CVE-2026-72493

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

net: serialize netifrunning() check in enqueueto_backlog()

Syzbot reported a KASAN slab-use-after-free in fibruleslookup().

The root cause is a race condition where packets can escape the backlog

flushing during device unregistration (e.g., during netns exit).

Commit e9e4dd3267d0 ("net: do not process device backlog during unregistration")

introduced a lockless netifrunning() check in enqueueto_backlog() to

prevent queuing packets to an unregistering device.

However, this creates a TOCTOU race window.

A lockless transmitter (like veth_xmit) can pass

the check before devclose() clears IFFUP. If the transmitter is then

delayed, flushallbacklogs() can run and finish before the transmitter

grabs the backlog lock and queues the packet. The packet then escapes

the flush and triggers UAF later when processed.

Fix this by moving the netif_running() check inside the backlog lock.

This serializes the check with the flush work (which also grabs the lock).

We then either queue the packet before the flush runs (so it gets flushed),

or check netif_running() after the flush/close completes (so it gets dropped).