CVE-2026-74615

Summary

In the Linux kernel, the following vulnerability has been resolved:

vxlan: do not arm the ageing timer on a device that is down

vxlan_changelink() arms vxlan->age_timer whenever the requested ageing interval differs from the configured one:

if (conf.age_interval != vxlan->cfg.age_interval)
	mod_timer(&vxlan->age_timer, jiffies);

There is no netif_running() test, so the timer is armed even on a device that was never brought up. The only synchronous cancel in the driver is the timer_delete_sync() in vxlan_stop(), which is .ndo_stop. netif_close_many() drops devices without IFF_UP before __dev_close_many() runs, so that cancel is skipped for such a device.

vxlan_setup() sets dev->needs_free_netdev = true and age_timer is a member of struct vxlan_dev, so free_netdev() releases the allocation the timer lives in while it is still queued on a timer_base. expire_timers() unlinks the entry before it loads timer->function, so the timer core writes through the freed object's list pointers:

BUG: KASAN: slab-use-after-free in __run_timers+0x208/0x654 Write of size 8 at addr ffff00001adace68 by task true/192 __asan_store8+0x84/0xac __run_timers+0x208/0x654 run_timer_softirq+0x154/0x18c Allocated by task 189: alloc_netdev_mqs+0x64/0x720 rtnl_create_link+0x4ac/0x520 rtnl_newlink+0x758/0xd00 Freed by task 191: netdev_release+0x40/0x58 netdev_run_todo+0x4a4/0x8c0 rtnl_dellink+0x200/0x4e8

The rtnl operations involved are netns-scoped, so an unprivileged user can perform them in a new user and network namespace.

Arming the timer on a down device never had an effect: vxlan_cleanup() returns early on !netif_running(), and vxlan_open() arms the timer for any non-zero interval once the device is brought up. Add the missing test.

Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/be44d79d14d7f9ae7c8ffb7272142005341b5123
• https://git.kernel.org/stable/c/26c179d47403d2f919ee914cc02c31d896b59fee
• https://git.kernel.org/stable/c/9dc561f0522c35bdd66e0646a748814a138ec4ca
• https://git.kernel.org/stable/c/619dd29045e439d0b0f8c6d4fec1af447a050680
• https://git.kernel.org/stable/c/6b095e99b9e67ea31f0c4b00260e010898253519
• https://git.kernel.org/stable/c/46bb297ad77680e009244f067f27d51cf5b8c7cf
• https://git.kernel.org/stable/c/6b4119af544996a545cf84b16f1dbce829ba0de8
• https://git.kernel.org/stable/c/b37971686ec59fb027fa4910ba16805e68fddb97

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