return success.
++        This ignores the state of the second answer and in fact
++        incorrectly sets errno and h_errno to that of the second
++        answer.  However because the response is a success we ignore
++        *errnop and *h_errnop (though that means you touched errno on
++        success).  We are being conservative here and returning the
++        likely IPv4 response in the first answer as a success.
++
++     [2] If the first response is a recoverable TRYAGAIN we return
++        that instead of looking at the second response.  The
++        expectation here is that we have failed to get an IPv4 response
++        and should retry both queries.
++
++     [3] If the first response was not a SUCCESS and the second
++        response is not NOTFOUND (had a SUCCESS, need to TRYAGAIN,
++        or failed entirely e.g. TRYAGAIN' and UNAVAIL) then use the
++        result from the second response, otherwise the first responses
++        status is used.  Again we have some odd side-effects when the
++        second response is NOTFOUND because we overwrite *errnop and
++        *h_errnop that means that a first answer of NOTFOUND might see
++        its *errnop and *h_errnop values altered.  Whether it matters
++        in practice that a first response NOTFOUND has the wrong
++        *errnop and *h_errnop is undecided.
++
++     [4] If the first response is UNAVAIL we return that instead of
++        looking at the second response.  The expectation here is that
++        it will have failed similarly e.g. configuration failure.
++
++     [5] Testing this code is complicated by the fact that truncated
++        second response buffers might be returned as SUCCESS if the
++        first answer is a SUCCESS.  To fix this we add symmetry to
++        TRYAGAIN with the second response.  If the second response
++        is a recoverable error we now return TRYAGIN even if the first
++        response was SUCCESS.  */
++
+   if (anslen1 > 0)
+     status = gaih_getanswer_slice(answer1, anslen1, qname,
+                                  &pat, &buffer, &buflen,
+                                  errnop, h_errnop, ttlp,
+                                  &first);
++
+   if ((status == NSS_STATUS_SUCCESS || status == NSS_STATUS_NOTFOUND
+        || (status == NSS_STATUS_TRYAGAIN
+           /* We want to look at the second answer in case of an
+@@ -1242,8 +1342,15 @@ gaih_getanswer (const querybuf *answer1,
+                                                     &pat, &buffer, &buflen,
+                                                     errnop, h_errnop, ttlp,
+                                                     &first);
++      /* Use the second response status in some cases.  */
+       if (status != NSS_STATUS_SUCCESS && status2 != NSS_STATUS_NOTFOUND)
+        status = status2;
++      /* Do not return a truncated second response (unless it was
++        unavoidable e.g. unrecoverable TRYAGAIN).  */
++      if (status == NSS_STATUS_SUCCESS
++         && (status2 == NSS_STATUS_TRYAGAIN
++             && *errnop == ERANGE && *h_errnop != NO_RECOVERY))
++       status = NSS_STATUS_TRYAGAIN;
+     }
+ 
+   return status;
+Index: git/resolv/res_query.c
+===================================================================
+--- git.orig/resolv/res_query.c
++++ git/resolv/res_query.c
+@@ -396,6 +396,7 @@ __libc_res_nsearch(res_state statp,
+                  {
+                    free (*answerp2);
+                    *answerp2 = NULL;
++                   *nanswerp2 = 0;
+                    *answerp2_malloced = 0;
+                  }
+        }
+@@ -447,6 +448,7 @@ __libc_res_nsearch(res_state statp,
+                          {
+                            free (*answerp2);
+                            *answerp2 = NULL;
++                           *nanswerp2 = 0;
+                            *answerp2_malloced = 0;
+                          }
+ 
+@@ -521,6 +523,7 @@ __libc_res_nsearch(res_state statp,
+          {
+            free (*answerp2);
+            *answerp2 = NULL;
++           *nanswerp2 = 0;
+            *answerp2_malloced = 0;
+          }
+        if (saved_herrno != -1)
+Index: git/resolv/res_send.c
+===================================================================
+--- git.orig/resolv/res_send.c
++++ git/resolv/res_send.c
+@@ -1,3 +1,20 @@
++/* Copyright (C) 2016 Free Software Foundation, Inc.
++   This file is part of the GNU C Library.
++
++   The GNU C Library is free software; you can redistribute it and/or
++   modify it under the terms of the GNU Lesser General Public
++   License as published by the Free Software Foundation; either
++   version 2.1 of the License, or (at your option) any later version.
++
++   The GNU C Library is distributed in the hope that it will be useful,
++   but WITHOUT ANY WARRANTY; without even the implied warranty of
++   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
++   Lesser General Public License for more details.
++
++   You should have received a copy of the GNU Lesser General Public
++   License along with the GNU C Library; if not, see
++   <http://www.gnu.org/licenses/>.  */
++
+ /*
+  * Copyright (c) 1985, 1989, 1993
+  *    The Regents of the University of California.  All rights reserved.
+@@ -363,6 +380,8 @@ __libc_res_nsend(res_state statp, const
+ #ifdef USE_HOOKS
+        if (__glibc_unlikely (statp->qhook || statp->rhook))       {
+                if (anssiz < MAXPACKET && ansp) {
++                       /* Always allocate MAXPACKET, callers expect
++                          this specific size.  */
+                        u_char *buf = malloc (MAXPACKET);
+                        if (buf == NULL)
+                                return (-1);
+@@ -638,6 +657,77 @@ get_nsaddr (res_state statp, int n)
+     return (struct sockaddr *) (void *) &statp->nsaddr_list[n];
+ }
+ 
++/* The send_vc function is responsible for sending a DNS query over TCP
++   to the nameserver numbered NS from the res_state STATP i.e.
++   EXT(statp).nssocks[ns].  The function supports sending both IPv4 and
++   IPv6 queries at the same serially on the same socket.
++
++   Please note that for TCP there is no way to disable sending both
++   queries, unlike UDP, which honours RES_SNGLKUP and RES_SNGLKUPREOP
++   and sends the queries serially and waits for the result after each
++   sent query.  This implemetnation should be corrected to honour these
++   options.
++
++   Please also note that for TCP we send both queries over the same
++   socket one after another.  This technically violates best practice
++   since the server is allowed to read the first query, respond, and
++   then close the socket (to service another client).  If the server
++   does this, then the remaining second query in the socket data buffer
++   will cause the server to send the client an RST which will arrive
++   asynchronously and the client's OS will likely tear down the socket
++   receive buffer resulting in a potentially short read and lost
++   response data.  This will force the client to retry the query again,
++   and this process may repeat until all servers and connection resets
++   are exhausted and then the query will fail.  It's not known if this
++   happens with any frequency in real DNS server implementations.  This
++   implementation should be corrected to use two sockets by default for
++   parallel queries.
++
++   The query stored in BUF of BUFLEN length is sent first followed by
++   the query stored in BUF2 of BUFLEN2 length.  Queries are sent
++   serially on the same socket.
++
++   Answers to the query are stored firstly in *ANSP up to a max of
++   *ANSSIZP bytes.  If more than *ANSSIZP bytes are needed and ANSCP
++   is non-NULL (to indicate that modifying the answer buffer is allowed)
++   then malloc is used to allocate a new response buffer and ANSCP and
++   ANSP will both point to the new buffer.  If more than *ANSSIZP bytes
++   are needed but ANSCP is NULL, then as much of the response as
++   possible is read into the buffer, but the results will be truncated.
++   When truncation happens because of a small answer buffer the DNS
++   packets header field TC will bet set to 1, indicating a truncated
++   message and the rest of the socket data will be read and discarded.
++
++   Answers to the query are stored secondly in *ANSP2 up to a max of
++   *ANSSIZP2 bytes, with the actual response length stored in
++   *RESPLEN2.  If more than *ANSSIZP bytes are needed and ANSP2
++   is non-NULL (required for a second query) then malloc is used to
++   allocate a new response buffer, *ANSSIZP2 is set to the new buffer
++   size and *ANSP2_MALLOCED is set to 1.
++
++   The ANSP2_MALLOCED argument will eventually be removed as the
++   change in buffer pointer can be used to detect the buffer has
++   changed and that the caller should use free on the new buffer.
++
++   Note that the answers may arrive in any order from the server and
++   therefore the first and second answer buffers may not correspond to
++   the first and second queries.
++
++   It is not supported to call this function with a non-NULL ANSP2
++   but a NULL ANSCP.  Put another way, you can call send_vc with a
++   single unmodifiable buffer or two modifiable buffers, but no other
++   combination is supported.
++
++   It is the caller's responsibility to free the malloc allocated
++   buffers by detecting that the pointers have changed from their
++   original values i.e. *ANSCP or *ANSP2 has changed.
++
++   If errors are encountered then *TERRNO is set to an appropriate
++   errno value and a zero result is returned for a recoverable error,
++   and a less-than zero result is returned for a non-recoverable error.
++
++   If no errors are encountered then *TERRNO is left unmodified and
++   a the length of the first response in bytes is returned.  */
+ static int
+ send_vc(res_state statp,
+        const u_char *buf, int buflen, const u_char *buf2, int buflen2,
+@@ -647,11 +737,7 @@ send_vc(res_state statp,
+ {
+        const HEADER *hp = (HEADER *) buf;
+        const HEADER *hp2 = (HEADER *) buf2;
+-       u_char *ans = *ansp;
+-       int orig_anssizp = *anssizp;
+-       // XXX REMOVE
+-       // int anssiz = *anssizp;
+-       HEADER *anhp = (HEADER *) ans;
++       HEADER *anhp = (HEADER *) *ansp;
+        struct sockaddr *nsap = get_nsaddr (statp, ns);
+        int truncating, connreset, n;
+        /* On some architectures compiler might emit a warning indicating
+@@ -743,6 +829,8 @@ send_vc(res_state statp,
+         * Receive length & response
+         */
+        int recvresp1 = 0;
++       /* Skip the second response if there is no second query.
++          To do that we mark the second response as received.  */
+        int recvresp2 = buf2 == NULL;
+        uint16_t rlen16;
+  read_len:
+@@ -779,40 +867,14 @@ send_vc(res_state statp,
+        u_char **thisansp;
+        int *thisresplenp;
+        if ((recvresp1 | recvresp2) == 0 || buf2 == NULL) {
++               /* We have not received any responses
++                  yet or we only have one response to
++                  receive.  */
+                thisanssizp = anssizp;
+                thisansp = anscp ?: ansp;
+                assert (anscp != NULL || ansp2 == NULL);
+                thisresplenp = &resplen;
+        } else {
+-               if (*anssizp != MAXPACKET) {
+-                       /* No buffer allocated for the first
+-                          reply.  We can try to use the rest
+-                          of the user-provided buffer.  */
+-#if __GNUC_PREREQ (4, 7)
+-                       DIAG_PUSH_NEEDS_COMMENT;
+-                       DIAG_IGNORE_NEEDS_COMMENT (5, "-Wmaybe-uninitialized");
+-#endif
+-#if _STRING_ARCH_unaligned
+-                       *anssizp2 = orig_anssizp - resplen;
+-                       *ansp2 = *ansp + resplen;
+-#else
+-                       int aligned_resplen
+-                         = ((resplen + __alignof__ (HEADER) - 1)
+-                            & ~(__alignof__ (HEADER) - 1));
+-                       *anssizp2 = orig_anssizp - aligned_resplen;
+-                       *ansp2 = *ansp + aligned_resplen;
+-#endif
+-#if __GNUC_PREREQ (4, 7)
+-                       DIAG_POP_NEEDS_COMMENT;
+-#endif
+-               } else {
+-                       /* The first reply did not fit into the
+-                          user-provided buffer.  Maybe the second
+-                          answer will.  */
+-                       *anssizp2 = orig_anssizp;
+-                       *ansp2 = *ansp;
+-               }
+-
+                thisanssizp = anssizp2;
+                thisansp = ansp2;
+                thisresplenp = resplen2;
+@@ -820,10 +882,14 @@ send_vc(res_state statp,
+        anhp = (HEADER *) *thisansp;
+ 
+        *thisresplenp = rlen;
+-       if (rlen > *thisanssizp) {
+-               /* Yes, we test ANSCP here.  If we have two buffers
+-                  both will be allocatable.  */
+-               if (__glibc_likely (anscp != NULL))       {
++       /* Is the answer buffer too small?  */
++       if (*thisanssizp < rlen) {
++               /* If the current buffer is not the the static
++                  user-supplied buffer then we can reallocate
++                  it.  */
++               if (thisansp != NULL && thisansp != ansp) {
++                       /* Always allocate MAXPACKET, callers expect
++                          this specific size.  */
+                        u_char *newp = malloc (MAXPACKET);
+                        if (newp == NULL) {
+                                *terrno = ENOMEM;
+@@ -835,6 +901,9 @@ send_vc(res_state statp,
+                        if (thisansp == ansp2)
+                          *ansp2_malloced = 1;
+                        anhp = (HEADER *) newp;
++                       /* A uint16_t can't be larger than MAXPACKET
++                          thus it's safe to allocate MAXPACKET but
++                          read RLEN bytes instead.  */
+                        len = rlen;
+                } else {
+                        Dprint(statp->options & RES_DEBUG,
+@@ -997,6 +1066,66 @@ reopen (res_state statp, int *terrno, in
+        return 1;
+ }
+ 
++/* The send_dg function is responsible for sending a DNS query over UDP
++   to the nameserver numbered NS from the res_state STATP i.e.
++   EXT(statp).nssocks[ns].  The function supports IPv4 and IPv6 queries
++   along with the ability to send the query in parallel for both stacks
++   (default) or serially (RES_SINGLKUP).  It also supports serial lookup
++   with a close and reopen of the socket used to talk to the server
++   (RES_SNGLKUPREOP) to work around broken name servers.
++
++   The query stored in BUF of BUFLEN length is sent first followed by
++   the query stored in BUF2 of BUFLEN2 length.  Queries are sent
++   in parallel (default) or serially (RES_SINGLKUP or RES_SNGLKUPREOP).
++
++   Answers to the query are stored firstly in *ANSP up to a max of
++   *ANSSIZP bytes.  If more than *ANSSIZP bytes are needed and ANSCP
++   is non-NULL (to indicate that modifying the answer buffer is allowed)
++   then malloc is used to allocate a new response buffer and ANSCP and
++   ANSP will both point to the new buffer.  If more than *ANSSIZP bytes
++   are needed but ANSCP is NULL, then as much of the response as
++   possible is read into the buffer, but the results will be truncated.
++   When truncation happens because of a small answer buffer the DNS
++   packets header field TC will bet set to 1, indicating a truncated
++   message, while the rest of the UDP packet is discarded.
++
++   Answers to the query are stored secondly in *ANSP2 up to a max of
++   *ANSSIZP2 bytes, with the actual response length stored in
++   *RESPLEN2.  If more than *ANSSIZP bytes are needed and ANSP2
++   is non-NULL (required for a second query) then malloc is used to
++   allocate a new response buffer, *ANSSIZP2 is set to the new buffer
++   size and *ANSP2_MALLOCED is set to 1.
++
++   The ANSP2_MALLOCED argument will eventually be removed as the
++   change in buffer pointer can be used to detect the buffer has
++   changed and that the caller should use free on the new buffer.
++
++   Note that the answers may arrive in any order from the server and
++   therefore the first and second answer buffers may not correspond to
++   the first and second queries.
++
++   It is not supported to call this function with a non-NULL ANSP2
++   but a NULL ANSCP.  Put another way, you can call send_vc with a
++   single unmodifiable buffer or two modifiable buffers, but no other
++   combination is supported.
++
++   It is the caller's responsibility to free the malloc allocated
++   buffers by detecting that the pointers have changed from their
++   original values i.e. *ANSCP or *ANSP2 has changed.
++
++   If an answer is truncated because of UDP datagram DNS limits then
++   *V_CIRCUIT is set to 1 and the return value non-zero to indicate to
++   the caller to retry with TCP.  The value *GOTSOMEWHERE is set to 1
++   if any progress was made reading a response from the nameserver and
++   is used by the caller to distinguish between ECONNREFUSED and
++   ETIMEDOUT (the latter if *GOTSOMEWHERE is 1).
++
++   If errors are encountered then *TERRNO is set to an appropriate
++   errno value and a zero result is returned for a recoverable error,
++   and a less-than zero result is returned for a non-recoverable error.
++
++   If no errors are encountered then *TERRNO is left unmodified and
++   a the length of the first response in bytes is returned.  */
+ static int
+ send_dg(res_state statp,
+        const u_char *buf, int buflen, const u_char *buf2, int buflen2,
+@@ -1006,8 +1135,6 @@ send_dg(res_state statp,
+ {
+        const HEADER *hp = (HEADER *) buf;
+        const HEADER *hp2 = (HEADER *) buf2;
+-       u_char *ans = *ansp;
+-       int orig_anssizp = *anssizp;
+        struct timespec now, timeout, finish;
+        struct pollfd pfd[1];
+        int ptimeout;
+@@ -1040,6 +1167,8 @@ send_dg(res_state statp,
+        int need_recompute = 0;
+        int nwritten = 0;
+        int recvresp1 = 0;
++       /* Skip the second response if there is no second query.
++          To do that we mark the second response as received.  */
+        int recvresp2 = buf2 == NULL;
+        pfd[0].fd = EXT(statp).nssocks[ns];
+        pfd[0].events = POLLOUT;
+@@ -1203,55 +1332,56 @@ send_dg(res_state statp,
+                int *thisresplenp;
+ 
+                if ((recvresp1 | recvresp2) == 0 || buf2 == NULL) {
++                       /* We have not received any responses
++                          yet or we only have one response to
++                          receive.  */
+                        thisanssizp = anssizp;
+                        thisansp = anscp ?: ansp;
+                        assert (anscp != NULL || ansp2 == NULL);
+                        thisresplenp = &resplen;
+                } else {
+-                       if (*anssizp != MAXPACKET) {
+-                               /* No buffer allocated for the first
+-                                  reply.  We can try to use the rest
+-                                  of the user-provided buffer.  */
+-#if _STRING_ARCH_unaligned
+-                               *anssizp2 = orig_anssizp - resplen;
+-                               *ansp2 = *ansp + resplen;
+-#else
+-                               int aligned_resplen
+-                                 = ((resplen + __alignof__ (HEADER) - 1)
+-                                    & ~(__alignof__ (HEADER) - 1));
+-                               *anssizp2 = orig_anssizp - aligned_resplen;
+-                               *ansp2 = *ansp + aligned_resplen;
+-#endif
+-                       } else {
+-                               /* The first reply did not fit into the
+-                                  user-provided buffer.  Maybe the second
+-                                  answer will.  */
+-                               *anssizp2 = orig_anssizp;
+-                               *ansp2 = *ansp;
+-                       }
+-
+                        thisanssizp = anssizp2;
+                        thisansp = ansp2;
+                        thisresplenp = resplen2;
+                }
+ 
+                if (*thisanssizp < MAXPACKET
+-                   /* Yes, we test ANSCP here.  If we have two buffers
+-                      both will be allocatable.  */
+-                   && anscp
++                   /* If the current buffer is not the the static
++                      user-supplied buffer then we can reallocate
++                      it.  */
++                   && (thisansp != NULL && thisansp != ansp)
+ #ifdef FIONREAD
++                   /* Is the size too small?  */
+                    && (ioctl (pfd[0].fd, FIONREAD, thisresplenp) < 0
+                        || *thisanssizp < *thisresplenp)
+ #endif
+                     ) {
++                       /* Always allocate MAXPACKET, callers expect
++                          this specific size.  */
+                        u_char *newp = malloc (MAXPACKET);
+                        if (newp != NULL) {
+-                               *anssizp = MAXPACKET;
+-                               *thisansp = ans = newp;
++                               *thisanssizp = MAXPACKET;
++                               *thisansp = newp;
+                                if (thisansp == ansp2)
+                                  *ansp2_malloced = 1;
+                        }
+                }
++               /* We could end up with truncation if anscp was NULL
++                  (not allowed to change caller's buffer) and the
++                  response buffer size is too small.  This isn't a
++                  reliable way to detect truncation because the ioctl
++                  may be an inaccurate report of the UDP message size.
++                  Therefore we use this only to issue debug output.
++                  To do truncation accurately with UDP we need
++                  MSG_TRUNC which is only available on Linux.  We
++                  can abstract out the Linux-specific feature in the
++                  future to detect truncation.  */
++               if (__glibc_unlikely (*thisanssizp < *thisresplenp)) {
++                       Dprint(statp->options & RES_DEBUG,
++                              (stdout, ";; response may be truncated (UDP)\n")
++                       );
++               }
++
+                HEADER *anhp = (HEADER *) *thisansp;
+                socklen_t fromlen = sizeof(struct sockaddr_in6);
+                assert (sizeof(from) <= fromlen);
+Index: git/ChangeLog
+===================================================================
+--- git.orig/ChangeLog
++++ git/ChangeLog
+@@ -1,3 +1,18 @@
++2016-02-15  Carlos O'Donell  <carlos@redhat.com>
++
++   [BZ #18665]
++   * resolv/nss_dns/dns-host.c (gaih_getanswer_slice): Always set
++   *herrno_p.
++   (gaih_getanswer): Document functional behviour. Return tryagain
++   if any result is tryagain.
++   * resolv/res_query.c (__libc_res_nsearch): Set buffer size to zero
++   when freed.
++   * resolv/res_send.c: Add copyright text.
++   (__libc_res_nsend): Document that MAXPACKET is expected.
++   (send_vc): Document. Remove buffer reuse.
++   (send_dg): Document. Remove buffer reuse. Set *thisanssizp to set the
++   size of the buffer. Add Dprint for truncated UDP buffer.
++
+ 2015-09-26  Paul Pluzhnikov  <ppluzhnikov@google.com>
+ 
+        [BZ #18985]