[PATCH net v2] macsec: check the resolved SCI for duplicates
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From: Haseeb Malik via B4 Relay <devnull+haseebulhaq55.gmail.com@kernel.org>
Date: 2026-10-01 20:40:18
Also in:
b4-sent, linux-kselftest, lkml
Subsystem:
kernel selftest framework, networking drivers, networking [macsec], the rest · Maintainers:
Shuah Khan, Shuah Khan, Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Sabrina Dubroca, Linus Torvalds
From: Haseeb Malik <redacted>
An all-ones IFLA_MACSEC_SCI selects the default SCI derived from the
MACsec device's MAC address and port 1. macsec_init_secy() resolves this
value and stores the result in secy.sci, but macsec_newlink() checks for
duplicates using the unchanged local sci argument.
Consequently, an all-ones request can create a second MACsec device with
the same transmit SCI on the same lower device, while requesting that
SCI explicitly returns -EBUSY.
Resolve an undefined SCI in macsec_newlink() before initializing the
SecY, so initialization and duplicate detection use the same value.
Preserve the all-ones fallback when the resulting SCI is available.
Add regression tests for duplicate rejection using default, explicit and
all-ones SCI requests, and for valid fallback and reuse after deletion.
Skip these local tests when iproute2 lacks MACsec support.
Fixes: c09440f7dcb3 ("macsec: introduce IEEE 802.1AE driver")
Link: https://lists.openwall.net/netdev/2026/09/16/11
Assisted-by: LLM
Signed-off-by: Haseeb Malik <redacted>
---
Changes in v2:
- Resolve undefined SCI in macsec_newlink(), as suggested by Sabrina.
- Check local iproute2 MACsec support in the new tests, as Sashiko noted.
Link to v1: https://lore.kernel.org/netdev/20260927-fix-macsec-duplicate-sci-v1-1-085bd742c8e9@gmail.com/ (local)
Tested on arm64/virtme with KASAN and lockdep: the new regression
tests go from 5 pass/2 fail to 7 pass/0 fail. The full MACsec selftest
passes all 15 cases without skips.
---
drivers/net/macsec.c | 8 ++--
tools/testing/selftests/drivers/net/macsec.py | 57 +++++++++++++++++++++++++--
2 files changed, 57 insertions(+), 8 deletions(-)
diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index 78a19b134632..69686f22eda8 100644
--- a/drivers/net/macsec.c
+++ b/drivers/net/macsec.c@@ -4143,9 +4143,6 @@ static void macsec_init_secy(struct net_device *dev, sci_t sci, u8 icv_len) struct macsec_dev *macsec = macsec_priv(dev); struct macsec_secy *secy = &macsec->secy; - if (sci == MACSEC_UNDEF_SCI) - sci = dev_to_sci(dev, MACSEC_PORT_ES); - secy->netdev = dev; secy->operational = true; secy->key_len = DEFAULT_SAK_LEN;
@@ -4178,7 +4175,7 @@ static int macsec_newlink(struct net_device *dev, u8 icv_len = MACSEC_DEFAULT_ICV_LEN; struct net_device *real_dev; int err, mtu; - sci_t sci; + sci_t sci = MACSEC_UNDEF_SCI; if (!tb[IFLA_LINK]) return -EINVAL;
@@ -4231,7 +4228,8 @@ static int macsec_newlink(struct net_device *dev, sci = nla_get_sci(data[IFLA_MACSEC_SCI]); else if (data && data[IFLA_MACSEC_PORT]) sci = dev_to_sci(dev, nla_get_be16(data[IFLA_MACSEC_PORT])); - else + + if (sci == MACSEC_UNDEF_SCI) sci = dev_to_sci(dev, MACSEC_PORT_ES); /* Registration can notify listeners before returning. */
diff --git a/tools/testing/selftests/drivers/net/macsec.py b/tools/testing/selftests/drivers/net/macsec.py
index 9a83d9542e04..81003bda9b0d 100755
--- a/tools/testing/selftests/drivers/net/macsec.py
+++ b/tools/testing/selftests/drivers/net/macsec.py@@ -34,9 +34,10 @@ def _get_features(dev): return ethtool(f"-k {dev}", json=True)[0] -def _require_ip_macsec(cfg): - """SKIP if iproute2 on local or remote lacks 'ip macsec' support.""" - for host in [None, cfg.remote]: +def _require_ip_macsec(cfg=None): + """SKIP if iproute2 lacks MACsec locally or on cfg.remote, when given.""" + hosts = [None, cfg.remote] if cfg is not None else [None] + for host in hosts: out = cmd("ip macsec help", fail=False, host=host) if "Usage" not in out.stdout + out.stderr: where = "remote" if host else "local"
@@ -263,6 +264,54 @@ def test_offload_state(cfg) -> None: "features should match first offload-on snapshot") +@ksft_variants([ + KsftNamedVariant("default", "", ""), + KsftNamedVariant("explicit", "", "sci {sci}"), + KsftNamedVariant("undefined", "", "sci ffffffffffffffff"), + KsftNamedVariant("undefined_default", "sci ffffffffffffffff", ""), + KsftNamedVariant("undefined_explicit", "sci ffffffffffffffff", "sci {sci}"), + KsftNamedVariant("undefined_twice", "sci ffffffffffffffff", + "sci ffffffffffffffff"), +]) +def test_duplicate_sci(cfg, first, second) -> None: + """Reject duplicate transmit SCIs, including the undefined-SCI fallback.""" + + _require_ip_macsec() + ms0 = _macsec_name(0) + ms1 = _macsec_name(1) + sci = _get_mac(cfg.ifname).replace(":", "") + "0001" + + ip(f"link add link {cfg.ifname} {ms0} type macsec {first}") + defer(ip, f"link del {ms0}") + with ksft_raises(CmdExitFailure): + ip(f"link add link {cfg.ifname} {ms1} type macsec " + f"{second.format(sci=sci)}") + # Clean up if the kernel incorrectly accepted the duplicate. + defer(ip, f"link del {ms1}") + + +def test_undefined_sci(cfg) -> None: + """An undefined SCI still selects the default when it is available.""" + + _require_ip_macsec() + ms0 = _macsec_name(0) + ms1 = _macsec_name(1) + sci = _get_mac(cfg.ifname).replace(":", "") + "0001" + + # A different port on the same lower device must not block the fallback. + ip(f"link add link {cfg.ifname} {ms0} type macsec port 2") + defer(ip, f"link del {ms0}") + ip(f"link add link {cfg.ifname} {ms1} type macsec sci ffffffffffffffff") + cleanup = defer(ip, f"link del {ms1}") + info = ip(f"-d link show dev {ms1}", json=True)[0] + ksft_eq(info["linkinfo"]["info_data"]["sci"], sci) + + # Deleting a device must make its SCI available again. + cleanup.exec() + ip(f"link add link {cfg.ifname} {ms1} type macsec sci ffffffffffffffff") + defer(ip, f"link del {ms1}") + + def _check_nsim_vid(cfg, vid, expected) -> None: """Checks if a VLAN is present. Only works on netdevsim."""
@@ -333,6 +382,8 @@ def main() -> None: test_max_secy, test_max_sc, test_offload_state, + test_duplicate_sci, + test_undefined_sci, test_vlan, test_vlan_toggle, ], args=(cfg,))
--- base-commit: 11536ee3d3e0b1bd35b6f3f8df55a6053eb0c71d change-id: 20260926-fix-macsec-duplicate-sci-ed7635ac1c35 Best regards, -- Haseeb Malik [off-list ref]