insert_edge writes out-of-bounds when vertex index exceeds MAXV

[bushidocodes]

Summary

The insert_edge function in src/sean/wasm/graph.c accesses g->edges[source] and g->degree[source] without first verifying that source (or destination) is within the array bounds. The edges field is declared as edge *edges[MAXV + 1] (70001 elements, valid indices 0–70000). If a JavaScript caller passes a vertex index greater than 70000 via the exported insertEdge(source, destination) WASM API, the function writes past the end of the array, causing undefined behavior or a memory safety violation.

Evidence

Repository: bushidocodes/graph500-web
File(s):

• src/sean/wasm/graph.c:60-79
• src/sean/wasm/constants.h:1

Observed:

• constants.h defines #define MAXV 70000
• graph.c:17 declares edge *edges[MAXV + 1] (indices 0..70000)
• graph.c:62: int32_t max = source > destination ? source : destination;
• graph.c:64: if (max > g->number_vertices) g->number_vertices = max; — updates the vertex count but does not bounds-check against MAXV
• graph.c:76: new_edge->next = g->edges[source]; — unchecked array access
• graph.c:78: g->edges[source] = new_edge; — unchecked array write
• graph.c:79: g->degree[source]++; — unchecked array write
• src/sean/wasm/main.c exports insertEdge(int32_t source, int32_t destination) which forwards directly to insert_edge without any validation

Why this matters

This is a WASM module compiled with Emscripten and called from JavaScript. There is no language-level safety barrier preventing a JavaScript caller from passing arbitrarily large vertex indices. An out-of-bounds write corrupts the linear memory heap, which in WASM means adjacent allocations (including other graph state) can be silently overwritten, producing wrong BFS results or crashing the WASM instance.

Suggested fix

Add a bounds check at the top of insert_edge before any array access:

if (source <= 0 || source > MAXV || destination <= 0 || destination > MAXV) {
    fprintf(stderr, "insert_edge: vertex out of range [1, %d]: source=%d dest=%d\n",
            MAXV, source, destination);
    return;
}

Apply the same check inside insertEdge in main.c so the public API validates inputs before forwarding them.