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 igmp6_event_query() and schedules delayed work, it
attempts to acquire a reference using in6_dev_hold(). 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 refcount_inc_not_zero() (via a new helper
in6_dev_hold_safe()) to prevent acquiring a reference if the device is
already being destroyed. If the refcount is 0, we do not schedule the work.

https://git.kernel.org/stable/c/0401d6cf7877c9be36652385dfcbf7f891b8b590

https://git.kernel.org/stable/c/0458ba1cda830ba4ccfcd9e19c0891438bcdbe4e

https://git.kernel.org/stable/c/9815e834f5ff8b39e0ea9f0dbd532f4a3b8f0785

https://git.kernel.org/stable/c/9b26518b6896a16b809b1e42986f4ebac7bccc1e

https://git.kernel.org/stable/c/9ce741c22df4fd9546e30306317ac7df3607e48f

https://git.kernel.org/stable/c/ebbebf6cee950d7f1c81990256c0eae9e62572ae

https://git.kernel.org/stable/c/f03b0a45535d49bdab7e502efaacee205b2a7865

https://git.kernel.org/stable/c/f12b63ef26a035c5a29b3ef56401e38199010d4a

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