[PATCH net 0/2] gre: Revert IPv6 link-local address fix.

[PATCH net 0/2] gre: Revert IPv6 link-local address fix.

[Guillaume Nault]

Following Paolo's suggestion, let's revert the IPv6 link-local address
generation fix for GRE devices. The patch introduced regressions in the
upstream CI, which are still under investigation.

Start by reverting the kselftest that depend on that fix (patch 1), then
revert the kernel code itself (patch 2).

Guillaume Nault (2):
  Revert "selftests: Add IPv6 link-local address generation tests for
    GRE devices."
  Revert "gre: Fix IPv6 link-local address generation."

 net/ipv6/addrconf.c                           |  15 +-
 tools/testing/selftests/net/Makefile          |   1 -
 .../testing/selftests/net/gre_ipv6_lladdr.sh  | 177 ------------------
 3 files changed, 6 insertions(+), 187 deletions(-)
 delete mode 100755 tools/testing/selftests/net/gre_ipv6_lladdr.sh

-- 
2.39.2

[PATCH net 1/2] Revert "selftests: Add IPv6 link-local address generation tests for GRE devices."

[Guillaume Nault]

This reverts commit 6f50175ccad4278ed3a9394c00b797b75441bd6e.

Commit 183185a18ff9 ("gre: Fix IPv6 link-local address generation.") is
going to be reverted. So let's revert the corresponding kselftest
first.

Signed-off-by: Guillaume Nault <gnault@redhat.com>
---
 tools/testing/selftests/net/Makefile          |   1 -
 .../testing/selftests/net/gre_ipv6_lladdr.sh  | 177 ------------------
 2 files changed, 178 deletions(-)
 delete mode 100755 tools/testing/selftests/net/gre_ipv6_lladdr.sh

diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 5916f3b81c39..73ee88d6b043 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -31,7 +31,6 @@ 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 += cmsg_time.sh cmsg_ipv6.sh
diff --git a/tools/testing/selftests/net/gre_ipv6_lladdr.sh b/tools/testing/selftests/net/gre_ipv6_lladdr.sh
deleted file mode 100755
index 5b34f6e1f831..000000000000
--- a/tools/testing/selftests/net/gre_ipv6_lladdr.sh
+++ /dev/null
@@ -1,177 +0,0 @@
-#!/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
-- 
2.39.2

[PATCH net 2/2] Revert "gre: Fix IPv6 link-local address generation."

[Guillaume Nault]

This reverts commit 183185a18ff96751db52a46ccf93fff3a1f42815.

This patch broke net/forwarding/ip6gre_custom_multipath_hash.sh in some
circumstances (https://lore.kernel.org/netdev/Z9RIyKZDNoka53EO@mini-arch/).
Let's revert it while the problem is being investigated.

Fixes: 183185a18ff9 ("gre: Fix IPv6 link-local address generation.")
Signed-off-by: Guillaume Nault <gnault@redhat.com>
---
 net/ipv6/addrconf.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 8b6258819dad..ac8cc1076536 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3209,13 +3209,16 @@ 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;
+	int scope, plen, offset = 0;
 	u32 pflags = 0;
 
 	ASSERT_RTNL();
 
 	memset(&addr, 0, sizeof(struct in6_addr));
-	memcpy(&addr.s6_addr32[3], idev->dev->dev_addr, 4);
+	/* 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);
 
 	if (!(idev->dev->flags & IFF_POINTOPOINT) && idev->dev->type == ARPHRD_SIT) {
 		scope = IPV6_ADDR_COMPATv4;
@@ -3526,13 +3529,7 @@ static void addrconf_gre_config(struct net_device *dev)
 		return;
 	}
 
-	/* 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)) {
+	if (dev->type == ARPHRD_ETHER) {
 		addrconf_addr_gen(idev, true);
 		return;
 	}
-- 
2.39.2

Re: [PATCH net 0/2] gre: Revert IPv6 link-local address fix.

[Stanislav Fomichev]

On 03/19, Guillaume Nault wrote:
> Following Paolo's suggestion, let's revert the IPv6 link-local address
> generation fix for GRE devices. The patch introduced regressions in the
> upstream CI, which are still under investigation.
> 
> Start by reverting the kselftest that depend on that fix (patch 1), then
> revert the kernel code itself (patch 2).

Acked-by: Stanislav Fomichev <sdf@fomichev.me>

Re: [PATCH net 0/2] gre: Revert IPv6 link-local address fix.

[Paolo Abeni]

On 3/19/25 10:26 PM, Guillaume Nault wrote:
> Following Paolo's suggestion, let's revert the IPv6 link-local address
> generation fix for GRE devices. The patch introduced regressions in the
> upstream CI, which are still under investigation.
> 
> Start by reverting the kselftest that depend on that fix (patch 1), then
> revert the kernel code itself (patch 2).
> 
> Guillaume Nault (2):
>   Revert "selftests: Add IPv6 link-local address generation tests for
>     GRE devices."
>   Revert "gre: Fix IPv6 link-local address generation."
> 
>  net/ipv6/addrconf.c                           |  15 +-
>  tools/testing/selftests/net/Makefile          |   1 -
>  .../testing/selftests/net/gre_ipv6_lladdr.sh  | 177 ------------------
>  3 files changed, 6 insertions(+), 187 deletions(-)
>  delete mode 100755 tools/testing/selftests/net/gre_ipv6_lladdr.sh

I'm going to apply this series well below the 24 grace period, to fit
tomorrow's PR.

Any feedback more than welcome, but it need to be fast ;)

Thanks,

Paolo

Re: [PATCH net 0/2] gre: Revert IPv6 link-local address fix.

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Wed, 19 Mar 2025 22:26:39 +0100 you wrote:
> Following Paolo's suggestion, let's revert the IPv6 link-local address
> generation fix for GRE devices. The patch introduced regressions in the
> upstream CI, which are still under investigation.
> 
> Start by reverting the kselftest that depend on that fix (patch 1), then
> revert the kernel code itself (patch 2).
> 
> [...]

Here is the summary with links:
  - [net,1/2] Revert "selftests: Add IPv6 link-local address generation tests for GRE devices."
    https://git.kernel.org/netdev/net/c/355d940f4d5a
  - [net,2/2] Revert "gre: Fix IPv6 link-local address generation."
    https://git.kernel.org/netdev/net/c/fc486c2d060f

You are awesome, thank you!
-- 
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