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@@ -0,0 +1,585 @@
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+From: Carlos O'Donell <carlos@systemhalted.org>
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+Date: Tue, 16 Feb 2016 21:26:37 -0500
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+Subject: [PATCH] CVE-2015-7547: getaddrinfo() stack-based buffer overflow (Bug
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+ 18665).
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+
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+* A stack-based buffer overflow was found in libresolv when invoked from
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+ libnss_dns, allowing specially crafted DNS responses to seize control
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+ of execution flow in the DNS client. The buffer overflow occurs in
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+ the functions send_dg (send datagram) and send_vc (send TCP) for the
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+ NSS module libnss_dns.so.2 when calling getaddrinfo with AF_UNSPEC
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+ family. The use of AF_UNSPEC triggers the low-level resolver code to
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+ send out two parallel queries for A and AAAA. A mismanagement of the
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+ buffers used for those queries could result in the response of a query
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+ writing beyond the alloca allocated buffer created by
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+ _nss_dns_gethostbyname4_r. Buffer management is simplified to remove
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+ the overflow. Thanks to the Google Security Team and Red Hat for
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+ reporting the security impact of this issue, and Robert Holiday of
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+ Ciena for reporting the related bug 18665. (CVE-2015-7547)
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+
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+See also:
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+https://sourceware.org/ml/libc-alpha/2016-02/msg00416.html
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+https://sourceware.org/ml/libc-alpha/2016-02/msg00418.html
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+
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+Upstream-Status: Backport
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+CVE: CVE-2015-7547
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+
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+Upstream commit:
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+https://sourceware.org/git/?p=glibc.git;a=commit;h=16d0a0ce7613552301786bf05d7eba8784b5732c
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+
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+Tweaks:
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+* Adapted from GLIBC-2.20 to EGLIBC-2.19
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+* Removed changes to ChangeLog and NEWS files
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+
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+Signed-off-by: Javier Viguera <javier.viguera@digi.com>
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+---
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+ resolv/nss_dns/dns-host.c | 111 +++++++++++++++++++-
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+ resolv/res_query.c | 3 +
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+ resolv/res_send.c | 257 +++++++++++++++++++++++++++++++++++-----------
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+ 3 files changed, 309 insertions(+), 62 deletions(-)
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+
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+diff --git a/resolv/nss_dns/dns-host.c b/resolv/nss_dns/dns-host.c
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+index f8f192e5afb5..e7e2c7137a50 100644
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+--- a/resolv/nss_dns/dns-host.c
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++++ b/resolv/nss_dns/dns-host.c
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+@@ -1049,7 +1049,10 @@ gaih_getanswer_slice (const querybuf *answer, int anslen, const char *qname,
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+ int h_namelen = 0;
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+
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+ if (ancount == 0)
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+- return NSS_STATUS_NOTFOUND;
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++ {
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++ *h_errnop = HOST_NOT_FOUND;
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++ return NSS_STATUS_NOTFOUND;
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++ }
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+
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+ while (ancount-- > 0 && cp < end_of_message && had_error == 0)
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+ {
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+@@ -1226,7 +1229,14 @@ gaih_getanswer_slice (const querybuf *answer, int anslen, const char *qname,
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+ /* Special case here: if the resolver sent a result but it only
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+ contains a CNAME while we are looking for a T_A or T_AAAA record,
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+ we fail with NOTFOUND instead of TRYAGAIN. */
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+- return canon == NULL ? NSS_STATUS_TRYAGAIN : NSS_STATUS_NOTFOUND;
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++ if (canon != NULL)
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++ {
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++ *h_errnop = HOST_NOT_FOUND;
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++ return NSS_STATUS_NOTFOUND;
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++ }
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++
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++ *h_errnop = NETDB_INTERNAL;
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++ return NSS_STATUS_TRYAGAIN;
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+ }
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+
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+
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+@@ -1240,11 +1250,101 @@ gaih_getanswer (const querybuf *answer1, int anslen1, const querybuf *answer2,
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+
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+ enum nss_status status = NSS_STATUS_NOTFOUND;
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+
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++ /* Combining the NSS status of two distinct queries requires some
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++ compromise and attention to symmetry (A or AAAA queries can be
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++ returned in any order). What follows is a breakdown of how this
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++ code is expected to work and why. We discuss only SUCCESS,
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++ TRYAGAIN, NOTFOUND and UNAVAIL, since they are the only returns
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++ that apply (though RETURN and MERGE exist). We make a distinction
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++ between TRYAGAIN (recoverable) and TRYAGAIN' (not-recoverable).
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++ A recoverable TRYAGAIN is almost always due to buffer size issues
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++ and returns ERANGE in errno and the caller is expected to retry
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++ with a larger buffer.
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++
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++ Lastly, you may be tempted to make significant changes to the
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++ conditions in this code to bring about symmetry between responses.
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++ Please don't change anything without due consideration for
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++ expected application behaviour. Some of the synthesized responses
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++ aren't very well thought out and sometimes appear to imply that
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++ IPv4 responses are always answer 1, and IPv6 responses are always
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++ answer 2, but that's not true (see the implementation of send_dg
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++ and send_vc to see response can arrive in any order, particularly
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++ for UDP). However, we expect it holds roughly enough of the time
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++ that this code works, but certainly needs to be fixed to make this
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++ a more robust implementation.
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++
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++ ----------------------------------------------
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++ | Answer 1 Status / | Synthesized | Reason |
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++ | Answer 2 Status | Status | |
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++ |--------------------------------------------|
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++ | SUCCESS/SUCCESS | SUCCESS | [1] |
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++ | SUCCESS/TRYAGAIN | TRYAGAIN | [5] |
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++ | SUCCESS/TRYAGAIN' | SUCCESS | [1] |
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++ | SUCCESS/NOTFOUND | SUCCESS | [1] |
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++ | SUCCESS/UNAVAIL | SUCCESS | [1] |
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++ | TRYAGAIN/SUCCESS | TRYAGAIN | [2] |
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++ | TRYAGAIN/TRYAGAIN | TRYAGAIN | [2] |
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++ | TRYAGAIN/TRYAGAIN' | TRYAGAIN | [2] |
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++ | TRYAGAIN/NOTFOUND | TRYAGAIN | [2] |
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++ | TRYAGAIN/UNAVAIL | TRYAGAIN | [2] |
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++ | TRYAGAIN'/SUCCESS | SUCCESS | [3] |
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++ | TRYAGAIN'/TRYAGAIN | TRYAGAIN | [3] |
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++ | TRYAGAIN'/TRYAGAIN' | TRYAGAIN' | [3] |
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++ | TRYAGAIN'/NOTFOUND | TRYAGAIN' | [3] |
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++ | TRYAGAIN'/UNAVAIL | UNAVAIL | [3] |
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++ | NOTFOUND/SUCCESS | SUCCESS | [3] |
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++ | NOTFOUND/TRYAGAIN | TRYAGAIN | [3] |
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++ | NOTFOUND/TRYAGAIN' | TRYAGAIN' | [3] |
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++ | NOTFOUND/NOTFOUND | NOTFOUND | [3] |
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++ | NOTFOUND/UNAVAIL | UNAVAIL | [3] |
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++ | UNAVAIL/SUCCESS | UNAVAIL | [4] |
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++ | UNAVAIL/TRYAGAIN | UNAVAIL | [4] |
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++ | UNAVAIL/TRYAGAIN' | UNAVAIL | [4] |
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++ | UNAVAIL/NOTFOUND | UNAVAIL | [4] |
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++ | UNAVAIL/UNAVAIL | UNAVAIL | [4] |
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++ ----------------------------------------------
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++
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++ [1] If the first response is a success we return success.
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++ This ignores the state of the second answer and in fact
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++ incorrectly sets errno and h_errno to that of the second
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++ answer. However because the response is a success we ignore
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++ *errnop and *h_errnop (though that means you touched errno on
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++ success). We are being conservative here and returning the
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++ likely IPv4 response in the first answer as a success.
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++
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++ [2] If the first response is a recoverable TRYAGAIN we return
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++ that instead of looking at the second response. The
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++ expectation here is that we have failed to get an IPv4 response
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++ and should retry both queries.
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++
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++ [3] If the first response was not a SUCCESS and the second
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++ response is not NOTFOUND (had a SUCCESS, need to TRYAGAIN,
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++ or failed entirely e.g. TRYAGAIN' and UNAVAIL) then use the
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++ result from the second response, otherwise the first responses
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++ status is used. Again we have some odd side-effects when the
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++ second response is NOTFOUND because we overwrite *errnop and
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++ *h_errnop that means that a first answer of NOTFOUND might see
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++ its *errnop and *h_errnop values altered. Whether it matters
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++ in practice that a first response NOTFOUND has the wrong
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++ *errnop and *h_errnop is undecided.
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++
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++ [4] If the first response is UNAVAIL we return that instead of
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++ looking at the second response. The expectation here is that
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++ it will have failed similarly e.g. configuration failure.
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++
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++ [5] Testing this code is complicated by the fact that truncated
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++ second response buffers might be returned as SUCCESS if the
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++ first answer is a SUCCESS. To fix this we add symmetry to
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++ TRYAGAIN with the second response. If the second response
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++ is a recoverable error we now return TRYAGIN even if the first
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++ response was SUCCESS. */
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++
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+ if (anslen1 > 0)
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+ status = gaih_getanswer_slice(answer1, anslen1, qname,
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+ &pat, &buffer, &buflen,
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+ errnop, h_errnop, ttlp,
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+ &first);
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++
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+ if ((status == NSS_STATUS_SUCCESS || status == NSS_STATUS_NOTFOUND
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+ || (status == NSS_STATUS_TRYAGAIN
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+ /* We want to look at the second answer in case of an
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+@@ -1260,8 +1360,15 @@ gaih_getanswer (const querybuf *answer1, int anslen1, const querybuf *answer2,
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+ &pat, &buffer, &buflen,
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+ errnop, h_errnop, ttlp,
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+ &first);
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++ /* Use the second response status in some cases. */
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+ if (status != NSS_STATUS_SUCCESS && status2 != NSS_STATUS_NOTFOUND)
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+ status = status2;
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++ /* Do not return a truncated second response (unless it was
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++ unavoidable e.g. unrecoverable TRYAGAIN). */
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++ if (status == NSS_STATUS_SUCCESS
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++ && (status2 == NSS_STATUS_TRYAGAIN
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++ && *errnop == ERANGE && *h_errnop != NO_RECOVERY))
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++ status = NSS_STATUS_TRYAGAIN;
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+ }
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+
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+ return status;
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+diff --git a/resolv/res_query.c b/resolv/res_query.c
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+index 1325f9772ddc..dd87e097c461 100644
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+--- a/resolv/res_query.c
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++++ b/resolv/res_query.c
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+@@ -391,6 +391,7 @@ __libc_res_nsearch(res_state statp,
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+ {
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+ free (*answerp2);
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+ *answerp2 = NULL;
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++ *nanswerp2 = 0;
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+ }
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+ }
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+
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+@@ -431,6 +432,7 @@ __libc_res_nsearch(res_state statp,
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+ {
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+ free (*answerp2);
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+ *answerp2 = NULL;
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++ *nanswerp2 = 0;
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+ }
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+
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+ /*
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+@@ -502,6 +504,7 @@ __libc_res_nsearch(res_state statp,
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+ {
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+ free (*answerp2);
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+ *answerp2 = NULL;
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++ *nanswerp2 = 0;
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+ }
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+ if (saved_herrno != -1)
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+ RES_SET_H_ERRNO(statp, saved_herrno);
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+diff --git a/resolv/res_send.c b/resolv/res_send.c
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+index 7f2e85f3240e..5940b0c7ebf7 100644
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+--- a/resolv/res_send.c
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++++ b/resolv/res_send.c
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+@@ -1,3 +1,20 @@
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++/* Copyright (C) 2016 Free Software Foundation, Inc.
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++ This file is part of the GNU C Library.
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++
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++ The GNU C Library is free software; you can redistribute it and/or
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++ modify it under the terms of the GNU Lesser General Public
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++ License as published by the Free Software Foundation; either
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++ version 2.1 of the License, or (at your option) any later version.
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++
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++ The GNU C Library is distributed in the hope that it will be useful,
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++ but WITHOUT ANY WARRANTY; without even the implied warranty of
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++ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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++ Lesser General Public License for more details.
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++
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++ You should have received a copy of the GNU Lesser General Public
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++ License along with the GNU C Library; if not, see
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++ <http://www.gnu.org/licenses/>. */
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++
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+ /*
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+ * Copyright (c) 1985, 1989, 1993
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+ * The Regents of the University of California. All rights reserved.
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+@@ -360,6 +377,8 @@ __libc_res_nsend(res_state statp, const u_char *buf, int buflen,
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+ #ifdef USE_HOOKS
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+ if (__builtin_expect (statp->qhook || statp->rhook, 0)) {
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+ if (anssiz < MAXPACKET && ansp) {
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++ /* Always allocate MAXPACKET, callers expect
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++ this specific size. */
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+ u_char *buf = malloc (MAXPACKET);
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+ if (buf == NULL)
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+ return (-1);
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+@@ -652,6 +671,77 @@ libresolv_hidden_def (res_nsend)
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+
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+ /* Private */
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+
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++/* The send_vc function is responsible for sending a DNS query over TCP
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++ to the nameserver numbered NS from the res_state STATP i.e.
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++ EXT(statp).nssocks[ns]. The function supports sending both IPv4 and
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++ IPv6 queries at the same serially on the same socket.
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++
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++ Please note that for TCP there is no way to disable sending both
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++ queries, unlike UDP, which honours RES_SNGLKUP and RES_SNGLKUPREOP
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++ and sends the queries serially and waits for the result after each
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++ sent query. This implemetnation should be corrected to honour these
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++ options.
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++
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++ Please also note that for TCP we send both queries over the same
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++ socket one after another. This technically violates best practice
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++ since the server is allowed to read the first query, respond, and
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++ then close the socket (to service another client). If the server
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++ does this, then the remaining second query in the socket data buffer
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++ will cause the server to send the client an RST which will arrive
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++ asynchronously and the client's OS will likely tear down the socket
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++ receive buffer resulting in a potentially short read and lost
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++ response data. This will force the client to retry the query again,
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++ and this process may repeat until all servers and connection resets
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++ are exhausted and then the query will fail. It's not known if this
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++ happens with any frequency in real DNS server implementations. This
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++ implementation should be corrected to use two sockets by default for
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++ parallel queries.
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++
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++ The query stored in BUF of BUFLEN length is sent first followed by
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++ the query stored in BUF2 of BUFLEN2 length. Queries are sent
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++ serially on the same socket.
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++
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++ Answers to the query are stored firstly in *ANSP up to a max of
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++ *ANSSIZP bytes. If more than *ANSSIZP bytes are needed and ANSCP
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++ is non-NULL (to indicate that modifying the answer buffer is allowed)
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++ then malloc is used to allocate a new response buffer and ANSCP and
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++ ANSP will both point to the new buffer. If more than *ANSSIZP bytes
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++ are needed but ANSCP is NULL, then as much of the response as
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++ possible is read into the buffer, but the results will be truncated.
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++ When truncation happens because of a small answer buffer the DNS
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++ packets header field TC will bet set to 1, indicating a truncated
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++ message and the rest of the socket data will be read and discarded.
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++
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++ Answers to the query are stored secondly in *ANSP2 up to a max of
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++ *ANSSIZP2 bytes, with the actual response length stored in
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++ *RESPLEN2. If more than *ANSSIZP bytes are needed and ANSP2
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++ is non-NULL (required for a second query) then malloc is used to
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++ allocate a new response buffer, *ANSSIZP2 is set to the new buffer
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++ size and *ANSP2_MALLOCED is set to 1.
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++
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++ The ANSP2_MALLOCED argument will eventually be removed as the
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++ change in buffer pointer can be used to detect the buffer has
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++ changed and that the caller should use free on the new buffer.
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++
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++ Note that the answers may arrive in any order from the server and
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++ therefore the first and second answer buffers may not correspond to
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++ the first and second queries.
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++
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++ It is not supported to call this function with a non-NULL ANSP2
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++ but a NULL ANSCP. Put another way, you can call send_vc with a
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++ single unmodifiable buffer or two modifiable buffers, but no other
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++ combination is supported.
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++
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++ It is the caller's responsibility to free the malloc allocated
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++ buffers by detecting that the pointers have changed from their
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++ original values i.e. *ANSCP or *ANSP2 has changed.
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++
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++ If errors are encountered then *TERRNO is set to an appropriate
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++ errno value and a zero result is returned for a recoverable error,
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++ and a less-than zero result is returned for a non-recoverable error.
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++
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++ If no errors are encountered then *TERRNO is left unmodified and
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++ a the length of the first response in bytes is returned. */
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+ static int
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+ send_vc(res_state statp,
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+ const u_char *buf, int buflen, const u_char *buf2, int buflen2,
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+@@ -661,11 +751,7 @@ send_vc(res_state statp,
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+ {
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+ const HEADER *hp = (HEADER *) buf;
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+ const HEADER *hp2 = (HEADER *) buf2;
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+- u_char *ans = *ansp;
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+- int orig_anssizp = *anssizp;
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+- // XXX REMOVE
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+- // int anssiz = *anssizp;
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+- HEADER *anhp = (HEADER *) ans;
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++ HEADER *anhp = (HEADER *) *ansp;
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+ struct sockaddr_in6 *nsap = EXT(statp).nsaddrs[ns];
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+ int truncating, connreset, resplen, n;
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+ struct iovec iov[4];
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+@@ -741,6 +827,8 @@ send_vc(res_state statp,
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+ * Receive length & response
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+ */
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+ int recvresp1 = 0;
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++ /* Skip the second response if there is no second query.
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++ To do that we mark the second response as received. */
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+ int recvresp2 = buf2 == NULL;
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+ uint16_t rlen16;
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+ read_len:
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+@@ -777,33 +865,14 @@ send_vc(res_state statp,
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+ u_char **thisansp;
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+ int *thisresplenp;
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+ if ((recvresp1 | recvresp2) == 0 || buf2 == NULL) {
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++ /* We have not received any responses
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++ yet or we only have one response to
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++ receive. */
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+ thisanssizp = anssizp;
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+ thisansp = anscp ?: ansp;
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+ assert (anscp != NULL || ansp2 == NULL);
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+ thisresplenp = &resplen;
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+ } else {
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+- if (*anssizp != MAXPACKET) {
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+- /* No buffer allocated for the first
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+- reply. We can try to use the rest
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+- of the user-provided buffer. */
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+-#ifdef _STRING_ARCH_unaligned
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+- *anssizp2 = orig_anssizp - resplen;
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+- *ansp2 = *ansp + resplen;
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+-#else
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+- int aligned_resplen
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+- = ((resplen + __alignof__ (HEADER) - 1)
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+- & ~(__alignof__ (HEADER) - 1));
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+- *anssizp2 = orig_anssizp - aligned_resplen;
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+- *ansp2 = *ansp + aligned_resplen;
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+-#endif
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+- } else {
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+- /* The first reply did not fit into the
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+- user-provided buffer. Maybe the second
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+- answer will. */
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+- *anssizp2 = orig_anssizp;
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+- *ansp2 = *ansp;
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+- }
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+-
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+ thisanssizp = anssizp2;
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+ thisansp = ansp2;
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+ thisresplenp = resplen2;
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+@@ -811,10 +880,14 @@ send_vc(res_state statp,
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+ anhp = (HEADER *) *thisansp;
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+
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+ *thisresplenp = rlen;
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+- if (rlen > *thisanssizp) {
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+- /* Yes, we test ANSCP here. If we have two buffers
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+- both will be allocatable. */
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+- if (__builtin_expect (anscp != NULL, 1)) {
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++ /* Is the answer buffer too small? */
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++ if (*thisanssizp < rlen) {
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++ /* If the current buffer is not the the static
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++ user-supplied buffer then we can reallocate
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++ it. */
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++ if (thisansp != NULL && thisansp != ansp) {
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++ /* Always allocate MAXPACKET, callers expect
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++ this specific size. */
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+ u_char *newp = malloc (MAXPACKET);
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+ if (newp == NULL) {
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+ *terrno = ENOMEM;
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+@@ -824,6 +897,9 @@ send_vc(res_state statp,
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+ *thisanssizp = MAXPACKET;
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+ *thisansp = newp;
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+ anhp = (HEADER *) newp;
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++ /* A uint16_t can't be larger than MAXPACKET
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++ thus it's safe to allocate MAXPACKET but
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++ read RLEN bytes instead. */
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+ len = rlen;
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+ } else {
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+ Dprint(statp->options & RES_DEBUG,
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+@@ -987,6 +1063,66 @@ reopen (res_state statp, int *terrno, int ns)
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+ return 1;
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+ }
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+
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++/* The send_dg function is responsible for sending a DNS query over UDP
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++ to the nameserver numbered NS from the res_state STATP i.e.
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++ EXT(statp).nssocks[ns]. The function supports IPv4 and IPv6 queries
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++ along with the ability to send the query in parallel for both stacks
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++ (default) or serially (RES_SINGLKUP). It also supports serial lookup
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++ with a close and reopen of the socket used to talk to the server
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++ (RES_SNGLKUPREOP) to work around broken name servers.
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++
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++ The query stored in BUF of BUFLEN length is sent first followed by
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++ the query stored in BUF2 of BUFLEN2 length. Queries are sent
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++ in parallel (default) or serially (RES_SINGLKUP or RES_SNGLKUPREOP).
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++
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++ Answers to the query are stored firstly in *ANSP up to a max of
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++ *ANSSIZP bytes. If more than *ANSSIZP bytes are needed and ANSCP
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++ is non-NULL (to indicate that modifying the answer buffer is allowed)
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++ then malloc is used to allocate a new response buffer and ANSCP and
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++ ANSP will both point to the new buffer. If more than *ANSSIZP bytes
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++ are needed but ANSCP is NULL, then as much of the response as
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++ possible is read into the buffer, but the results will be truncated.
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++ When truncation happens because of a small answer buffer the DNS
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++ packets header field TC will bet set to 1, indicating a truncated
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++ message, while the rest of the UDP packet is discarded.
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++
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++ Answers to the query are stored secondly in *ANSP2 up to a max of
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++ *ANSSIZP2 bytes, with the actual response length stored in
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++ *RESPLEN2. If more than *ANSSIZP bytes are needed and ANSP2
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++ is non-NULL (required for a second query) then malloc is used to
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++ allocate a new response buffer, *ANSSIZP2 is set to the new buffer
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++ size and *ANSP2_MALLOCED is set to 1.
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++
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++ The ANSP2_MALLOCED argument will eventually be removed as the
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++ change in buffer pointer can be used to detect the buffer has
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++ changed and that the caller should use free on the new buffer.
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++
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++ Note that the answers may arrive in any order from the server and
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++ therefore the first and second answer buffers may not correspond to
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++ the first and second queries.
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++
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++ It is not supported to call this function with a non-NULL ANSP2
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++ but a NULL ANSCP. Put another way, you can call send_vc with a
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++ single unmodifiable buffer or two modifiable buffers, but no other
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++ combination is supported.
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++
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++ It is the caller's responsibility to free the malloc allocated
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++ buffers by detecting that the pointers have changed from their
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++ original values i.e. *ANSCP or *ANSP2 has changed.
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++
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++ If an answer is truncated because of UDP datagram DNS limits then
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++ *V_CIRCUIT is set to 1 and the return value non-zero to indicate to
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++ the caller to retry with TCP. The value *GOTSOMEWHERE is set to 1
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++ if any progress was made reading a response from the nameserver and
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++ is used by the caller to distinguish between ECONNREFUSED and
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++ ETIMEDOUT (the latter if *GOTSOMEWHERE is 1).
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++
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++ If errors are encountered then *TERRNO is set to an appropriate
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++ errno value and a zero result is returned for a recoverable error,
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++ and a less-than zero result is returned for a non-recoverable error.
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++
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++ If no errors are encountered then *TERRNO is left unmodified and
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++ a the length of the first response in bytes is returned. */
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+ static int
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+ send_dg(res_state statp,
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+ const u_char *buf, int buflen, const u_char *buf2, int buflen2,
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+@@ -996,8 +1132,6 @@ send_dg(res_state statp,
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+ {
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+ const HEADER *hp = (HEADER *) buf;
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+ const HEADER *hp2 = (HEADER *) buf2;
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+- u_char *ans = *ansp;
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+- int orig_anssizp = *anssizp;
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+ struct timespec now, timeout, finish;
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+ struct pollfd pfd[1];
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+ int ptimeout;
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+@@ -1030,6 +1164,8 @@ send_dg(res_state statp,
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+ int need_recompute = 0;
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+ int nwritten = 0;
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+ int recvresp1 = 0;
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++ /* Skip the second response if there is no second query.
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++ To do that we mark the second response as received. */
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+ int recvresp2 = buf2 == NULL;
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+ pfd[0].fd = EXT(statp).nssocks[ns];
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+ pfd[0].events = POLLOUT;
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+@@ -1193,53 +1329,54 @@ send_dg(res_state statp,
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+ int *thisresplenp;
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+
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+ if ((recvresp1 | recvresp2) == 0 || buf2 == NULL) {
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++ /* We have not received any responses
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++ yet or we only have one response to
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++ receive. */
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+ thisanssizp = anssizp;
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+ thisansp = anscp ?: ansp;
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+ assert (anscp != NULL || ansp2 == NULL);
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+ thisresplenp = &resplen;
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+ } else {
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+- if (*anssizp != MAXPACKET) {
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+- /* No buffer allocated for the first
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+- reply. We can try to use the rest
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+- of the user-provided buffer. */
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+-#ifdef _STRING_ARCH_unaligned
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+- *anssizp2 = orig_anssizp - resplen;
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+- *ansp2 = *ansp + resplen;
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+-#else
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+- int aligned_resplen
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+- = ((resplen + __alignof__ (HEADER) - 1)
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+- & ~(__alignof__ (HEADER) - 1));
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+- *anssizp2 = orig_anssizp - aligned_resplen;
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+- *ansp2 = *ansp + aligned_resplen;
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+-#endif
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+- } else {
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+- /* The first reply did not fit into the
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+- user-provided buffer. Maybe the second
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+- answer will. */
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+- *anssizp2 = orig_anssizp;
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+- *ansp2 = *ansp;
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+- }
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+-
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+ thisanssizp = anssizp2;
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+ thisansp = ansp2;
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+ thisresplenp = resplen2;
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+ }
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+
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+ if (*thisanssizp < MAXPACKET
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+- /* Yes, we test ANSCP here. If we have two buffers
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+- both will be allocatable. */
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+- && anscp
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++ /* If the current buffer is not the the static
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++ user-supplied buffer then we can reallocate
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++ it. */
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++ && (thisansp != NULL && thisansp != ansp)
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+ #ifdef FIONREAD
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++ /* Is the size too small? */
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+ && (ioctl (pfd[0].fd, FIONREAD, thisresplenp) < 0
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+ || *thisanssizp < *thisresplenp)
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+ #endif
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+ ) {
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++ /* Always allocate MAXPACKET, callers expect
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++ this specific size. */
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+ u_char *newp = malloc (MAXPACKET);
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+ if (newp != NULL) {
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+- *anssizp = MAXPACKET;
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+- *thisansp = ans = newp;
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++ *thisanssizp = MAXPACKET;
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++ *thisansp = newp;
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+ }
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+ }
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++ /* We could end up with truncation if anscp was NULL
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++ (not allowed to change caller's buffer) and the
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++ response buffer size is too small. This isn't a
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++ reliable way to detect truncation because the ioctl
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++ may be an inaccurate report of the UDP message size.
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++ Therefore we use this only to issue debug output.
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++ To do truncation accurately with UDP we need
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++ MSG_TRUNC which is only available on Linux. We
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++ can abstract out the Linux-specific feature in the
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++ future to detect truncation. */
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++ if (__glibc_unlikely (*thisanssizp < *thisresplenp)) {
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++ Dprint(statp->options & RES_DEBUG,
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++ (stdout, ";; response may be truncated (UDP)\n")
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++ );
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++ }
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++
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+ HEADER *anhp = (HEADER *) *thisansp;
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+ socklen_t fromlen = sizeof(struct sockaddr_in6);
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+ assert (sizeof(from) <= fromlen);
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