NetBSD opencrypto CVE-2026-32848

The NetBSD opencrypto subsystem exposes cryptographic acceleration hardware and software via the /dev/crypto character device (cryptodev). The vulnerable code path is cryptodev_op() in sys/opencrypto/cryptodev.c, which handles the CIOCCRYPT ioctl. Prior to commit ec8451e, the csession struct embedded mutable per-operation fields - tmp_iv, tmp_mac, iovec[1], uio, and error - directly into the session-level struct. Because a csession is shared across threads by session identifier, two threads executing concurrent CIOCCRYPT on the same session ID raced on this shared mutable state. CWE-362 (Concurrent Execution Using Shared Resource with Improper Synchronization) is the root cause: the absence of reference counting and per-operation isolation on csession allowed one thread's cleanup to free buffers still in use or already freed by a concurrent thread, producing a classic double-free / use-after-free condition. The fix in commit ec8451e introduces a new cryptop_data struct (cod_ctor/cod_dtor) that isolates all per-operation state, adds a kmutex_t and volatile uint32_t refcnt to csession, and implements proper reference counting across fcrypt and csession lifecycles, including CRYPTODEV_OPS_MAX as an operation cap.