Kernel Security on Nalar

io_uring Restrictions Freeze an Allowed Operation Surface Before Ring Activation

Fri, 18 Sep 2026 00:00:00 +0000

A service can expose an io_uring instance to code that should perform only a narrow class of asynchronous operations. The ring itself, however, supports many submission opcodes and registration commands. Relying only on application code to avoid unwanted operations leaves the allowed surface as a convention rather than a kernel-enforced property.

Linux provides a tighter mechanism through IORING_REGISTER_RESTRICTIONS. A ring created with IORING_SETUP_R_DISABLED can receive a restriction set before it becomes usable for submissions. The process then enables the ring with IORING_REGISTER_ENABLE_RINGS. From that point, the kernel evaluates operations against the registered restrictions.

Landlock Rulesets Add a Process-Scoped Filesystem Access Boundary

Fri, 18 Sep 2026 00:00:00 +0000

A service can begin with ordinary filesystem permissions that are broader than the files it needs during steady-state operation. Changing ownership or mount topology may be impractical because the same host resources are shared with other processes. Linux Landlock addresses this gap by letting a process add a kernel-enforced access restriction to itself and, through inheritance, to descendants.

Landlock is a Linux Security Module designed for sandboxing. Its rules do not grant filesystem access that DAC, ACLs, capabilities, or another security mechanism would otherwise deny. They add another authorization layer. An operation succeeds only when the other applicable controls and the Landlock policy permit it.

Seccomp User Notification Moves Selected System Calls Behind a Supervisor Decision

Fri, 18 Sep 2026 00:00:00 +0000

A sandboxed process may need an operation that cannot be represented safely as a permanent seccomp allow rule. The operation can depend on runtime policy, external state, or a resource that only a more privileged component should inspect. Allowing the system call unconditionally widens the sandbox, while rejecting it removes required functionality.

Linux seccomp user notification provides a mediation point for this case. A seccomp filter can return SECCOMP_RET_USER_NOTIF for selected calls. The kernel then blocks the triggering task and emits a notification through a listener file descriptor. A supervisor reads that notification and sends a response that determines the immediate disposition of the intercepted call.