It is currently impossible to enable ipv6 forwarding on a per-interface
basis like in ipv4. To enable forwarding on an ipv6 interface we need to
enable it on all interfaces and disable it on the other interfaces using
a netfilter rule. This is especially cumbersome if you have lots of
interface and only want to enable forwarding on a few. According to the
sysctl docs [0] the `net.ipv6.conf.all.forwarding` enables forwarding
for all interfaces, while the interface-specific
`net.ipv6.conf.<interface>.forwarding` configures the interface
Host/Router configuration.
Introduce a new sysctl flag `force_forwarding`, which can be set on every
interface. The ip6_forwarding function will then check if the global
forwarding flag OR the force_forwarding flag is active and forward the
packet.
To preserver backwards-compatibility reset the flag (on all interfaces)
to 0 if the net.ipv6.conf.all.forwarding flag is set to 0.
Add a short selftest that checks if a packet gets forwarded with and
without `force_forwarding`.
[0]: https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt
Signed-off-by: Gabriel Goller <g.goller(a)proxmox.com>
---
First time writing a selftest, so LMK if I did something wrong or if
there is something I can improve. Thanks!
v4:
* actually write the sysctl value to the table
* use ASSERT_RTNL() when forwarding the sysctl change
* remove useless comments in function body
* simplify forwarding and force_forwarding check in ip6_output.c
* fix code backticks in Documentation (double instead of single)
* add selftests
v3: https://lore.kernel.org/netdev/20250702074619.139031-1-g.goller@proxmox.com/
* remove forwarding=0 setting force_forwarding=0 globally.
* add min and max (0 and 1) value to sysctl.
v2: https://lore.kernel.org/netdev/20250701140423.487411-1-g.goller@proxmox.com/
* rename from `do_forwarding` to `force_forwarding`.
* add global `force_forwarding` flag which will enable
`force_forwarding` on every interface like the
`ipv4.all.forwarding` flag.
* `forwarding`=0 will disable global and per-interface
`force_forwarding`.
* export option as NETCONFA_FORCE_FORWARDING.
v1: https://lore.kernel.org/netdev/20250702074619.139031-1-g.goller@proxmox.com/
Documentation/networking/ip-sysctl.rst | 5 +
include/linux/ipv6.h | 1 +
include/uapi/linux/ipv6.h | 1 +
include/uapi/linux/netconf.h | 1 +
include/uapi/linux/sysctl.h | 1 +
net/ipv6/addrconf.c | 91 +++++++++++++++
net/ipv6/ip6_output.c | 3 +-
tools/testing/selftests/net/Makefile | 1 +
.../selftests/net/ipv6_force_forwarding.sh | 105 ++++++++++++++++++
9 files changed, 208 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/net/ipv6_force_forwarding.sh
diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 0f1251cce314..ec7fa1e890f1 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -2292,6 +2292,11 @@ conf/all/forwarding - BOOLEAN
proxy_ndp - BOOLEAN
Do proxy ndp.
+force_forwarding - BOOLEAN
+ Enable forwarding on this interface only -- regardless of the setting on
+ ``conf/all/forwarding``. When setting ``conf.all.forwarding`` to 0,
+ the ``force_forwarding`` flag will be reset on all interfaces.
+
fwmark_reflect - BOOLEAN
Controls the fwmark of kernel-generated IPv6 reply packets that are not
associated with a socket for example, TCP RSTs or ICMPv6 echo replies).
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 5aeeed22f35b..5380107e466c 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -19,6 +19,7 @@ struct ipv6_devconf {
__s32 forwarding;
__s32 disable_policy;
__s32 proxy_ndp;
+ __s32 force_forwarding;
__cacheline_group_end(ipv6_devconf_read_txrx);
__s32 accept_ra;
diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
index cf592d7b630f..d4d3ae774b26 100644
--- a/include/uapi/linux/ipv6.h
+++ b/include/uapi/linux/ipv6.h
@@ -199,6 +199,7 @@ enum {
DEVCONF_NDISC_EVICT_NOCARRIER,
DEVCONF_ACCEPT_UNTRACKED_NA,
DEVCONF_ACCEPT_RA_MIN_LFT,
+ DEVCONF_FORCE_FORWARDING,
DEVCONF_MAX
};
diff --git a/include/uapi/linux/netconf.h b/include/uapi/linux/netconf.h
index fac4edd55379..1c8c84d65ae3 100644
--- a/include/uapi/linux/netconf.h
+++ b/include/uapi/linux/netconf.h
@@ -19,6 +19,7 @@ enum {
NETCONFA_IGNORE_ROUTES_WITH_LINKDOWN,
NETCONFA_INPUT,
NETCONFA_BC_FORWARDING,
+ NETCONFA_FORCE_FORWARDING,
__NETCONFA_MAX
};
#define NETCONFA_MAX (__NETCONFA_MAX - 1)
diff --git a/include/uapi/linux/sysctl.h b/include/uapi/linux/sysctl.h
index 8981f00204db..63d1464cb71c 100644
--- a/include/uapi/linux/sysctl.h
+++ b/include/uapi/linux/sysctl.h
@@ -573,6 +573,7 @@ enum {
NET_IPV6_ACCEPT_RA_FROM_LOCAL=26,
NET_IPV6_ACCEPT_RA_RT_INFO_MIN_PLEN=27,
NET_IPV6_RA_DEFRTR_METRIC=28,
+ NET_IPV6_FORCE_FORWARDING=29,
__NET_IPV6_MAX
};
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index ba2ec7c870cc..dcf4e8bf8cf8 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -239,6 +239,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
.ndisc_evict_nocarrier = 1,
.ra_honor_pio_life = 0,
.ra_honor_pio_pflag = 0,
+ .force_forwarding = 0,
};
static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
@@ -303,6 +304,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
.ndisc_evict_nocarrier = 1,
.ra_honor_pio_life = 0,
.ra_honor_pio_pflag = 0,
+ .force_forwarding = 0,
};
/* Check if link is ready: is it up and is a valid qdisc available */
@@ -857,6 +859,15 @@ static void addrconf_forward_change(struct net *net, __s32 newf)
idev = __in6_dev_get_rtnl_net(dev);
if (idev) {
int changed = (!idev->cnf.forwarding) ^ (!newf);
+ /*
+ * With the introduction of force_forwarding, we need to be backwards
+ * compatible, so that means we need to set the force_forwarding flag
+ * on every interface to 0 if net.ipv6.conf.all.forwarding is set to 0.
+ * This allows the global forwarding flag to disable forwarding for
+ * all interfaces.
+ */
+ if (newf == 0)
+ WRITE_ONCE(idev->cnf.force_forwarding, newf);
WRITE_ONCE(idev->cnf.forwarding, newf);
if (changed)
@@ -5719,6 +5730,7 @@ static void ipv6_store_devconf(const struct ipv6_devconf *cnf,
array[DEVCONF_ACCEPT_UNTRACKED_NA] =
READ_ONCE(cnf->accept_untracked_na);
array[DEVCONF_ACCEPT_RA_MIN_LFT] = READ_ONCE(cnf->accept_ra_min_lft);
+ array[DEVCONF_FORCE_FORWARDING] = READ_ONCE(cnf->force_forwarding);
}
static inline size_t inet6_ifla6_size(void)
@@ -6747,6 +6759,78 @@ static int addrconf_sysctl_disable_policy(const struct ctl_table *ctl, int write
return ret;
}
+static void addrconf_force_forward_change(struct net *net, __s32 newf)
+{
+ ASSERT_RTNL();
+ struct net_device *dev;
+ struct inet6_dev *idev;
+
+ for_each_netdev(net, dev) {
+ idev = __in6_dev_get_rtnl_net(dev);
+ if (idev) {
+ int changed = (!idev->cnf.force_forwarding) ^ (!newf);
+
+ WRITE_ONCE(idev->cnf.force_forwarding, newf);
+ if (changed) {
+ inet6_netconf_notify_devconf(dev_net(dev), RTM_NEWNETCONF,
+ NETCONFA_FORCE_FORWARDING,
+ dev->ifindex, &idev->cnf);
+ }
+ }
+ }
+}
+
+static int addrconf_sysctl_force_forwarding(const struct ctl_table *ctl, int write,
+ void *buffer, size_t *lenp, loff_t *ppos)
+{
+ struct inet6_dev *idev = ctl->extra1;
+ struct net *net = ctl->extra2;
+ int *valp = ctl->data;
+ loff_t pos = *ppos;
+ int new_val = *valp;
+ int old_val = *valp;
+ int ret;
+
+ struct ctl_table tmp_ctl = *ctl;
+
+ tmp_ctl.extra1 = SYSCTL_ZERO;
+ tmp_ctl.extra2 = SYSCTL_ONE;
+ tmp_ctl.data = &new_val;
+
+ ret = proc_douintvec_minmax(&tmp_ctl, write, buffer, lenp, ppos);
+
+ if (write && old_val != new_val) {
+ if (!rtnl_net_trylock(net))
+ return restart_syscall();
+
+ if (valp == &net->ipv6.devconf_dflt->force_forwarding) {
+ inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
+ NETCONFA_FORCE_FORWARDING,
+ NETCONFA_IFINDEX_DEFAULT,
+ net->ipv6.devconf_dflt);
+ } else if (valp == &net->ipv6.devconf_all->force_forwarding) {
+ inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
+ NETCONFA_FORCE_FORWARDING,
+ NETCONFA_IFINDEX_ALL,
+ net->ipv6.devconf_all);
+
+ addrconf_force_forward_change(net, new_val);
+ } else {
+ inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
+ NETCONFA_FORCE_FORWARDING,
+ idev->dev->ifindex,
+ &idev->cnf);
+ }
+ rtnl_net_unlock(net);
+ }
+
+ if (write)
+ WRITE_ONCE(*valp, new_val);
+ if (ret)
+ *ppos = pos;
+ return ret;
+}
+
static int minus_one = -1;
static const int two_five_five = 255;
static u32 ioam6_if_id_max = U16_MAX;
@@ -7217,6 +7301,13 @@ static const struct ctl_table addrconf_sysctl[] = {
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_TWO,
},
+ {
+ .procname = "force_forwarding",
+ .data = &ipv6_devconf.force_forwarding,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = addrconf_sysctl_force_forwarding,
+ },
};
static int __addrconf_sysctl_register(struct net *net, char *dev_name,
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 7bd29a9ff0db..440b9efced72 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -509,7 +509,8 @@ int ip6_forward(struct sk_buff *skb)
u32 mtu;
idev = __in6_dev_get_safely(dev_get_by_index_rcu(net, IP6CB(skb)->iif));
- if (READ_ONCE(net->ipv6.devconf_all->forwarding) == 0)
+ if (idev && !READ_ONCE(idev->cnf.force_forwarding) &&
+ !READ_ONCE(net->ipv6.devconf_all->forwarding))
goto error;
if (skb->pkt_type != PACKET_HOST)
diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 332f387615d7..f64ec8a15a77 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -112,6 +112,7 @@ TEST_PROGS += skf_net_off.sh
TEST_GEN_FILES += skf_net_off
TEST_GEN_FILES += tfo
TEST_PROGS += tfo_passive.sh
+TEST_PROGS += ipv6_force_forwarding.sh
# YNL files, must be before "include ..lib.mk"
YNL_GEN_FILES := busy_poller netlink-dumps
diff --git a/tools/testing/selftests/net/ipv6_force_forwarding.sh b/tools/testing/selftests/net/ipv6_force_forwarding.sh
new file mode 100644
index 000000000000..62adc9d4afc9
--- /dev/null
+++ b/tools/testing/selftests/net/ipv6_force_forwarding.sh
@@ -0,0 +1,105 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Test IPv6 force_forwarding interface property
+#
+# This test verifies that the force_forwarding property works correctly:
+# - When global forwarding is disabled, packets are not forwarded normally
+# - When force_forwarding is enabled on an interface, packets are forwarded
+# regardless of the global forwarding setting
+
+source lib.sh
+
+cleanup() {
+ cleanup_ns $ns1 $ns2 $ns3
+}
+
+trap cleanup EXIT
+
+setup_test() {
+ # Create three namespaces: sender, router, receiver
+ setup_ns ns1 ns2 ns3
+
+ # Create veth pairs: ns1 <-> ns2 <-> ns3
+ ip link add name veth12 type veth peer name veth21
+ ip link add name veth23 type veth peer name veth32
+
+ # Move interfaces to namespaces
+ ip link set veth12 netns $ns1
+ ip link set veth21 netns $ns2
+ ip link set veth23 netns $ns2
+ ip link set veth32 netns $ns3
+
+ # Configure interfaces
+ ip -n $ns1 addr add 2001:db8:1::1/64 dev veth12
+ ip -n $ns2 addr add 2001:db8:1::2/64 dev veth21
+ ip -n $ns2 addr add 2001:db8:2::1/64 dev veth23
+ ip -n $ns3 addr add 2001:db8:2::2/64 dev veth32
+
+ # Bring up interfaces
+ ip -n $ns1 link set veth12 up
+ ip -n $ns2 link set veth21 up
+ ip -n $ns2 link set veth23 up
+ ip -n $ns3 link set veth32 up
+
+ # Add routes
+ ip -n $ns1 route add 2001:db8:2::/64 via 2001:db8:1::2
+ ip -n $ns3 route add 2001:db8:1::/64 via 2001:db8:2::1
+
+ # Disable global forwarding
+ ip netns exec $ns2 sysctl -qw net.ipv6.conf.all.forwarding=0
+}
+
+test_force_forwarding() {
+ local ret=0
+
+ echo "TEST: force_forwarding functionality"
+
+ # Check if force_forwarding sysctl exists
+ if ! ip netns exec $ns2 test -f /proc/sys/net/ipv6/conf/veth21/force_forwarding; then
+ echo "SKIP: force_forwarding not available"
+ return $ksft_skip
+ fi
+
+ # Test 1: Without force_forwarding, ping should fail
+ ip netns exec $ns2 sysctl -qw net.ipv6.conf.veth21.force_forwarding=0
+ ip netns exec $ns2 sysctl -qw net.ipv6.conf.veth23.force_forwarding=0
+
+ if ip netns exec $ns1 ping -6 -c 1 -W 2 2001:db8:2::2 &>/dev/null; then
+ echo "FAIL: ping succeeded when forwarding disabled"
+ ret=1
+ else
+ echo "PASS: forwarding disabled correctly"
+ fi
+
+ # Test 2: With force_forwarding enabled, ping should succeed
+ ip netns exec $ns2 sysctl -qw net.ipv6.conf.veth21.force_forwarding=1
+ ip netns exec $ns2 sysctl -qw net.ipv6.conf.veth23.force_forwarding=1
+
+ if ip netns exec $ns1 ping -6 -c 1 -W 2 2001:db8:2::2 &>/dev/null; then
+ echo "PASS: force_forwarding enabled forwarding"
+ else
+ echo "FAIL: ping failed with force_forwarding enabled"
+ ret=1
+ fi
+
+ return $ret
+}
+
+echo "IPv6 force_forwarding test"
+echo "=========================="
+
+setup_test
+test_force_forwarding
+ret=$?
+
+if [ $ret -eq 0 ]; then
+ echo "OK"
+ exit 0
+elif [ $ret -eq $ksft_skip ]; then
+ echo "SKIP"
+ exit $ksft_skip
+else
+ echo "FAIL"
+ exit 1
+fi
--
2.39.5
I had cause to look at the vfork() support for GCS and realised that we
don't have any direct test coverage, this series does so by adding
vfork() to nolibc and then using that in basic-gcs to provide some
simple vfork() coverage.
Signed-off-by: Mark Brown <broonie(a)kernel.org>
---
Changes in v3:
- Stylistic nits in the GCS vfork() test.
- SPARC has a non-standard vfork() ABI which needs handling.
- Link to v2: https://lore.kernel.org/r/20250610-arm64-gcs-vfork-exit-v2-0-929443dfcf82@k…
Changes in v2:
- Add replacement of ifdef with if defined() in nolibc since the code
doesn't reflect the coding style.
- Remove check for arch specific vfork().
- Link to v1: https://lore.kernel.org/r/20250609-arm64-gcs-vfork-exit-v1-0-baad0f085747@k…
---
Mark Brown (4):
tools/nolibc: Replace ifdef with if defined() in sys.h
tools/nolibc: Provide vfork()
kselftest/arm64: Add a test for vfork() with GCS
selftests/nolibc: Add coverage of vfork()
tools/include/nolibc/arch-sparc.h | 16 +++++++
tools/include/nolibc/sys.h | 59 ++++++++++++++++++-------
tools/testing/selftests/arm64/gcs/basic-gcs.c | 63 +++++++++++++++++++++++++++
tools/testing/selftests/nolibc/nolibc-test.c | 23 ++++++++--
4 files changed, 142 insertions(+), 19 deletions(-)
---
base-commit: 86731a2a651e58953fc949573895f2fa6d456841
change-id: 20250528-arm64-gcs-vfork-exit-4a7daf7652ee
Best regards,
--
Mark Brown <broonie(a)kernel.org>
The kunit test that checks the longests symbol length [1], has triggered
warnings in some pilelines when symbol prefixes are used [2][3]. The test
will to depend on !PREFIX_SYMBOLS and !CFI_CLANG as sujested in [4] and
on !GCOV_KERNEL.
[1] https://lore.kernel.org/rust-for-linux/CABVgOSm=5Q0fM6neBhxSbOUHBgNzmwf2V22…
[2] https://lore.kernel.org/all/20250328112156.2614513-1-arnd@kernel.org/T/#u
[3] https://lore.kernel.org/rust-for-linux/bbd03b37-c4d9-4a92-9be2-75aaf8c19815…
[4] https://lore.kernel.org/linux-kselftest/20250427200916.GA1661412@ax162/T/#t
Reviewed-by: Rae Moar <rmoar(a)google.com>
Signed-off-by: Sergio González Collado <sergio.collado(a)gmail.com>
---
v2 -> v3: added dependency on !GCOV_KERNEL (to avoid __gcov_ prefix)
---
v1 -> v2: added dependency on !CFI_CLANG as suggested in [3], removed
CONFIG_ prefix
---
lib/Kconfig.debug | 1 +
lib/tests/longest_symbol_kunit.c | 3 +--
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index f9051ab610d5..e55c761eae20 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2886,6 +2886,7 @@ config FORTIFY_KUNIT_TEST
config LONGEST_SYM_KUNIT_TEST
tristate "Test the longest symbol possible" if !KUNIT_ALL_TESTS
depends on KUNIT && KPROBES
+ depends on !PREFIX_SYMBOLS && !CFI_CLANG && !GCOV_KERNEL
default KUNIT_ALL_TESTS
help
Tests the longest symbol possible
diff --git a/lib/tests/longest_symbol_kunit.c b/lib/tests/longest_symbol_kunit.c
index e3c28ff1807f..9b4de3050ba7 100644
--- a/lib/tests/longest_symbol_kunit.c
+++ b/lib/tests/longest_symbol_kunit.c
@@ -3,8 +3,7 @@
* Test the longest symbol length. Execute with:
* ./tools/testing/kunit/kunit.py run longest-symbol
* --arch=x86_64 --kconfig_add CONFIG_KPROBES=y --kconfig_add CONFIG_MODULES=y
- * --kconfig_add CONFIG_RETPOLINE=n --kconfig_add CONFIG_CFI_CLANG=n
- * --kconfig_add CONFIG_MITIGATION_RETPOLINE=n
+ * --kconfig_add CONFIG_CPU_MITIGATIONS=n --kconfig_add CONFIG_GCOV_KERNEL=n
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
base-commit: 1a80a098c606b285fb0a13aa992af4f86da1ff06
--
2.39.2