zcat: failure to correctly extract files

[Jack Mitchell]

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.

Regards,
Jack

-- 
  Jack Mitchell (jack at embed.me.uk)
  Embedded Systems Engineer
  Cambridgeshire, UK
  http://www.embed.me.uk
--