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01/01: gnu: glibc: Add fix for CVE-2015-7547.
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From: |
Mark H. Weaver |
|
Subject: |
01/01: gnu: glibc: Add fix for CVE-2015-7547. |
|
Date: |
Tue, 16 Feb 2016 17:29:57 +0000 |
mhw pushed a commit to branch security-updates
in repository guix.
commit 1d220ea8304ccdbc7b653ab0b81e3cec5420fcc6
Author: Mark H Weaver <address@hidden>
Date: Tue Feb 16 12:13:08 2016 -0500
gnu: glibc: Add fix for CVE-2015-7547.
* gnu/packages/patches/glibc-CVE-2015-7547.patch: New file.
* gnu-system.am (dist_patch_DATA): Add it.
* gnu/packages/base.scm (glibc)[source]: Add patch.
---
gnu-system.am | 1 +
gnu/packages/base.scm | 5 +-
gnu/packages/patches/glibc-CVE-2015-7547.patch | 559 ++++++++++++++++++++++++
3 files changed, 563 insertions(+), 2 deletions(-)
diff --git a/gnu-system.am b/gnu-system.am
index 6c6aa6b..432589e 100644
--- a/gnu-system.am
+++ b/gnu-system.am
@@ -490,6 +490,7 @@ dist_patch_DATA =
\
gnu/packages/patches/glib-tests-prlimit.patch \
gnu/packages/patches/glib-tests-timer.patch \
gnu/packages/patches/glib-tests-gapplication.patch \
+ gnu/packages/patches/glibc-CVE-2015-7547.patch \
gnu/packages/patches/glibc-bootstrap-system.patch \
gnu/packages/patches/glibc-hurd-extern-inline.patch \
gnu/packages/patches/glibc-ldd-x86_64.patch \
diff --git a/gnu/packages/base.scm b/gnu/packages/base.scm
index f8ea80b..7cef8bf 100644
--- a/gnu/packages/base.scm
+++ b/gnu/packages/base.scm
@@ -2,7 +2,7 @@
;;; Copyright © 2012, 2013, 2014, 2015, 2016 Ludovic Courtès <address@hidden>
;;; Copyright © 2014 Andreas Enge <address@hidden>
;;; Copyright © 2012 Nikita Karetnikov <address@hidden>
-;;; Copyright © 2014, 2015 Mark H Weaver <address@hidden>
+;;; Copyright © 2014, 2015, 2016 Mark H Weaver <address@hidden>
;;; Copyright © 2014 Alex Kost <address@hidden>
;;; Copyright © 2014, 2015 Manolis Fragkiskos Ragkousis <address@hidden>
;;; Copyright © 2016 Efraim Flashner <address@hidden>
@@ -488,7 +488,8 @@ store.")
'("glibc-ldd-x86_64.patch"
"glibc-locale-incompatibility.patch"
"glibc-versioned-locpath.patch"
- "glibc-o-largefile.patch")))))
+ "glibc-o-largefile.patch"
+ "glibc-CVE-2015-7547.patch")))))
(build-system gnu-build-system)
;; Glibc's <limits.h> refers to <linux/limit.h>, for instance, so glibc
diff --git a/gnu/packages/patches/glibc-CVE-2015-7547.patch
b/gnu/packages/patches/glibc-CVE-2015-7547.patch
new file mode 100644
index 0000000..9a0909a
--- /dev/null
+++ b/gnu/packages/patches/glibc-CVE-2015-7547.patch
@@ -0,0 +1,559 @@
+Copied from Fedora:
+http://pkgs.fedoraproject.org/cgit/rpms/glibc.git/tree/glibc-CVE-2015-7547.patch?h=f23&id=9f1734eb6ce3257b788d6e9203572e8204c6c584
+
+Adapted to apply cleanly to glibc-2.22.
+
+Index: b/resolv/nss_dns/dns-host.c
+===================================================================
+--- a/resolv/nss_dns/dns-host.c
++++ b/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 implemetnation of send_dg
++ and send_vc to see response can arrive in any order, particlarly
++ 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: b/resolv/res_query.c
+===================================================================
+--- a/resolv/res_query.c
++++ b/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: b/resolv/res_send.c
+===================================================================
+--- a/resolv/res_send.c
++++ b/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.
+@@ -361,6 +378,8 @@ __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);
+@@ -660,6 +679,77 @@ libresolv_hidden_def (res_nsend)
+
+ /* Private */
+
++/* 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 feild 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,
+@@ -669,11 +759,7 @@ 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
+@@ -766,6 +852,8 @@ 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:
+@@ -802,40 +890,14 @@ 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;
+@@ -843,10 +905,14 @@ 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 non-NULL and it's not
++ pointing at 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;
+@@ -858,6 +924,9 @@ 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,
+@@ -1021,6 +1090,66 @@ 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 feild 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,
+@@ -1030,8 +1159,6 @@ 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;
+@@ -1064,6 +1191,8 @@ 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;
+@@ -1227,55 +1356,56 @@ 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 non-NULL and it's not
++ pointing at 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);