Cloudanix VulnDB

CVE-2026-98302

None

CVSS

—

EPSS

0.2%

Published

Oct 6, 2026

CISA due date

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Cloudanix analysis

Schedule a fix SSVC: Track

A flaw in an old network driver can crash the entire computer if someone with admin rights tries to change a network card's address while that card is turned off.

Exploitation
Local Privilege
Attacker needs
High Privilege
Complexity
Low
Impact
Denial Of Service
Component
OS kernel
Class
Memory Corruption
Remediation
Patch
Effort
Low
Patch risk
Low

What it actually does

Unconditional call to ResetAdapter() in skfp_ctl_set_mac_address() when the FDDI interface is down dereferences NULL pointers in mac_drv_clear_tx_queue() and mac_drv_clear_rx_queue() because tx/rx queues are never initialized, producing a kernel NULL pointer dereference and oops.

Why it matters to the business

Local denial-of-service on any Linux system exposing an skfp FDDI interface to a privileged user; systems using legacy FDDI hardware face unplanned reboots or crashes when MAC address changes are attempted while the interface is administratively down.

How an attack unfolds

An attacker with CAP_NET_ADMIN uses ip link or equivalent to set a new MAC address on a down skfp FDDI interface; the ndo_set_mac_address handler invokes ResetAdapter() without a netif_running() guard, causing card_stop() followed by a loop that dereferences uninitialized queue pointers and crashes the kernel.

How to fix it

Apply the upstream fix that adds a netif_running() guard before ResetAdapter() in skfp_ctl_set_mac_address(); rebuild and boot the patched kernel. No specific fixed versions are listed for downstream distributions; backport the guard or disable the skfp driver if FDDI hardware is not required.

How to confirm the fix worked

Confirm the patch by inspecting skfp_ctl_set_mac_address() for an early return when !netif_running(); attempt the MAC address change on a down interface in a test kernel and verify absence of the KASAN null-ptr-deref in mac_drv_clear_tx_queue.

Typical attack path

  1. Obtain CAP_NET_ADMIN on the target host
  2. Ensure the target skfp FDDI interface is administratively down
  3. Execute ip link set dev <fddi> address <new-mac>
  4. Trigger unconditional ResetAdapter() path in skfp_ctl_set_mac_address
  5. Dereference NULL tx_curr_get / rx pointers inside mac_drv_clear_*_queue

How to detect it

Search kernel logs and crash dumps for the exact call trace containing mac_drv_clear_tx_queue+0x68, ResetAdapter, and skfp_ctl_set_mac_address; correlate with audit logs showing ip link or netlink setlink operations on FDDI interfaces immediately preceding the oops.

  • BUG: KASAN: null-ptr-deref in mac_drv_clear_tx_queue
  • mac_drv_clear_tx_queue+0x68/0x2c0 [skfp]
  • ResetAdapter+0x29/0x100 [skfp]
  • skfp_ctl_set_mac_address+0x57/0x80 [skfp]

What your security team should do

  • Prioritize patching any kernel that includes the skfp driver and is reachable by untrusted local users
  • Audit systems for presence of the skfp module and legacy FDDI adapters; remove the driver if unused
  • Monitor for kernel oops reports containing mac_drv_clear_tx_queue and skfp symbols
  • Enforce least-privilege for CAP_NET_ADMIN to reduce attack surface

The record

In the Linux kernel, the following vulnerability has been resolved: net: fddi: skfp: fix NULL deref when setting the MAC address while down skfp_ctl_set_mac_address() calls ResetAdapter() unconditionally, without checking netif_running(). ResetAdapter() first calls card_stop(), which sets smc->hw.hw_state to STOPPED, and then mac_drv_clear_tx_queue(), which walks the two transmit queues: for (i = QUEUE_S; i <= QUEUE_A0; i++) { queue = smc->hw.fp.tx[i] ; ... t = queue->tx_curr_get ; smc->hw.fp.tx[] is only populated by init_tx(), which is reached from skfp_open() through init_smt() -> init_fddi_driver() -> init_fplus() -> init_mac() -> init_tx(). The private area is allocated and zeroed by alloc_fddidev(), so on an interface that has never been brought up both queue pointers are still NULL. The hw_state test at the top of mac_drv_clear_tx_queue() does not catch this, because card_stop() has just set STOPPED; the function proceeds into the loop and dereferences NULL. ResetAdapter() does call init_smt() itself, but only after the queues have been cleared. Setting the MAC address on a down interface therefore oopses: ip link set dev fddi0 address 02:00:00:00:00:01 BUG: KASAN: null-ptr-deref in mac_drv_clear_tx_queue+0x68/0x2c0 [skfp] Read of size 8 at addr 0000000000000010 by task ip/302 Call Trace: <TASK> mac_drv_clear_tx_queue+0x68/0x2c0 [skfp 6c01d4bab63c36978bd0a7d7e90837adb44cc37b] ResetAdapter+0x29/0x100 [skfp 6c01d4bab63c36978bd0a7d7e90837adb44cc37b] skfp_ctl_set_mac_address+0x57/0x80 [skfp 6c01d4bab63c36978bd0a7d7e90837adb44cc37b] netif_set_mac_address+0x1e4/0x2c0 do_setlink+0x684/0x2680 </TASK> Address 0x10 is the offset of tx_curr_get, the third pointer in struct s_smt_tx_queue, on 64-bit. mac_drv_clear_rx_queue(), which ResetAdapter() calls immediately afterwards, dereferences smc->hw.fp.rx[QUEUE_R1] in the same way behind the same ineffective hw_state test; the transmit queue merely crashes first. Both are covered by the guard below. Skip the adapter reset when the interface is down. dev_addr_set() is left unconditional, so the new address is still recorded in dev->dev_addr. Nothing is lost by not resetting the adapter here: skfp_open() deliberately re-reads the factory address on every open, read_address(smc, NULL); eth_hw_addr_set(dev, smc->hw.fddi_canon_addr.a); and the comment above it states this is done to discard exactly such an address override across a close/open cycle. An address set while the interface is down could not have survived the following open even before this change, so the guard removes no working behaviour. Guarding the hardware side of ndo_set_mac_address() with netif_running() is established practice; skge_set_mac_address() has done so since commit 2eb3e621c4e0 ("skge: set mac address bonding fix"). Guarding the reset as a whole, rather than NULL-checking the queues, is also what the rest of the driver expects. After a previous open/close the queue pointers are stale but non-NULL, so there is no crash, yet ResetAdapter() goes on to call smt_online() and STI_FBI() ("Enable Board Interrupts") while skfp_close() has already called free_irq() - the adapter would be brought back online with no handler installed. The only other ResetAdapter() caller is skfp_interrupt(), which by construction runs only while the device is open. Found by automated driver testing against an emulated SysKonnect FDDI adapter under a KASAN-enabled 7.0.0 kernel. Triggering it requires CAP_NET_ADMIN.

Affected packages

Ecosystem Package Introduced Fixed