CVE-2026-72322

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

ipv6: mcast: Fix potential UAF in MLD delayed work

A race condition exists between device teardown and incoming MLD query

processing, leading to a Use-After-Free in the MLD delayed work.

During device destruction, the primary reference to inet6_dev is dropped,

which can drop its refcount to 0. The actual freeing of inet6_dev memory

is deferred via RCU.

Concurrently, the packet receive path runs under RCU read lock and obtains

the inet6_dev pointer. Because the memory is RCU-protected, CPU-0 can

safely dereference inet6_dev even if its refcount has hit 0.

However, if CPU-0 calls igmp6eventquery() and schedules delayed work, it

attempts to acquire a reference using in6devhold(). This increments the

refcount from 0 to 1, triggering a "refcount_t: addition on 0" warning.

Since the inet6_dev memory is still scheduled to be freed after the RCU

grace period, the device is freed while the work is still scheduled.

When the work runs, it accesses the freed memory, causing a kernel panic.

Fix this by using refcountincnot_zero() (via a new helper

in6devhold_safe()) to prevent acquiring a reference if the device is

already being destroyed. If the refcount is 0, we do not schedule the work.