Open vSwitch — CWE-407 Disclosure Brief

2026-03-27 · Patch available — awaiting upstream merge

Finding

One defect with two instances in Open vSwitch's datapath interface offload module. A LIST_FOR_EACH provider name scan and a duplicate port scan both execute on the per-port-add hot path using linear list traversal. Fix: HashMap<name, provider> index. Patched.

The Defects

ovs-0001 (PATCHED — HIGH): lib/dpif-offload.c:580,229

/* Line 580 — per port-add: provider lookup by name O(T×P) */
LIST_FOR_EACH(provider, node, &dpif_offload_providers) {
    if (!strcmp(provider->name, type)) {   /* O(P) provider scan per port-add */
        break;
    }
}

/* Line 229 — per port-add: duplicate scan O(P) */
LIST_FOR_EACH(existing, node, &dpif_offload_providers) {
    if (!strcmp(existing->name, provider->name)) {  /* O(P) dup check */
        return EEXIST;
    }
}
/* Combined: O(T×P) for T port-add events × P registered providers */

At line 580, every port-add event performs a LIST_FOR_EACH walk over P registered offload providers comparing names with strcmp. At line 229, every provider registration performs a duplicate check with the same linear walk. For T port-add events and P providers: O(T × P) comparisons at line 580; O(P) per registration at line 229. Fix: shash (OVS string hash map) indexed by provider name → O(1) lookups at both sites.

Complexity Proof

Let P = number of registered dpif offload providers, T = number of port-add events processed per second.

Line 580 (per port-add):

Defective: LIST_FOR_EACH walks all P providers doing strcmp until the matching name is found.
- Average case: P/2 comparisons per port-add → O(T × P) per second.
- Worst case (provider not found or last in list): P comparisons per port-add.
Fixed: shash_find(&offload_provider_map, type) → O(1) per port-add → O(T) per second.
At P=T=10 providers with 100 port-add/sec: defective=500 strcmp/sec, fixed=100 hash lookups/sec.

Line 229 (per registration):

Defective: O(P) walk per dpif_offload_provider_register() call.
Fixed: shash_find → O(1) dup check.

In OVS deployments with hardware offload (SmartNICs, SR-IOV), the number of port-add events is high — every VM/container network interface attachment triggers one. The provider scan at line 580 is in the critical path for datapath setup latency.

At P=50 providers in a large deployment: 50× reduction in strcmp work per port-add.

Impact

All Open vSwitch deployments using dpif hardware offload — including OVN deployments on hypervisors with SmartNIC offload, OpenStack/Neutron deployments with OVS-DPDK, and Kubernetes nodes with OVS-based CNI plugins (e.g., OVN-Kubernetes, Antrea). Port-add events fire on every virtual interface attachment — VM boot, container creation, live migration endpoint setup. The defect adds linear latency to each such event proportional to the number of registered offload providers.

Open vSwitch is the dominant software-defined networking switch in cloud infrastructure, deployed in OpenStack, Red Hat OpenShift, and major public cloud data planes.

The Fix

Replace the dpif_offload_providers linked list with an shash (OVS string hash map) for O(1) name-based lookup and duplicate detection:

/* Before — line 580 (provider lookup per port-add) */
LIST_FOR_EACH(provider, node, &dpif_offload_providers) {
    if (!strcmp(provider->name, type)) { break; }  /* O(P) */
}

/* After */
/* CWE-407 fix: shash for O(1) provider lookup instead of O(P) LIST_FOR_EACH strcmp scan. */
struct dpif_offload_provider *provider =
    shash_find_data(&dpif_offload_provider_map, type);  /* O(1) */

/* Before — line 229 (dup check per registration) */
LIST_FOR_EACH(existing, node, &dpif_offload_providers) {
    if (!strcmp(existing->name, provider->name)) { return EEXIST; }  /* O(P) */
}

/* After */
/* CWE-407 fix: shash_find for O(1) dup check instead of O(P) list scan. */
if (shash_find(&dpif_offload_provider_map, provider->name)) {
    return EEXIST;  /* O(1) */
}
shash_add(&dpif_offload_provider_map, provider->name, provider);

Patch

defects/ovs/patch/ovs-0001-dpif-offload-provider-shash.patch

What We Ask

Confirm receipt and assign a security advisory reference (openvswitch/ovs).
Validate the patch against the dpif offload test suite.
Assess CVE eligibility — ovs-0001 fires on every port-add event in hardware-offload deployments.
Coordinate a disclosure date — we are targeting 90 days from first contact.

Contact: see cover email. This brief is confidential until coordinated disclosure.

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