CVE-2026-11742: Use-after-free race in kernel `k_queue_peek_head/tail` due to missing spinlock

The kernel queue helper zqueuenodepeek() in kernel/queue.c dereferences a node taken from a queue's dataq list, reading the node's flag byte and, for items enqueued via kqueueallocappend/allocprepend, the data pointer of an internally allocated allocnode struct. The implementations of zimplkqueuepeekhead() and zimplkqueuepeektail() performed this read-and-dereference without holding the queue's spinlock, while every other accessor of the same list — including kqueueget(), which unlinks a node and kfree()s its backing allocnode — operates under that lock.

Because peek was unsynchronized, a concurrent kqueueget() on the same queue (on an SMP build, or under preemption/ISR concurrency) can free the node between the moment peek obtains the node pointer and the moment it dereferences it. The peek then reads flag bits and a data pointer out of freed, potentially re-allocated heap memory and returns a stale or dangling pointer to its caller. kfifo and klifo are thin wrappers over kqueue, so this affects buffer queues used throughout the netbuf, Bluetooth, USB, and networking subsystems; the peek operations are also system calls reachable from CONFIGUSERSPACE threads.

The consequences are a use-after-free read that can leak stale heap contents (one pointer word) and, when the returned dangling pointer is subsequently consumed as a live buffer, a dereference that can crash the system or corrupt memory. Exploitation requires winning a small race window with local access (e.g. a userspace process racing kqueuepeek against kqueueget on a shared queue, or two CPUs), so practical impact is bounded and of low severity.

The fix wraps both peek implementations with kspinlock/kspinunlock on the queue lock, making the read-and-dereference atomic with respect to the concurrent unlink-and-free and bringing peek into line with the rest of the queue's locking discipline.