In the Linux kernel, the following vulnerability has been resolved:
ethtool: Fix uninitialized number of lanes
It is not possible to set the number of lanes when setting link modes using the legacy IOCTL ethtool interface. Since 'struct ethtool_link_ksettings' is not initialized in this path, drivers receive an uninitialized number of lanes in 'struct ethtool_link_ksettings::lanes'.
When this information is later queried from drivers, it results in the ethtool code making decisions based on uninitialized memory, leading to the following KMSAN splat [1]. In practice, this most likely only happens with the tun driver that simply returns whatever it got in the set operation.
As far as I can tell, this uninitialized memory is not leaked to user space thanks to the 'ethtool_ops->cap_link_lanes_supported' check in linkmodes_prepare_data().
Fix by initializing the structure in the IOCTL path. Did not find any more call sites that pass an uninitialized structure when calling 'ethtool_ops::set_link_ksettings()'.
[1] BUG: KMSAN: uninit-value in ethnl_update_linkmodes net/ethtool/linkmodes.c:273 [inline] BUG: KMSAN: uninit-value in ethnl_set_linkmodes+0x190b/0x19d0 net/ethtool/linkmodes.c:333 ethnl_update_linkmodes net/ethtool/linkmodes.c:273 [inline] ethnl_set_linkmodes+0x190b/0x19d0 net/ethtool/linkmodes.c:333 ethnl_default_set_doit+0x88d/0xde0 net/ethtool/netlink.c:640 genl_family_rcv_msg_doit net/netlink/genetlink.c:968 [inline] genl_family_rcv_msg net/netlink/genetlink.c:1048 [inline] genl_rcv_msg+0x141a/0x14c0 net/netlink/genetlink.c:1065 netlink_rcv_skb+0x3f8/0x750 net/netlink/af_netlink.c:2577 genl_rcv+0x40/0x60 net/netlink/genetlink.c:1076 netlink_unicast_kernel net/netlink/af_netlink.c:1339 [inline] netlink_unicast+0xf41/0x1270 net/netlink/af_netlink.c:1365 netlink_sendmsg+0x127d/0x1430 net/netlink/af_netlink.c:1942 sock_sendmsg_nosec net/socket.c:724 [inline] sock_sendmsg net/socket.c:747 [inline] ____sys_sendmsg+0xa24/0xe40 net/socket.c:2501 ___sys_sendmsg+0x2a1/0x3f0 net/socket.c:2555 __sys_sendmsg net/socket.c:2584 [inline] __do_sys_sendmsg net/socket.c:2593 [inline] __se_sys_sendmsg net/socket.c:2591 [inline] __x64_sys_sendmsg+0x36b/0x540 net/socket.c:2591 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd
Uninit was stored to memory at: tun_get_link_ksettings+0x37/0x60 drivers/net/tun.c:3544 __ethtool_get_link_ksettings+0x17b/0x260 net/ethtool/ioctl.c:441 ethnl_set_linkmodes+0xee/0x19d0 net/ethtool/linkmodes.c:327 ethnl_default_set_doit+0x88d/0xde0 net/ethtool/netlink.c:640 genl_family_rcv_msg_doit net/netlink/genetlink.c:968 [inline] genl_family_rcv_msg net/netlink/genetlink.c:1048 [inline] genl_rcv_msg+0x141a/0x14c0 net/netlink/genetlink.c:1065 netlink_rcv_skb+0x3f8/0x750 net/netlink/af_netlink.c:2577 genl_rcv+0x40/0x60 net/netlink/genetlink.c:1076 netlink_unicast_kernel net/netlink/af_netlink.c:1339 [inline] netlink_unicast+0xf41/0x1270 net/netlink/af_netlink.c:1365 netlink_sendmsg+0x127d/0x1430 net/netlink/af_netlink.c:1942 sock_sendmsg_nosec net/socket.c:724 [inline] sock_sendmsg net/socket.c:747 [inline] ____sys_sendmsg+0xa24/0xe40 net/socket.c:2501 ___sys_sendmsg+0x2a1/0x3f0 net/socket.c:2555 __sys_sendmsg net/socket.c:2584 [inline] __do_sys_sendmsg net/socket.c:2593 [inline] __se_sys_sendmsg net/socket.c:2591 [inline] __x64_sys_sendmsg+0x36b/0x540 net/socket.c:2591 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd
Uninit was stored to memory at: tun_set_link_ksettings+0x37/0x60 drivers/net/tun.c:3553 ethtool_set_link_ksettings+0x600/0x690 net/ethtool/ioctl.c:609 __dev_ethtool net/ethtool/ioctl.c:3024 [inline] dev_ethtool+0x1db9/0x2a70 net/ethtool/ioctl.c:3078 dev_ioctl+0xb07/0x1270 net/core/dev_ioctl.c:524 sock_do_ioctl+0x295/0x540 net/socket.c:1213 sock_i ---truncated---
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Amazon Linux Ami 2 | — | Upgrade kernel-develUpgrade kernel-debuginfoUpgrade kernel-headersUpgrade python-perf-debuginfoUpgrade perfUpgrade kernelUpgrade kernel-tools-develUpgrade kernel-livepatch-5.15.117-72.142Upgrade kernel-tools-debuginfoUpgrade kernel-debuginfo-common-x86_64Upgrade perf-debuginfoUpgrade kernel-debuginfo-common-aarch64Upgrade python-perfUpgrade bpftool-debuginfoUpgrade kernel-toolsUpgrade bpftool | May 20, 2026 | May 20, 2026 |
| Amazon_linux_2023 | — | Upgrade kernel-develUpgrade kernel-libbpfUpgrade kernel-livepatch-6.1.29-47.49Upgrade kernel-tools-debuginfoUpgrade kernel-libbpf-staticUpgrade bpftoolUpgrade kernel-debuginfoUpgrade kernel-tools-develUpgrade python3-perfUpgrade kernel-libbpf-develUpgrade kernelUpgrade kernel-headersUpgrade bpftool-debuginfoUpgrade kernel-toolsUpgrade kernel-debuginfo-common-x86_64Upgrade perf-debuginfoUpgrade perfUpgrade kernel-debuginfo-common-aarch64Upgrade python3-perf-debuginfo | Jan 12, 2026 | Dec 9, 2025 |
| Debian | — | Upgrade linux | Dec 10, 2025 | Dec 10, 2025 |
| Redhat_linux | — | No solution exists | Jul 17, 2026 | Dec 9, 2025 |
| Ubuntu | — | Upgrade linux-realtimeUpgrade linux-nvidia-tegraUpgrade linux-bluefieldUpgrade linuxUpgrade linux-aws-5.15Upgrade linux-raspiUpgrade linux-intel-iot-realtimeUpgrade linux-lowlatency-hwe-5.15Upgrade linux-gcpUpgrade linux-nvidia-tegra-5.15Upgrade linux-awsUpgrade linux-azureUpgrade linux-intel-iotg-5.15Upgrade linux-ibm-5.15Upgrade linux-gkeopUpgrade linux-gcp-5.15Upgrade linux-intel-iotgUpgrade linux-ibmUpgrade linux-oracle-5.15Upgrade linux-nvidia-tegra-igxUpgrade linux-riscv-5.15Upgrade linux-lowlatencyUpgrade linux-gkeUpgrade linux-hwe-5.15Upgrade linux-oracleUpgrade linux-kvmUpgrade linux-nvidiaUpgrade linux-azure-5.15Upgrade linux-xilinx-zynqmp | Dec 11, 2025 | Dec 9, 2025 |
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