Bug#576520: cdbackup: CRC checks fail on DVD images

[Petter Reinholdtsen]

Control: tags -1 + patch

[Phil Reynolds 2010-04-05]
> When writing virtual images for later burning to DVDs, if the -C switch 
> to cdbackup is not used, the tracks in the images cannot be restored 
> using cdrestore as the CRC check fails. This applies whether the images 
> are on DVD or have been kept on a hard disc.

I wonder, could this be caused by a memory overflow in the CRC
calculating code?  If so, I propose this patch to fix it.

Description: Make sure setting and reading CRC do not work past buffer size.
 The code used to store 8 bytes in a 4 byte space, and read 8 bytes from a 4
 byte space on 64 bit platforms.  Rewrite to use int32_t to ensure only 4
 bytes are used.
Author: Petter Reinholdtsen 
Bug-Debian: https://bugs.debian.org/576520
Forwarded: no
Last-Update: 2024-06-15
---
--- cdbackup-0.7.1.orig/cdbackup.c
+++ cdbackup-0.7.1/cdbackup.c
@@ -29,6 +29,7 @@ SUCH DAMAGE.
 #include 
 #include 
 #include 
+#include 
 #include 
 #include 
 #include 
@@ -392,8 +393,8 @@ int backup(void)
 }
   }
 if(crc) {
-  int l=crc32(buffer,bytes+DBSIZE);
-  *((unsigned long *)([CD_FRAMESIZE-4]))=l;
+  int32_t l=crc32(buffer,bytes+DBSIZE);
+  *((int32_t *)([CD_FRAMESIZE-sizeof(l)]))=l;
   }
 Vwrite(buffer); grandTotal+=CD_FRAMESIZE;
 } while(db->status==0);
--- cdbackup-0.7.1.orig/cdrestore.c
+++ cdbackup-0.7.1/cdrestore.c
@@ -28,6 +28,7 @@ SUCH DAMAGE.
 
 #include 
 #include 
+#include 
 #include 
 #include 
 #include 
@@ -203,8 +204,8 @@ int restore(int disktrack)
   }
 
 if(db->flags_CRC) {
-  int l=crc32(buffer,size+DBSIZE);
-  if(*((unsigned long *)([CD_FRAMESIZE-4]))!=l) {
+  int32_t l=crc32(buffer,size+DBSIZE);
+  if(*((int32_t *)([CD_FRAMESIZE-sizeof(l)]))!=l) {
 if(verbose) fprintf(stderr,"%s: bad CRC checksum at 
%lld\n",prg_name,totalRead);
 serror("Bad checksum, block corrupted, restore failed");
 }

The patch is commited to the git repo on
https://salsa.debian.org/debian/cdbackup >, but not uploaded as I could
like to know if it solve this bug first.  Are you able to test it?

-- 
Happy hacking
Petter Reinholdtsen

Bug#576520: cdbackup: CRC checks fail on DVD images

[Phil Reynolds]

Package: cdbackup
Version: 0.7.0-5
Severity: normal

When writing virtual images for later burning to DVDs, if the -C switch 
to cdbackup is not used, the tracks in the images cannot be restored 
using cdrestore as the CRC check fails. This applies whether the images 
are on DVD or have been kept on a hard disc.

A workaround is to use cdbackup's -C switch which writes images without 
the data necessary for CRC checking. cdrestore restores these without 
problem - I have verified with diff that the restored files match 
the originals, even when the track is split between images.

The lack of CRC checking does mean that some types of error in the data 
cannot be detected, but they would be if it worked.

-- System Information:
Debian Release: 5.0.4
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.26-2-amd64 (SMP w/3 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages cdbackup depends on:
ii  libc6   2.7-18lenny2 GNU C Library: Shared libraries
ii  wodim   9:1.1.9-1command line CD/DVD writing tool

Versions of packages cdbackup recommends:
ii  cpio  2.9-13 GNU cpio -- a program to manage ar

cdbackup suggests no packages.

-- no debconf information



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