CVE-2026-98922 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
net: emac: move setting of netops to fix crash
fixes the following crash on driver initialization:
|BUG: Kernel NULL pointer dereference on read at 0x00000158 |Faulting instruction address: 0xc0566b40 |Oops: Kernel access of bad area, sig: 11 [#1]
|BE PAGE_SIZE=4K PowerPC 44x Platform |Modules linked in: |CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Tainted: GW 7.3.0-rc3+ #1 |Tainted: [W]=WARN
|Hardware name: MyBook Live APM821XX 0x12c41c83 PowerPC 44x Platform |NIP: c0566b40 LR: c05648f8 CTR: c04c1e9c |REGS: c1053a20 TRAP: 0300 Tainted: GW (7.3.0-rc3+) |MSR: 0002b000 <CE,EE,FP,ME> CR: 24008808 XER: 00000000 |DEAR: 00000158 ESR: 00000000 |GPR00: c05648f8 c1053b10 c1063600 c1030000 c5ab3000 00000000 [...]
|GPR08: 00000002 00000000 00000000 c1053b40 84002808 00000000 [...]
|GPR16: cfffd210 00000002 c0beafcc cfffc960 00000000 c1030644 [...]
|GPR24: c0beafbc c1037000 00000000 0000000a 00000000 c1030000 [...]
|NIP [c0566b40] phy_link_topo_add_phy+0x2c/0x1d0
|LR [c05648f8] phy_attach_direct+0x1a4/0x368
|Call Trace: |[c1053b10] [c0811e04] klist_put+0x54/0xb4 (unreliable)
|[c1053b40] [c05648f8] phy_attach_direct+0x1a4/0x368
|[c1053b70] [c0564ae8] phy_connect_direct+0x2c/0x60
|[c1053b90] [c056c7a8] of_phy_connect+0x50/0x74
|[c1053bc0] [c0572a88] emac_probe+0xd50/0x119c
|[c1053c90] [c04cb770] platform_probe+0x74/0xa4
|[c1053cb0] [c04c8f08] really_probe+0x120/0x2b0
|[c1053cd0] [c04c9254] __driver_probe_device+0x1bc/0x1fc
|[c1053d00] [c04c9334] driver_probe_device+0x38/0xa8
|[c1053d30] [c04c9560] __driver_attach+0xf4/0x10c
|[c1053d50] [c04c6af8] bus_for_each_dev+0x68/0xd0
|[c1053d90] [c04c7c34] bus_add_driver+0xcc/0x1ec
|[c1053dc0] [c04c9f6c] driver_register+0xcc/0x110
|[c1053de0] [c0aa3f40] emac_init+0x1c4/0x200
This bug showed up starting with v7.3-rc1. At the NIP in phy_link_topo_add_phy() is a netdev_need_ops_lock() check. This was added by the following commit ded86da4bbb7 ("net: ethtool: relax ethnl_req_get_phydev() locking assertion")
The bug shows up because at the time of_phy_connect() was called, the netdev_ops were *not yet* determined. My fix is to move the code that sets netdev_ops+commac.ops+ethtool_ops further up as emac_init_config() derives that by looking at the device-tree and sets the required dev->phy_mode accordingly.
During review, the Sashiko bot's AI stated that the commac assignment became a dead store. Great catch! To keep the original behavior as-is, one mentioned option "set dev->commac.ops = &emac_commac_ops only in the non-gige case?" sounded like a great plan. So the dev->commac.ops assignment for the non-gige-case moves into the else block.
This patch was tested on a WD MyBook Live (RGMII). the device now works again.
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Analysis
by VulDB Data Team • 10/23/2026
The Linux kernel vulnerability identified in the Ethernet Media Access Controller driver involves a critical NULL pointer dereference that occurs during the initialization phase of the network interface. This flaw manifests as a kernel oops with signal eleven, indicating an access to bad memory area at address zero plus offset one hundred fifty-eight hex on PowerPC 44x platforms such as the WD MyBook Live device running APM821XX hardware. The crash is triggered specifically when the phy_link_topo_add_phy function attempts to execute a netdev_need_ops_lock check, which relies on valid network device operations being present in memory. Because these operations are not yet initialized at that specific point in the execution flow, the kernel dereferences a NULL pointer, leading to an immediate system crash or instability during driver probe routines.
The root cause of this vulnerability lies in the ordering of initialization steps within the emac_probe function relative to phy_connect_direct calls. The issue was introduced by commit ded86da4bbb7 which relaxed locking assertions for ethnl_req_get_phydev but inadvertently created a race condition where network device operations were accessed before they were fully configured. Specifically, when phy_attach_direct and subsequent functions are invoked, the netdev_ops structure has not yet been populated with valid function pointers derived from the device tree configuration. This temporal mismatch means that any code path attempting to validate or utilize these operations will encounter a NULL reference since the pointer remains uninitialized until later in the initialization sequence where emac_init_config is supposed to set dev->phy_mode and associated operation structures.
From a technical perspective, this flaw represents a classic case of improper resource ordering leading to use-before-initialization errors. The vulnerability aligns with CWE-476 which describes NULL Pointer Dereference vulnerabilities resulting from accessing memory through an uninitialized or null pointer. In the context of operating system security, this type of defect can be leveraged for denial of service attacks if triggered by local users who can influence device enumeration timing, although in most embedded scenarios it simply results in boot failures rather than exploitable conditions. The ATT&CK framework categorizes such kernel-level crashes under techniques that disrupt availability, particularly those involving exploitation of software flaws to cause system instability or crash during startup processes where no user interaction is required for the initial trigger but may require physical access or specific hardware configurations to reproduce consistently.
The resolution involves restructuring the initialization sequence within the emac driver code by moving the assignment of netdev_ops, commac.ops, and ethtool_ops earlier in the probe function before any PHY connection attempts are made. This ensures that when phy_connect_direct is called, all necessary operation structures are already populated with valid data derived from device tree parsing via emac_init_config. Additionally, code review identified a dead store issue regarding the commac assignment which was optimized by conditionally setting dev->commac.ops only in non-gigabit cases to preserve original behavior while eliminating redundant writes. This patch has been validated on WD MyBook Live hardware using RGMII interfaces confirming that restoring proper initialization order resolves the crash and allows normal network interface operation without kernel panics during boot sequences.
Mitigation strategies for this vulnerability primarily involve applying the upstream kernel patch that corrects the initialization ordering in the emac driver module. System administrators managing embedded devices based on PowerPC 44x architecture should ensure their firmware includes updates containing commit fixes related to net device operations setup prior to PHY attachment routines. For organizations unable to immediately update kernels, disabling automatic network interface activation during early boot stages or manually loading drivers after core subsystems are fully initialized may serve as a temporary workaround though this is often impractical in embedded environments where driver probing occurs automatically via platform bus mechanisms. Long-term resilience requires rigorous static analysis tools and runtime verification checks that validate pointer validity before dereferencing operations especially within critical initialization paths where timing dependencies between hardware abstraction layers must be strictly maintained to prevent similar use-before-initialization defects across other network drivers.