Merge branch 'gre-reapply-ipv6-link-local-address-generation-fix'

Guillaume Nault says:

====================
gre: Reapply IPv6 link-local address generation fix.

Reintroduce the IPv6 link-local address generation fix for GRE and its
kernel selftest. These patches were introduced by merge commit
b3fc5927de4b ("Merge branch
'gre-fix-regressions-in-ipv6-link-local-address-generation'") but have
been reverted by commit 8417db0be5bb ("Merge branch
'gre-revert-ipv6-link-local-address-fix'"), because it uncovered
another bug in multipath routing. Now that this bug has been
investigated and fixed, we can apply the GRE link-local address fix
and its kernel selftest again.

For convenience, here's the original cover letter:

    IPv6 link-local address generation has some special cases for GRE
    devices. This has led to several regressions in the past, and some of
    them are still not fixed. This series fixes the remaining problems,
    like the ipv6.conf.<dev>.addr_gen_mode sysctl being ignored and the
    router discovery process not being started (see details in patch 1).

    To avoid any further regressions, patch 2 adds selftests covering
    IPv4 and IPv6 gre/gretap devices with all combinations of currently
    supported addr_gen_mode values.
====================

Link: https://patch.msgid.link/cover.1746225213.git.gnault@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 187 insertions, 6 deletions

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 9ba83f0c9928..c6b22170dc49 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3214,16 +3214,13 @@ static void add_v4_addrs(struct inet6_dev *idev)
 	struct in6_addr addr;
 	struct net_device *dev;
 	struct net *net = dev_net(idev->dev);
-	int scope, plen, offset = 0;
+	int scope, plen;
 	u32 pflags = 0;
 
 	ASSERT_RTNL();
 
 	memset(&addr, 0, sizeof(struct in6_addr));
-	/* in case of IP6GRE the dev_addr is an IPv6 and therefore we use only the last 4 bytes */
-	if (idev->dev->addr_len == sizeof(struct in6_addr))
-		offset = sizeof(struct in6_addr) - 4;
-	memcpy(&addr.s6_addr32[3], idev->dev->dev_addr + offset, 4);
+	memcpy(&addr.s6_addr32[3], idev->dev->dev_addr, 4);
 
 	if (!(idev->dev->flags & IFF_POINTOPOINT) && idev->dev->type == ARPHRD_SIT) {
 		scope = IPV6_ADDR_COMPATv4;
@@ -3534,7 +3531,13 @@ static void addrconf_gre_config(struct net_device *dev)
 		return;
 	}
 
-	if (dev->type == ARPHRD_ETHER) {
+	/* Generate the IPv6 link-local address using addrconf_addr_gen(),
+	 * unless we have an IPv4 GRE device not bound to an IP address and
+	 * which is in EUI64 mode (as __ipv6_isatap_ifid() would fail in this
+	 * case). Such devices fall back to add_v4_addrs() instead.
+	 */
+	if (!(dev->type == ARPHRD_IPGRE && *(__be32 *)dev->dev_addr == 0 &&
+	      idev->cnf.addr_gen_mode == IN6_ADDR_GEN_MODE_EUI64)) {
 		addrconf_addr_gen(idev, true);
 		return;
 	}
diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 124078b56fa4..70a38f485d4d 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -31,6 +31,7 @@ TEST_PROGS += veth.sh
 TEST_PROGS += ioam6.sh
 TEST_PROGS += gro.sh
 TEST_PROGS += gre_gso.sh
+TEST_PROGS += gre_ipv6_lladdr.sh
 TEST_PROGS += cmsg_so_mark.sh
 TEST_PROGS += cmsg_so_priority.sh
 TEST_PROGS += test_so_rcv.sh
diff --git a/tools/testing/selftests/net/gre_ipv6_lladdr.sh b/tools/testing/selftests/net/gre_ipv6_lladdr.sh
new file mode 100755
index 000000000000..5b34f6e1f831
--- /dev/null
+++ b/tools/testing/selftests/net/gre_ipv6_lladdr.sh
@@ -0,0 +1,177 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+source ./lib.sh
+
+PAUSE_ON_FAIL="no"
+
+# The trap function handler
+#
+exit_cleanup_all()
+{
+	cleanup_all_ns
+
+	exit "${EXIT_STATUS}"
+}
+
+# Add fake IPv4 and IPv6 networks on the loopback device, to be used as
+# underlay by future GRE devices.
+#
+setup_basenet()
+{
+	ip -netns "${NS0}" link set dev lo up
+	ip -netns "${NS0}" address add dev lo 192.0.2.10/24
+	ip -netns "${NS0}" address add dev lo 2001:db8::10/64 nodad
+}
+
+# Check if network device has an IPv6 link-local address assigned.
+#
+# Parameters:
+#
+#   * $1: The network device to test
+#   * $2: An extra regular expression that should be matched (to verify the
+#         presence of extra attributes)
+#   * $3: The expected return code from grep (to allow checking the absence of
+#         a link-local address)
+#   * $4: The user visible name for the scenario being tested
+#
+check_ipv6_ll_addr()
+{
+	local DEV="$1"
+	local EXTRA_MATCH="$2"
+	local XRET="$3"
+	local MSG="$4"
+
+	RET=0
+	set +e
+	ip -netns "${NS0}" -6 address show dev "${DEV}" scope link | grep "fe80::" | grep -q "${EXTRA_MATCH}"
+	check_err_fail "${XRET}" $? ""
+	log_test "${MSG}"
+	set -e
+}
+
+# Create a GRE device and verify that it gets an IPv6 link-local address as
+# expected.
+#
+# Parameters:
+#
+#   * $1: The device type (gre, ip6gre, gretap or ip6gretap)
+#   * $2: The local underlay IP address (can be an IPv4, an IPv6 or "any")
+#   * $3: The remote underlay IP address (can be an IPv4, an IPv6 or "any")
+#   * $4: The IPv6 interface identifier generation mode to use for the GRE
+#         device (eui64, none, stable-privacy or random).
+#
+test_gre_device()
+{
+	local GRE_TYPE="$1"
+	local LOCAL_IP="$2"
+	local REMOTE_IP="$3"
+	local MODE="$4"
+	local ADDR_GEN_MODE
+	local MATCH_REGEXP
+	local MSG
+
+	ip link add netns "${NS0}" name gretest type "${GRE_TYPE}" local "${LOCAL_IP}" remote "${REMOTE_IP}"
+
+	case "${MODE}" in
+	    "eui64")
+		ADDR_GEN_MODE=0
+		MATCH_REGEXP=""
+		MSG="${GRE_TYPE}, mode: 0 (EUI64), ${LOCAL_IP} -> ${REMOTE_IP}"
+		XRET=0
+		;;
+	    "none")
+		ADDR_GEN_MODE=1
+		MATCH_REGEXP=""
+		MSG="${GRE_TYPE}, mode: 1 (none), ${LOCAL_IP} -> ${REMOTE_IP}"
+		XRET=1 # No link-local address should be generated
+		;;
+	    "stable-privacy")
+		ADDR_GEN_MODE=2
+		MATCH_REGEXP="stable-privacy"
+		MSG="${GRE_TYPE}, mode: 2 (stable privacy), ${LOCAL_IP} -> ${REMOTE_IP}"
+		XRET=0
+		# Initialise stable_secret (required for stable-privacy mode)
+		ip netns exec "${NS0}" sysctl -qw net.ipv6.conf.gretest.stable_secret="2001:db8::abcd"
+		;;
+	    "random")
+		ADDR_GEN_MODE=3
+		MATCH_REGEXP="stable-privacy"
+		MSG="${GRE_TYPE}, mode: 3 (random), ${LOCAL_IP} -> ${REMOTE_IP}"
+		XRET=0
+		;;
+	esac
+
+	# Check that IPv6 link-local address is generated when device goes up
+	ip netns exec "${NS0}" sysctl -qw net.ipv6.conf.gretest.addr_gen_mode="${ADDR_GEN_MODE}"
+	ip -netns "${NS0}" link set dev gretest up
+	check_ipv6_ll_addr gretest "${MATCH_REGEXP}" "${XRET}" "config: ${MSG}"
+
+	# Now disable link-local address generation
+	ip -netns "${NS0}" link set dev gretest down
+	ip netns exec "${NS0}" sysctl -qw net.ipv6.conf.gretest.addr_gen_mode=1
+	ip -netns "${NS0}" link set dev gretest up
+
+	# Check that link-local address generation works when re-enabled while
+	# the device is already up
+	ip netns exec "${NS0}" sysctl -qw net.ipv6.conf.gretest.addr_gen_mode="${ADDR_GEN_MODE}"
+	check_ipv6_ll_addr gretest "${MATCH_REGEXP}" "${XRET}" "update: ${MSG}"
+
+	ip -netns "${NS0}" link del dev gretest
+}
+
+test_gre4()
+{
+	local GRE_TYPE
+	local MODE
+
+	for GRE_TYPE in "gre" "gretap"; do
+		printf "\n####\nTesting IPv6 link-local address generation on ${GRE_TYPE} devices\n####\n\n"
+
+		for MODE in "eui64" "none" "stable-privacy" "random"; do
+			test_gre_device "${GRE_TYPE}" 192.0.2.10 192.0.2.11 "${MODE}"
+			test_gre_device "${GRE_TYPE}" any 192.0.2.11 "${MODE}"
+			test_gre_device "${GRE_TYPE}" 192.0.2.10 any "${MODE}"
+		done
+	done
+}
+
+test_gre6()
+{
+	local GRE_TYPE
+	local MODE
+
+	for GRE_TYPE in "ip6gre" "ip6gretap"; do
+		printf "\n####\nTesting IPv6 link-local address generation on ${GRE_TYPE} devices\n####\n\n"
+
+		for MODE in "eui64" "none" "stable-privacy" "random"; do
+			test_gre_device "${GRE_TYPE}" 2001:db8::10 2001:db8::11 "${MODE}"
+			test_gre_device "${GRE_TYPE}" any 2001:db8::11 "${MODE}"
+			test_gre_device "${GRE_TYPE}" 2001:db8::10 any "${MODE}"
+		done
+	done
+}
+
+usage()
+{
+	echo "Usage: $0 [-p]"
+	exit 1
+}
+
+while getopts :p o
+do
+	case $o in
+		p) PAUSE_ON_FAIL="yes";;
+		*) usage;;
+	esac
+done
+
+setup_ns NS0
+
+set -e
+trap exit_cleanup_all EXIT
+
+setup_basenet
+
+test_gre4
+test_gre6