CVE-2025-21652 — ipvlan: Fix use-after-free in ipvlan_get_iflink().

Affected: Linux

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

ipvlan: Fix use-after-free in ipvlan_get_iflink().

syzbot presented an use-after-free report [0] regarding ipvlan and linkwatch.

ipvlan does not hold a refcnt of the lower device unlike vlan and macvlan.

If the linkwatch work is triggered for the ipvlan dev, the lower dev might have already been freed, resulting in UAF of ipvlan->phy_dev in ipvlan_get_iflink().

We can delay the lower dev unregistration like vlan and macvlan by holding the lower dev's refcnt in dev->netdev_ops->ndo_init() and releasing it in dev->priv_destructor().

Jakub pointed out calling .ndo_XXX after unregister_netdevice() has returned is error prone and suggested [1] addressing this UAF in the core by taking commit 750e51603395 ("net: avoid potential UAF in default_operstate()") further.

Let's assume unregistering devices DOWN and use RCU protection in default_operstate() not to race with the device unregistration.

[0]: BUG: KASAN: slab-use-after-free in ipvlan_get_iflink+0x84/0x88 drivers/net/ipvlan/ipvlan_main.c:353 Read of size 4 at addr ffff0000d768c0e0 by task kworker/u8:35/6944

CPU: 0 UID: 0 PID: 6944 Comm: kworker/u8:35 Not tainted 6.13.0-rc2-g9bc5c9515b48 #12 4c3cb9e8b4565456f6a355f312ff91f4f29b3c47 Hardware name: linux,dummy-virt (DT) Workqueue: events_unbound linkwatch_event Call trace: show_stack+0x38/0x50 arch/arm64/kernel/stacktrace.c:484 (C) __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0xbc/0x108 li…

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CVE-2025-21652 — ipvlan: Fix use-after-free in ipvlan_get_iflink().