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commit 08504de71813ddbd447bfbca4a325cbe8ce8bcda
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Author: Florian Weimer <fweimer@redhat.com>
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Date: Tue Mar 12 11:40:47 2019 +0100
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resolv: Enable full ICMP errors for UDP DNS sockets [BZ #24047]
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The Linux kernel suppresses some ICMP error messages by default for
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UDP sockets. This commit enables full ICMP error reporting,
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hopefully resulting in faster failover to working name servers.
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diff --git a/resolv/Makefile b/resolv/Makefile
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index 8f22e6a154..ebe1b733f2 100644
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--- a/resolv/Makefile
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+++ b/resolv/Makefile
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@@ -105,7 +105,7 @@ libresolv-routines := res_comp res_debug \
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res_data res_mkquery res_query res_send \
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inet_net_ntop inet_net_pton inet_neta base64 \
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ns_parse ns_name ns_netint ns_ttl ns_print \
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- ns_samedomain ns_date \
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+ ns_samedomain ns_date res_enable_icmp \
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compat-hooks compat-gethnamaddr
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libanl-routines := gai_cancel gai_error gai_misc gai_notify gai_suspend \
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diff --git a/resolv/res_enable_icmp.c b/resolv/res_enable_icmp.c
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new file mode 100644
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index 0000000000..bdc9220f08
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--- /dev/null
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+++ b/resolv/res_enable_icmp.c
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@@ -0,0 +1,37 @@
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+/* Enable full ICMP errors on a socket.
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+ Copyright (C) 2019 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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+#include <errno.h>
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+#include <netinet/in.h>
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+#include <sys/socket.h>
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+
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+int
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+__res_enable_icmp (int family, int fd)
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+{
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+ int one = 1;
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+ switch (family)
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+ {
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+ case AF_INET:
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+ return setsockopt (fd, SOL_IP, IP_RECVERR, &one, sizeof (one));
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+ case AF_INET6:
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+ return setsockopt (fd, SOL_IPV6, IPV6_RECVERR, &one, sizeof (one));
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+ default:
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+ __set_errno (EAFNOSUPPORT);
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+ return -1;
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+ }
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+}
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diff --git a/resolv/res_send.c b/resolv/res_send.c
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index fa040c1198..0f6ec83a7b 100644
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--- a/resolv/res_send.c
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+++ b/resolv/res_send.c
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@@ -943,6 +943,18 @@ reopen (res_state statp, int *terrno, int ns)
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return (-1);
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}
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+ /* Enable full ICMP error reporting for this
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+ socket. */
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+ if (__res_enable_icmp (nsap->sa_family,
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+ EXT (statp).nssocks[ns]) < 0)
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+ {
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+ int saved_errno = errno;
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+ __res_iclose (statp, false);
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+ __set_errno (saved_errno);
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+ *terrno = saved_errno;
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+ return -1;
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+ }
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+
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/*
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* On a 4.3BSD+ machine (client and server,
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* actually), sending to a nameserver datagram
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diff --git a/resolv/resolv-internal.h b/resolv/resolv-internal.h
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index 6ab8f2af09..1500adc607 100644
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--- a/resolv/resolv-internal.h
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+++ b/resolv/resolv-internal.h
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@@ -100,4 +100,10 @@ libc_hidden_proto (__inet_pton_length)
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/* Called as part of the thread shutdown sequence. */
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void __res_thread_freeres (void) attribute_hidden;
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+/* The Linux kernel does not enable all ICMP messages on a UDP socket
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+ by default. A call this function enables full error reporting for
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+ the socket FD. FAMILY must be AF_INET or AF_INET6. Returns 0 on
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+ success, -1 on failure. */
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+int __res_enable_icmp (int family, int fd) attribute_hidden;
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+
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#endif /* _RESOLV_INTERNAL_H */
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