zcat: failure to correctly extract files

Denys Vlasenko vda.linux at googlemail.com
Sun Jun 15 21:47:53 UTC 2014


On Friday 13 June 2014 11:28, Jack Mitchell wrote:
> I have recently upgraded to busybox v1.18.3 to v1.22.1 and seem to have
> discovered a bug in zcat.
> 
> I'm not entirely sure what the problem is, but files don't seem to be
> extracted correctly. The following procedure creates a basic filesytem
> image, gzips it on the host then scp's it to the target where zcat fails
> to properly extract it, while gunzip -c succeeds. It's very similar to
> my use-case and shows the issue.
> 
> On the host:
> 
> [jack at jackArch busybox-test]$ dd if=/dev/zero of=test.img bs=1MB count=100
> 100+0 records in
> 100+0 records out
> 100000000 bytes (100 MB) copied, 0.157787 s, 634 MB/s
> 
> [jack at jackArch busybox-test]$ mkfs.ext3 test.img
> mke2fs 1.42.9 (28-Dec-2013)
> Allocating group tables: done
> Writing inode tables: done
> Creating journal (4096 blocks): done
> Writing superblocks and filesystem accounting information: done
> 
> [jack at jackArch busybox-test]$ sudo mount test.img /mnt/tmp
> [sudo] password for jack:
> 
> [jack at jackArch busybox-test]$ ls -la /mnt/tmp
> total 17
> drwxr-xr-x  3 root root  1024 Jun 12 17:14 .
> drwxr-xr-x 10 root root  4096 Jun  9 13:18 ..
> drwx------  2 root root 12288 Jun 12 17:14 lost+found
> 
> [jack at jackArch busybox-test]$ sudo umount /mnt/tmp
> 
> [jack at jackArch busybox-test]$ dd if=test.img bs=1k | gzip -v9 > test-zcat
> 97656+1 records in
> 97656+1 records out
> 100000000 bytes (100 MB) copied, 0.574901 s, 174 MB/s
>  99.9%
> 
> [jack at jackArch busybox-test]$ scp test-zcat root at 192.168.0.254:/mnt/persist
> test-zcat
> 100%  108KB 108.5KB/s   00:00
> 
> 
> On the target:
> 
> target# pwd
> /mnt/persist
> 
> target# ls -lah test-zcat
> -rw-r--r--    1 root     root      108.5K Jun 13 09:19 test-zcat
> 
> target# time zcat test-zcat > test.img
> real	0m 0.00s
> user	0m 0.00s
> sys	0m 0.00s
> 
> target# ls -lah test.img
> -rw-r--r--    1 root     root      108.5K Jun 13 09:20 test.img
> 
> target# mount test.img /mnt/tmp/
> mount: wrong fs type, bad option, bad superblock on /dev/loop4,
>        missing codepage or helper program, or other error
> 
>        In some cases useful info is found in syslog - try
>        dmesg | tail or so.
> 
> target# time gunzip -c test-zcat > test2.img
> real	0m 1.90s
> user	0m 1.31s
> sys	0m 0.58s
> 
> target# ls -lah test2.img
> -rw-r--r--    1 root     root       95.4M Jun 13 09:21 test2.img
> 
> target# mount test2.img /mnt/tmp/
> 
> target# ls -la /mnt/tmp/
> drwxr-xr-x    3 root     root          1024 Jun 12 16:14 .
> drwxr-xr-x    9 root     root          4096 Jun 12 16:32 ..
> drwx------    2 root     root         12288 Jun 12 16:14 lost+found
> 
> If you have any questions please let me know and I'll do my best to help.


Please try current git. I remember there was a fix for this.


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