AVI file reader for SECCON 2019 Online CTF

reader.c

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

char buf[1024 * 1024 * 4];

typedef struct _avimainheader {
  uint32_t fcc;
  uint32_t cb;
  uint32_t dwMicroSecPerFrame;
  uint32_t dwMaxBytesPerSec;
  uint32_t dwPaddingGranularity;
  uint32_t dwFlags;
  uint32_t dwTotalFrames;
  uint32_t dwInitialFrames;
  uint32_t dwStreams;
  uint32_t dwSuggestedBufferSize;
  uint32_t dwWidth;
  uint32_t dwHeight;
  uint32_t dwReserved[4];
} AVIMAINHEADER;

typedef struct {
  uint32_t ckid;
  uint32_t dwFlags;
  uint32_t dwChunkOffset;
  uint32_t dwChunkLength;
} AVIINDEXENTRY;

typedef struct {
  uint32_t CompressedBMHeight;
  uint32_t CompressedBMWidth;
  uint32_t ValidBMHeight;
  uint32_t ValidBMWidth;
  uint32_t ValidBMXOffset;
  uint32_t ValidBMYOffset;
  uint32_t VideoXOffsetInT;
  uint32_t VideoYValidStartLine;
} VIDEO_FIELD_DESC;

typedef struct {
  uint32_t VideoFormatToken;
  uint32_t VideoStandard;
  uint32_t dwVerticalRefreshRate;
  uint32_t dwHTotalInT;
  uint32_t dwVTotalInLines;
  uint32_t dwFrameAspectRatio;
  uint32_t dwFrameWidthInPixels;
  uint32_t dwFrameHeightInLines;
  uint32_t nbFieldPerFrame;
  VIDEO_FIELD_DESC FieldInfo[];
} VideoPropHeader;

void pad(int depth) {
  for (int i = 0; i < depth * 2; i++) putchar(' ');
}

void parse(int idx, int chunk_size, int depth) {
  int i = idx;
  while (i < chunk_size) {
    i = (i + 1) & ~1;
    pad(depth);
    printf("@+0x%06X: %.4s\n", i, &buf[i]);
    int size = *(uint32_t *)&buf[i + 4];
    pad(depth);
    printf("  size = %d\n", size);
    if (strncmp(&buf[i], "avih", 4) == 0) {
      AVIMAINHEADER *avih = (AVIMAINHEADER *)&buf[i];
      pad(depth);
      printf("  dwFlags=0x%X\n", avih->dwFlags);
      pad(depth);
      printf("  dwTotalFrames=%d\n", avih->dwTotalFrames);
      pad(depth);
      printf("  w=%d\n", avih->dwWidth);
      pad(depth);
      printf("  h=%d\n", avih->dwHeight);
    }
    if (strncmp(&buf[i], "LIST", 4) == 0) {
      pad(depth);
      printf("  %.4s\n", &buf[i + 8]);
      parse(i + 12, size - 4, depth + 1);
    }
    if (strncmp(&buf[i], "RIFF", 4) == 0) {
      pad(depth);
      printf("  %.4s\n", &buf[i + 8]);
      parse(i + 12, size - 4, depth + 1);
    }
    if (strncmp(&buf[i], "vprp", 4) == 0) {
      VideoPropHeader *e = (VideoPropHeader *)&buf[i + 8];
      pad(depth);
      printf("  VideoFormatToken: 0x%08X\n", e->VideoFormatToken);
      printf("  VideoStandard: 0x%08X\n", e->VideoStandard);
      printf("  dwVerticalRefreshRate: 0x%08X\n", e->dwVerticalRefreshRate);
      printf("  dwHTotalInT: 0x%08X\n", e->dwHTotalInT);
      printf("  dwVTotalInLines: 0x%08X\n", e->dwVTotalInLines);
      printf("  dwFrameAspectRatio: 0x%08X\n", e->dwFrameAspectRatio);
      printf("  dwFrameHeightInLines: 0x%08X\n", e->dwFrameHeightInLines);
      printf("  nbFieldPerFrame: 0x%08X\n", e->nbFieldPerFrame);
    }
    if (strncmp(&buf[i], "00dc", 4) == 0) {
      pad(depth);
      int k = 0;
      for (; k < 8; k++) {
        printf(" %02X", (uint8_t)buf[i + 8 + k]);
      }
      for (; k < size; k++) {
        if (k % 32 == 8) {
          putchar('\n');
          pad(depth);
        }
        printf(" %02X", (uint8_t)buf[i + 8 + k]);
      }
      putchar('\n');
    }
    if (strncmp(&buf[i], "idx1", 4) == 0) {
      AVIINDEXENTRY *e = (AVIINDEXENTRY *)&buf[i + 8];
      for (int k = 0; k < size / sizeof(AVIINDEXENTRY); k++) {
        pad(depth);
        printf("  %3d: (%8X) +0x%8X %8d\n", k, e[k].dwFlags, e[k].dwChunkOffset,
               e[k].dwChunkLength);
      }
    }
    i += 8 + size;
  }
}

int main(int argc, char *argv[]) {
  FILE *fp = fopen(argv[1], "rb");
  if (!fp) return 1;
  int file_size = fread(buf, 1, sizeof(buf), fp);
  printf("file size: %d\n", file_size);
  int i = 0;
  while (buf[i] == 0) i++;
  parse(i, file_size - i, 0);
  return 0;
}