version 1 of D-LINK fw image unpacker.

unpack-dlink.c

/*
 * D-LINK products formware image unpacker tool.
 * Written by dev_zzo for personal research.
 * Use at your own risk.
 */
 
#include <stdio.h>
#include <stdint.h>
#include <endian.h>
#include <malloc.h>

/*
The firmware file consists of multiple variable-length records.
Each record is prefixed with a header and may contain a payload.
Integers in the header are in BE order.
*/

/* Entry header. */
struct header
{
    unsigned char magic[4];
    uint32_t headers_length;
    uint32_t payload_length;
    // MD5 hash, if payload_length > 0
};

int main (int argc, char *argv[])
{
    FILE *fpImage;
    int record_index = 1;
    
    fpImage = fopen (argv[1], "rb");
    if (!fpImage)
    {
        fprintf (stderr, "Failed to open the image file.\n");
        return 1;
    }
    
    for(;;)
    {
        struct header hdr;
        char *headers;
        int i;
        
        fprintf(stdout, "trying to read record #%d...\n", record_index);
        
        if (fread (&hdr, sizeof(hdr), 1, fpImage) < 1)
        {
            if (feof (fpImage))
            {
                fprintf (stderr, "EOF when reading the header, considering this done.\n");
                break;
            }
            fprintf (stderr, "Failed to read the header magic.\n");
            fclose (fpImage);
            return 2;
        }
        
        if (hdr.magic[0] != 0x5EU || hdr.magic[1] != 0xA3U || hdr.magic[2] != 0xA4U || hdr.magic[3] != 0x17U)
        {
            fprintf (stderr, "Header magic is invalid: %02X%02X%02X%02X.\n",
                hdr.magic[0] & 0xFF, hdr.magic[1] & 0xFF, hdr.magic[2] & 0xFF, hdr.magic[3] & 0xFF);
            fclose (fpImage);
            return 2;
        }
        
        hdr.headers_length = be32toh(hdr.headers_length);
        hdr.payload_length = be32toh(hdr.payload_length);
        
        fprintf (stdout, "Headers: %u bytes.\n", hdr.headers_length);
        fprintf (stdout, "Payload: %u bytes.\n", hdr.payload_length);
        
        if (hdr.payload_length != 0)
        {
            char hash[16];
            
            if (fread (hash, 16, 1, fpImage) < 1)
            {
                fprintf (stderr, "Failed to read the payload hash.\n");
                fclose (fpImage);
                return 2;
            }
        
            /* TODO: check the payload hash. */
        }
        
        headers = (char *)calloc (hdr.headers_length + 1, 1);
        if (fread (headers, hdr.headers_length, 1, fpImage) < 1)
        {
            fprintf (stderr, "Failed to read headers data.\n");
            free (headers);
            fclose (fpImage);
            return 2;
        }
        
        for(i = 0; i < hdr.headers_length; ++i)
        {
            if (headers[i] == 0x00)
                headers[i] = '\n';
        }
        
        fprintf (stdout, "%s", headers);
        
        free (headers);
        
        {
            FILE *fpOutput;
            char output_name[256];
            
            sprintf (output_name, "section.%03d", record_index);
            fpOutput = fopen (output_name, "wb");
            
            while (hdr.payload_length != 0)
            {
                char buffer[4096];
                int count = hdr.payload_length > 4096 ? 4096 : hdr.payload_length;
                fread (buffer, count, 1, fpInput);
                fwrite (buffer, count, 1, fpOutput);
                hdr.payload_length -= count;
            }
            
            fclose (fpOutput);
        }
        
        fseek(fpImage, hdr.payload_length, SEEK_CUR);
        
        record_index++;
    }
    
    fclose (fpImage);
    
    return 0;
}