CVE-2023-53798
Description
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---
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
In the Linux kernel, the legacy IOCTL ethtool interface fails to initialize the 'lanes' field in 'struct ethtool_link_ksettings', leading to uninitialized memory usage and potential KMSAN splats.
Vulnerability
Overview
CVE-2023-53798 is a vulnerability in the Linux kernel's ethtool subsystem. The root cause is that when setting link modes via the legacy IOCTL interface, the struct ethtool_link_ksettings is not fully initialized. Specifically, the lanes field remains uninitialized, and drivers receive this uninitialized value. When drivers later return this information, the ethtool code makes decisions based on uninitialized memory, which can trigger a KMSAN (Kernel Memory Sanitizer) splat [1].
Exploitation and
Attack Surface
This issue is triggered through the legacy IOCTL ethtool interface, which does not initialize the lanes field. The attack surface is local, requiring the ability to issue ethtool commands. In practice, the tun driver is most likely to expose this behavior because it simply returns whatever value it received during the set operation [1]. No special privileges beyond the ability to use ethtool are required, but the impact is primarily a kernel memory corruption or information leak, though the uninitialized memory is not directly leaked to user space due to a check in linkmodes_prepare_data() [1].
Impact
An attacker who can trigger this path may cause the kernel to operate on uninitialized memory, leading to unpredictable behavior, including kernel crashes or potential privilege escalation. The KMSAN splat indicates that the kernel detects the use of uninitialized values, which could be exploited to corrupt kernel state [1].
Mitigation
The fix initializes the struct ethtool_link_ksettings in the IOCTL path to ensure the lanes field is set to a known value. The patch has been applied to the stable kernel branches [1][2]. Users should update their kernels to include the fix.
AI Insight generated on May 19, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.
Affected products
2Patches
5da81af0ef809942a2a0184f76456d80045d672808c4ab5fd9ad685dbfe7eVulnerability mechanics
Generated on May 9, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.
References
5- git.kernel.org/stable/c/6456d80045d6de47734b1a3879c91f72af186529nvd
- git.kernel.org/stable/c/72808c4ab5fd01bf1214195005e15b434bf55cefnvd
- git.kernel.org/stable/c/942a2a0184f7bb1c1ae4bbc556559c86c054b0d2nvd
- git.kernel.org/stable/c/9ad685dbfe7e856bbf17a7177b64676d324d6ed7nvd
- git.kernel.org/stable/c/da81af0ef8092ecacd87fac3229c29e2e0ce39fdnvd
News mentions
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