CVE-2026-12233: Uninitialized mutex in TLS trusted-credential backend causes kernel NULL-deref DoS under contention

The PSA Protected Storage credential backend (subsys/net/lib/tlscredentials/tlscredentialstrusted.c) declared its credential-store mutex as a plain zero-filled static struct kmutex credentiallock; and never called kmutexinit() on it. A statically zero-filled kmutex has an uninitialized wait queue (its dlist head/tail are NULL instead of the self-referential sentinels that kmutexinit/KMUTEXDEFINE install). The uncontended lock path does not touch the wait queue, so the defect is latent and serialized use behaves correctly.

When two execution contexts contend on the lock, kmutexlock() pends the blocking thread on the wait queue via zpendcurr(), which calls sysdlistappend() on the zeroed list and dereferences a NULL tail pointer (tail->next = node), faulting the kernel. The lock is held during TLS handshake credential loading and by all credential add/get/delete operations, so a deployment performing concurrent TLS handshakes (for example a server handling multiple simultaneous connections from a remote peer) or a credential-management operation concurrent with a handshake can trigger the dereference.

The impact is a denial of service: a deterministic kernel panic / device reset on the first contention. There is no memory corruption beyond the NULL dereference and no confidentiality or integrity impact; mutual exclusion on the fast path remains correct. Exposure is limited to builds with CONFIGTLSCREDENTIALSBACKENDPROTECTEDSTORAGE enabled (PSA Protected Storage / TF-M platforms); the default volatile RAM backend initializes its lock correctly and is unaffected.

The fix initializes the mutex statically with KMUTEXDEFINE(credentiallock), providing a valid wait queue so the contended path no longer touches a NULL list.