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/* simple program to check implanted md5sum in an iso 9660 image */
/* Copyright 2001 Red Hat, Inc. */
/* Michael Fulbright msf@redhat.com */
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "md5.h"
/* number of sectors to ignore at end of iso when computing sum */
#define SKIPSECTORS 150
#define APPDATA_OFFSET 883
#define SIZE_OFFSET 84
#define MAX(x, y) ((x > y) ? x : y)
#define MIN(x, y) ((x < y) ? x : y)
/* finds primary volume descriptor and returns info from it */
/* mediasum must be a preallocated buffer at least 33 bytes long */
int parsepvd(int isofd, char *mediasum, long long *isosize) {
unsigned char buf[2048];
long long offset;
unsigned char *p;
if (lseek(isofd, (off_t)(16L * 2048L), SEEK_SET) == -1)
return ((long long)-1);
offset = (16L * 2048L);
for (;1;) {
read(isofd, buf, 2048);
if (buf[0] == 1)
/* found primary volume descriptor */
break;
else if (buf[0] == 255)
/* hit end and didn't find primary volume descriptor */
return ((long long)-1);
offset += 2048L;
}
/* read out md5sum */
memcpy(mediasum, buf + APPDATA_OFFSET + 13, 32);
mediasum[32] = '\0';
for (p=mediasum; *p; p++)
if (*p != ' ')
break;
/* if the md5sum was all spaces, we didn't find md5sum */
if (!*p)
return -1;
/* get isosize */
*isosize = (buf[SIZE_OFFSET]*0x1000000+buf[SIZE_OFFSET+1]*0x10000 +
buf[SIZE_OFFSET+2]*0x100 + buf[SIZE_OFFSET+3]) * 2048LL;
return offset;
}
/* returns -1 if no checksum encoded in media, 0 if no match, 1 if match */
/* mediasum is the sum encoded in media, computedsum is one we compute */
/* both strings must be pre-allocated at least 33 chars in length */
int checkmd5sum(int isofd, char *mediasum, char *computedsum) {
int nread;
int i;
int appdata_start_offset, appdata_end_offset;
int nattempt;
unsigned int bufsize = 32768;
unsigned char md5sum[16];
unsigned int len;
unsigned char *buf;
unsigned long tally_inc, tally;
long long isosize, offset, pvd_offset, apoff;
MD5_CTX md5ctx;
if ((pvd_offset = parsepvd(isofd, mediasum, &isosize)) < 0)
return -1;
/* printf("Mediasum = %s\n",mediasum); */
/* rewind, compute md5sum */
lseek(isofd, 0L, SEEK_SET);
MD5_Init(&md5ctx);
offset = 0;
apoff = pvd_offset + APPDATA_OFFSET;
buf = malloc(bufsize * sizeof(unsigned char));
tally_inc = 50*1000*1000;
tally = 0;
while (offset < isosize - SKIPSECTORS*2048) {
nattempt = MIN(isosize - SKIPSECTORS*2048 - offset, bufsize);
/* printf("%lld %lld %lld %d\n", offset, isosize, isosize-SKIPSECTORS*2048, nattempt); */
nread = read(isofd, buf, nattempt);
if (nread <= 0)
break;
/* overwrite md5sum we implanted with original data */
if (offset < apoff && offset+nread >= apoff) {
appdata_start_offset = apoff - offset;
appdata_end_offset = MIN(appdata_start_offset+MIN(nread, 512),
offset + nread - apoff);
len = appdata_end_offset - appdata_start_offset;
memset(buf+appdata_start_offset, ' ', len);
} else if (offset >= apoff && offset+nread < apoff + 512) {
appdata_start_offset = 0;
appdata_end_offset = nread;
len = appdata_end_offset - appdata_start_offset;
memset(buf+appdata_start_offset, ' ', len);
} else if (offset < apoff + 512 && offset+nread >= apoff + 512) {
appdata_start_offset = 0;
appdata_end_offset = apoff + 512 - offset;
len = appdata_end_offset - appdata_start_offset;
memset(buf+appdata_start_offset, ' ', len);
}
MD5_Update(&md5ctx, buf, nread);
offset = offset + nread;
if (offset >= tally) {
printf("Read %5d MB\n", tally/1000/1000);
tally += tally_inc;
}
}
sleep(1);
free(buf);
MD5_Final(md5sum, &md5ctx);
*computedsum = '\0';
for (i=0; i<16; i++) {
char tmpstr[4];
snprintf (tmpstr, 4, "%02x", md5sum[i]);
strcat(computedsum, tmpstr);
}
/* printf("mediasum, computedsum = %s %s\n", mediasum, computedsum); */
if (strcmp(mediasum, computedsum))
return 0;
else
return 1;
}
int main(int argc, char **argv) {
int isofd;
int rc;
unsigned char mediasum[33], computedsum[33];
if (argc < 2) {
printf("Usage: checkisomd5 <isofilename>\n\n");
exit(1);
}
isofd = open(argv[1], O_RDONLY);
if (isofd < 0) {
fprintf(stderr, "Error - Unable to open file %s\n\n", argv[1]);
exit(1);
}
rc = checkmd5sum(isofd, mediasum, computedsum);
printf("%s\n%s\n", mediasum, computedsum);
if ( rc == 0)
printf("Md5sums differ.\n");
else if (rc > 0)
printf("Md5sums match.\n");
else
printf("No checksum information in iso, check skipped.\n");
close(isofd);
}
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