279 lines
8.3 KiB
Diff
279 lines
8.3 KiB
Diff
From 291f738f341a78f8c7974a7603d1a2eaa01ebacc Mon Sep 17 00:00:00 2001
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From: Pavel Zhukov <pzhukov@redhat.com>
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Date: Thu, 21 Feb 2019 10:30:28 +0100
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Subject: [PATCH 11/21] Drop unnecessary capabilities
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Cc: pzhukov@redhat.com
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dhclient (#517649, #546765), dhcpd/dhcrelay (#699713)
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---
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client/Makefile.am | 3 ++-
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client/dhclient-script.8 | 10 ++++++++++
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client/dhclient.8 | 29 +++++++++++++++++++++++++++++
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client/dhclient.c | 24 ++++++++++++++++++++++++
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configure.ac | 35 +++++++++++++++++++++++++++++++++++
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relay/Makefile.am | 3 ++-
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relay/dhcrelay.c | 29 +++++++++++++++++++++++++++++
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7 files changed, 131 insertions(+), 2 deletions(-)
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diff --git a/client/Makefile.am b/client/Makefile.am
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index d177159..0689185 100644
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--- a/client/Makefile.am
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+++ b/client/Makefile.am
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@@ -17,6 +17,7 @@ dhclient_LDADD = ../common/libdhcp.@A@ ../omapip/libomapi.@A@ \
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@BINDLIBIRSDIR@/libirs.@A@ \
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@BINDLIBDNSDIR@/libdns.@A@ \
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@BINDLIBISCCFGDIR@/libisccfg.@A@ \
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- @BINDLIBISCDIR@/libisc.@A@
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+ @BINDLIBISCDIR@/libisc.@A@ \
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+ $(CAPNG_LDADD)
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man_MANS = dhclient.8 dhclient-script.8 dhclient.conf.5 dhclient.leases.5
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EXTRA_DIST = $(man_MANS)
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diff --git a/client/dhclient-script.8 b/client/dhclient-script.8
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index 0db5516..2eddb8f 100644
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--- a/client/dhclient-script.8
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+++ b/client/dhclient-script.8
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@@ -243,6 +243,16 @@ repeatedly initialized to the values provided by one server, and then
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the other. Assuming the information provided by both servers is
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valid, this shouldn't cause any real problems, but it could be
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confusing.
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+.PP
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+Normally, if dhclient was compiled with libcap-ng support,
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+dhclient drops most capabilities immediately upon startup.
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+While more secure, this greatly restricts the additional actions that
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+hooks in dhclient-script can take. For example, any daemons that
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+dhclient-script starts or restarts will inherit the restricted
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+capabilities as well, which may interfere with their correct operation.
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+Thus, the
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+.BI \-nc
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+option can be used to prevent dhclient from dropping capabilities.
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.SH SEE ALSO
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dhclient(8), dhcpd(8), dhcrelay(8), dhclient.conf(5) and
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dhclient.leases(5).
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diff --git a/client/dhclient.8 b/client/dhclient.8
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index 6d7fbdb..0145b9f 100644
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--- a/client/dhclient.8
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+++ b/client/dhclient.8
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@@ -134,6 +134,9 @@ dhclient - Dynamic Host Configuration Protocol Client
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.B -w
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]
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[
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+.B -nc
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+]
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+[
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.B -B
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]
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[
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@@ -328,6 +331,32 @@ not to exit when it doesn't find any such interfaces. The
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program can then be used to notify the client when a network interface
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has been added or removed, so that the client can attempt to configure an IP
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address on that interface.
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+.TP
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+.BI \-nc
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+Do not drop capabilities.
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+
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+Normally, if
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+.B dhclient
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+was compiled with libcap-ng support,
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+.B dhclient
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+drops most capabilities immediately upon startup. While more secure,
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+this greatly restricts the additional actions that hooks in
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+.B dhclient-script (8)
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+can take. (For example, any daemons that
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+.B dhclient-script (8)
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+starts or restarts will inherit the restricted capabilities as well,
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+which may interfere with their correct operation.) Thus, the
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+.BI \-nc
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+option can be used to prevent
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+.B dhclient
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+from dropping capabilities.
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+
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+The
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+.BI \-nc
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+option is ignored if
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+.B dhclient
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+was not compiled with libcap-ng support.
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+
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.TP
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.BI \-n
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Do not configure any interfaces. This is most likely to be useful in
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diff --git a/client/dhclient.c b/client/dhclient.c
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index a86ab9e..5d3f5bc 100644
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--- a/client/dhclient.c
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+++ b/client/dhclient.c
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@@ -41,6 +41,10 @@
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#include <sys/wait.h>
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#include <limits.h>
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+#ifdef HAVE_LIBCAP_NG
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+#include <cap-ng.h>
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+#endif
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+
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/*
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* Defined in stdio.h when _GNU_SOURCE is set, but we don't want to define
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* that when building ISC code.
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@@ -266,6 +270,9 @@ main(int argc, char **argv) {
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int timeout_arg = 0;
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char *arg_conf = NULL;
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int arg_conf_len = 0;
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+#ifdef HAVE_LIBCAP_NG
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+ int keep_capabilities = 0;
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+#endif
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/* Initialize client globals. */
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memset(&default_duid, 0, sizeof(default_duid));
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@@ -665,6 +672,10 @@ main(int argc, char **argv) {
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dhclient_request_options = argv[i];
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+ } else if (!strcmp(argv[i], "-nc")) {
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+#ifdef HAVE_LIBCAP_NG
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+ keep_capabilities = 1;
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+#endif
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} else if (argv[i][0] == '-') {
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usage("Unknown command: %s", argv[i]);
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} else if (interfaces_requested < 0) {
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@@ -725,6 +736,19 @@ main(int argc, char **argv) {
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path_dhclient_script = s;
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}
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+#ifdef HAVE_LIBCAP_NG
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+ /* Drop capabilities */
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+ if (!keep_capabilities) {
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+ capng_clear(CAPNG_SELECT_CAPS);
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+ capng_update(CAPNG_ADD, CAPNG_EFFECTIVE|CAPNG_PERMITTED,
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+ CAP_DAC_OVERRIDE); // Drop this someday
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+ capng_updatev(CAPNG_ADD, CAPNG_EFFECTIVE|CAPNG_PERMITTED,
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+ CAP_NET_ADMIN, CAP_NET_RAW,
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+ CAP_NET_BIND_SERVICE, CAP_SYS_ADMIN, -1);
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+ capng_apply(CAPNG_SELECT_CAPS);
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+ }
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+#endif
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+
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/* Set up the initial dhcp option universe. */
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initialize_common_option_spaces();
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diff --git a/configure.ac b/configure.ac
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index a797438..15fc0d7 100644
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--- a/configure.ac
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+++ b/configure.ac
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@@ -612,6 +612,41 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[void foo() __attribute__((noreturn));
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# Look for optional headers.
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AC_CHECK_HEADERS(sys/socket.h net/if_dl.h net/if6.h regex.h)
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+# look for capabilities library
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+AC_ARG_WITH(libcap-ng,
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+ [ --with-libcap-ng=[auto/yes/no] Add Libcap-ng support [default=auto]],,
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+ with_libcap_ng=auto)
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+
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+# Check for Libcap-ng API
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+#
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+# libcap-ng detection
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+if test x$with_libcap_ng = xno ; then
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+ have_libcap_ng=no;
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+else
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+ # Start by checking for header file
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+ AC_CHECK_HEADER(cap-ng.h, capng_headers=yes, capng_headers=no)
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+
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+ # See if we have libcap-ng library
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+ AC_CHECK_LIB(cap-ng, capng_clear,
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+ CAPNG_LDADD=-lcap-ng,)
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+
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+ # Check results are usable
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+ if test x$with_libcap_ng = xyes -a x$CAPNG_LDADD = x ; then
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+ AC_MSG_ERROR(libcap-ng support was requested and the library was not found)
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+ fi
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+ if test x$CAPNG_LDADD != x -a $capng_headers = no ; then
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+ AC_MSG_ERROR(libcap-ng libraries found but headers are missing)
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+ fi
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+fi
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+AC_SUBST(CAPNG_LDADD)
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+AC_MSG_CHECKING(whether to use libcap-ng)
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+if test x$CAPNG_LDADD != x ; then
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+ AC_DEFINE(HAVE_LIBCAP_NG,1,[libcap-ng support])
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+ AC_MSG_RESULT(yes)
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+else
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+ AC_MSG_RESULT(no)
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+fi
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+
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# Solaris needs some libraries for functions
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AC_SEARCH_LIBS(socket, [socket])
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AC_SEARCH_LIBS(inet_ntoa, [nsl])
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diff --git a/relay/Makefile.am b/relay/Makefile.am
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index 2ba5979..8900e0b 100644
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--- a/relay/Makefile.am
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+++ b/relay/Makefile.am
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@@ -6,7 +6,8 @@ dhcrelay_LDADD = ../common/libdhcp.@A@ ../omapip/libomapi.@A@ \
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@BINDLIBIRSDIR@/libirs.@A@ \
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@BINDLIBDNSDIR@/libdns.@A@ \
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@BINDLIBISCCFGDIR@/libisccfg.@A@ \
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- @BINDLIBISCDIR@/libisc.@A@
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+ @BINDLIBISCDIR@/libisc.@A@ \
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+ $(CAPNG_LDADD)
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man_MANS = dhcrelay.8
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EXTRA_DIST = $(man_MANS)
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diff --git a/relay/dhcrelay.c b/relay/dhcrelay.c
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index ea1be18..7b4f4f1 100644
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--- a/relay/dhcrelay.c
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+++ b/relay/dhcrelay.c
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@@ -32,6 +32,11 @@
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#include <sys/time.h>
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#include <isc/file.h>
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+#ifdef HAVE_LIBCAP_NG
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+# include <cap-ng.h>
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+ int keep_capabilities = 0;
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+#endif
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+
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TIME default_lease_time = 43200; /* 12 hours... */
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TIME max_lease_time = 86400; /* 24 hours... */
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struct tree_cache *global_options[256];
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@@ -590,6 +595,10 @@ main(int argc, char **argv) {
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if (++i == argc)
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usage(use_noarg, argv[i-1]);
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dhcrelay_sub_id = argv[i];
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+#endif
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+ } else if (!strcmp(argv[i], "-nc")) {
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+#ifdef HAVE_LIBCAP_NG
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+ keep_capabilities = 1;
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#endif
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} else if (!strcmp(argv[i], "-pf")) {
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if (++i == argc)
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@@ -660,6 +669,17 @@ main(int argc, char **argv) {
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#endif
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}
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+#ifdef HAVE_LIBCAP_NG
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+ /* Drop capabilities */
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+ if (!keep_capabilities) {
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+ capng_clear(CAPNG_SELECT_BOTH);
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+ capng_updatev(CAPNG_ADD, CAPNG_EFFECTIVE|CAPNG_PERMITTED,
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+ CAP_NET_RAW, CAP_NET_BIND_SERVICE, -1);
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+ capng_apply(CAPNG_SELECT_BOTH);
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+ log_info ("Dropped all unnecessary capabilities.");
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+ }
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+#endif
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+
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if (!quiet) {
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log_info("%s %s", message, PACKAGE_VERSION);
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log_info(copyright);
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@@ -816,6 +836,15 @@ main(int argc, char **argv) {
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signal(SIGTERM, dhcp_signal_handler); /* kill */
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#endif
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+#ifdef HAVE_LIBCAP_NG
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+ /* Drop all capabilities */
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+ if (!keep_capabilities) {
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+ capng_clear(CAPNG_SELECT_BOTH);
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+ capng_apply(CAPNG_SELECT_BOTH);
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+ log_info ("Dropped all capabilities.");
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+ }
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+#endif
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+
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/* Start dispatching packets and timeouts... */
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dispatch();
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--
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2.14.5
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