Seccomp is often described as a filter on system calls. That description works until an application uses io_uring, where a process can submit asynchronous operations through a ring instead of making one visible syscall for every file or network action. A policy that blocks openat but permits ring submission has not necessarily blocked the operation. The rule set must account for the interface that carries the work.
io_uring uses shared memory rings to submit operations and report completions. A program sets up the ring with io_uring_setup, maps shared buffers, submits work, and waits for results. The kernel performs operations on the process's behalf, subject to whatever restrictions the kernel and the ring allow. The security question is therefore both syscall-level and object-level: can this process create or use a ring, and what may the ring do?
Look past the syscall table
A common container or service policy denies a long list of dangerous syscalls and allows the ones the application currently needs. New asynchronous interfaces can invalidate the assumption that each operation has a simple one-to-one syscall signature. Auditd has separate behavior for file opens performed through io_uring, and seccomp filters see the ring interface even when the submitted operation would map to a different code path.
This does not mean every io_uring operation bypasses every control. The kernel supports ring restrictions and filters, and container runtimes and seccomp libraries may expose additional controls. The point is to test the deployed policy rather than infer it from a generic baseline. A rule generated for an older runtime can be technically valid while failing to constrain a new subsystem.
Decide who needs asynchronous I/O
Most application servers can use normal blocking or nonblocking I/O without direct io_uring access. High-performance databases, proxies, storage services, and some runtimes may need it for performance. Separate those workloads from general-purpose containers and treat ring access as an explicit capability.
The decision has several parts:
Record whether the workload creates a ring during normal operation.
Determine which operations it submits and which credentials, directories, files, and sockets those operations reach.
Deny unprivileged ring creation where the workload has no documented need.
Where ring use is required, apply the supported ring restrictions and test denied operations.
Run the workload with the least file, network, and mount authority needed if a ring operation is accepted.
Monitor creation and restriction changes as security-relevant events, not routine noise.
Do not test only the application's start-up path. Exercise uploads, cache writes, database spills, socket timeouts, and error recovery, because those paths may switch from ordinary syscalls to asynchronous operations.
Treat verifier and restriction support as versioned
The Linux kernel has accumulated changes around io_uring restrictions, credential behavior, and tracing. A policy that was correct for one kernel and runtime may not be interpreted the same way after an upgrade. Pin the security-sensitive versions in the test plan, and include the seccomp profile, runtime configuration, kernel build options, and capability set in the evidence.
If an application cannot function with ring creation denied, do not respond by granting a broad set of missing syscalls. Start with the smallest documented exception, then test the resulting authority from inside the workload. Attempt to open a path outside the allowed directory, connect to an unapproved address, and invoke an operation that should be restricted. Preserve both the policy and the observed failure.
Build a verification routine
A useful verification workflow has three layers. First, inspect the effective seccomp profile and confirm that io_uring_setup, io_uring_enter, and related calls are either denied or intentionally allowed. Second, inspect the runtime's cgroup and capability settings. Third, exercise the application under a test account and compare the operations it actually performs with the operations the policy claims to allow.
This catches a recurring policy failure: a team blocks a syscall but leaves an alternate interface open, then reports the workload as sandboxed because the application still starts. The workload starts because it found the path that remains.
io_uring is a legitimate high-performance facility and not an automatic vulnerability. It changes where the security boundary is observed. A seccomp policy should state the intended authority, not merely reproduce a list copied from another service. When the ring is unnecessary, deny it. When it is necessary, constrain it, test it, and record the decision.