Last month I posted a portion of a ridiculous conversation with NETGEAR over source code it withheld to unpack the filesystem on one of its routers.  I would like to announce that against all expectations, NETGEAR actually pulled through and sent me the source code I was looking for!

As mentioned previously, I posted a detailed explanation of my situation over on the OpenWRT forum.  To avoid any unnecessary re-explaining of background information, I’ll copy/paste it here:

---

Hey guys,

I’m trying to unpack SquashFS on the WNR1000v3 1.0.2.26 but have been running into lots of issues.

The firmware image is available here: http://www.downloads.netgear.com/files/WNR1000v3-V1.0.2.26_51.0.59NA.chk

The source for it is available here: http://www.downloads.netgear.com/files/GPL/WNR1000v3-V1.0.2.26_51.0.59NAWW_src.tar.zip

binwalk 0.4.2 provides the following output:

DECIMAL   	HEX       	DESCRIPTION
-------------------------------------------------------------------------------------------------------
58        	0x3A      	TRX firmware header, little endian, header size: 28 bytes,  image size: 2584576 bytes, CRC32: 0x9861D9FF flags/version: 0x10000
86        	0x56      	LZMA compressed data, properties: 0x5D, dictionary size: 65536 bytes, uncompressed size: 1634304 bytes
592666    	0x90B1A   	Squashfs filesystem, little endian, non-standard signature,  version 3.0, size: 1988809 bytes, 421 inodes, blocksize: 65536 bytes, created: Fri Jul 16 06:30:19 2010

Extract the filesystem at offset 592666:

$ dd if=WNR1000v3-V1.0.2.26_51.0.59NA.chk of=filesystem.bin bs=592666 skip=1
3+1 records in
3+1 records out
1991968 bytes (2.0 MB) copied, 0.0391462 s, 50.9 MB/s

As noted by binwalk, the filesystem has a non-standard magic number:

$ hexdump -C filesystem.bin | head -n2
00000000  73 68 73 71 a5 01 00 00  84 7a 00 37 dc 7c 00 de  |shsq.....z.7.|..|
00000010  8a 04 08 40 06 01 40 02  00 63 00 09 03 00 00 00  |...@..@..c......|

Trying to unpackage it immediately returns the following error:

$ unsquashfs filesystem.bin
Can't find a SQUASHFS superblock on filesystem.bin

…which is to be expected. Correct the magic number to “hsqs” and now:

$ unsquashfs filesystem.bin
Parallel unsquashfs: Using 2 processors
gzip uncompress failed with error code -3
read_block: failed to read block @0x1e547f
read_fragment_table: failed to read fragment table block
FATAL ERROR aborting: failed to read fragment table

A little sleuthing returns that the filesystem is actually compressed using lzma, not gzip, so try a different compilation:

$ ../../../firmware-mod-kit-read-only/trunk/src/others/squashfs-4.0-lzma/unsquashfs-lzma filesystem.bin
Parallel unsquashfs: Using 2 processors
uncompress failed, unknown error -3
read_block: failed to read block @0x1e547f
read_fragment_table: failed to read fragment table block
FATAL ERROR aborting: failed to read fragment table

I can confirm that none of the publicly available unsquashfs utilities I can find are able to unpackage the file. I’ve tried using every version of unsquashfs, every variant of it, in every package that incorporates it (e.g., firmware-mod-kit). firmware-mod-kit’s scripts are unsuccessful as well.

Looking through the firmware source code, I see:

$ find . -name *squash*
./src/router/mipsel-uclibc/target.squashfs
./src/router/squashfs
./src/router/squashfs/mksquashfs.c
./src/router/squashfs/mksquashfs.h
./src/linux/linux/scripts/squashfs
./src/linux/linux/scripts/squashfs/mksquashfs
./src/linux/linux/scripts/squashfs/mksquashfs.c
./src/linux/linux/scripts/squashfs/mksquashfs.h
./src/linux/linux/scripts/squashfs/squashfs_fs.h
./src/linux/linux/fs/squashfs
./src/linux/linux/fs/squashfs/.squashfs2_0.o.flags
./src/linux/linux/fs/squashfs/squashfs2_0.o
./src/linux/linux/fs/squashfs/squashfs.o
./src/linux/linux/fs/squashfs/squashfs.h
./src/linux/linux/fs/squashfs/squashfs2_0.c
./src/linux/linux/fs/squashfs/.squashfs.o.flags
./src/linux/linux/include/linux/squashfs_fs_i.h
./src/linux/linux/include/linux/squashfs_fs.h
./src/linux/linux/include/linux/squashfs_fs_sb.h
./src/linux/linux/include/config/squashfs.h
./src/linux/linux/include/config/squashfs

…and unfortunately no unsquashfs.c code. In the meantime, I’ve contacted Netgear asking if they have it available.

The exact version they’re using is a bit confusing:

$ grep "mksquashfs version" -r .
./src/router/mipsel-uclibc/target/lib/modules/2.4.20/build/scripts/squashfs/mksquashfs.c:	printf("mksquashfs version 2.2-r2n");
./src/router/squashfs/mksquashfs.c:	printf("mksquashfs version 3.2-r2 (2007/01/15)n");
./src/linux/linux/scripts/squashfs/mksquashfs.c:	printf("mksquashfs version 2.2-r2n");

Grepping for our non-standard magic number reveals:

$ grep 0x73687371 -r .
./src/router/mipsel-uclibc/target/lib/modules/2.4.20/build/include/linux/squashfs_fs.h:#define SQUASHFS_MAGIC_LZMA_SWAP	0x73687371
./src/linux/linux/include/linux/squashfs_fs.h:#define SQUASHFS_MAGIC_LZMA_SWAP	0x73687371

Okay, great. Some Googling and it seems that this patch should do the trick: https://dev.openwrt.org/browser/trunk/tools/squashfs4/patches/170-add_support_for_LZMA_MAGIC_to_unsqashfs.patch?rev=28489
Patch unsquashfs, rebuild, and:

$ ./unsquashfs ../../filesystem.bin
Parallel unsquashfs: Using 2 processors
lzma uncompress failed with error code 1
read_block: failed to read block @0x1e547f
read_fragment_table: failed to read fragment table block
FATAL ERROR aborting: failed to read fragment table

Would anyone have any advice to offer, or mind lending a hand trying to get this filesystem unpackaged? Thank you in advance.

---

After about a month of back and forth conversation with their technical support team, I finally received a message linking me to the unsquashfs.c file I was looking for (download link is at the end of this post).

The following steps outline how to compile:

1. Download and extract http://www.downloads.netgear.com/files/GPL/WNR1000v3-V1.0.2.26_51.0.59NAWW_src.tar.zip
2. Copy unsquashfs.c into bcm5356/src/router/squashfs
3. `cd bcm5356/src/router/squashfs; make`

sh-4.1$ ./unsquashfs
SYNTAX: ./unsquashfs [options] filesystem [directory or file to extract]
	-v[ersion]		print version, licence and copyright information
	-i[nfo]			print files as they are unsquashed
	-l[s]			list filesystem only
	-d[est] 	unsquash to , default "squashfs-root"
	-f[orce]		if file already exists then overwrite
sh-4.1$ ./unsquashfs -version
unsquashfs version 1.3 (2007/01/02)
copyright (C) 2007 Phillip Lougher 

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2,
or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
sh-4.1$

And to demonstrate its functionality:

sh-4.1$ dd if=WNR1000v3-V1.0.2.26_51.0.59NA.chk of=filesystem.bin bs=592666 skip=1
3+1 records in
3+1 records out
1991968 bytes (2.0 MB) copied, 0.0060848 s, 327 MB/s
sh-4.1$ ./unsquashfs filesystem.bin 

created 327 files
created 35 directories
created 59 symlinks
created 0 devices
created 0 fifos
sh-4.1$ ls -R squashfs-root/
squashfs-root/:
bin  dev  etc  lib  media  mnt	proc  sbin  sys  tmp  usr  var	www

squashfs-root/bin:
busybox  cp    gunzip  ls     mount  ps   rmdir   wps_ap
cat	 eapd  gzip    mkdir  msh    pwd  sh	  wps_monitor
chmod	 echo  kill    mknod  ping   rm   umount  zcat

squashfs-root/dev:

squashfs-root/etc:
icon.ico  large.ico    ld.so.conf  ppp		small.ico
iproute2  ld.so.cache  lld2d.conf  resolv.conf

squashfs-root/etc/iproute2:

squashfs-root/etc/ppp:

squashfs-root/lib:
ld-uClibc.so.0	libc.so.0   libgcc_s.so.1  libpthread.so.0  libutil.so.0
libcrypt.so.0	libdl.so.0  libm.so.0	   libresolv.so.0   modules

squashfs-root/lib/modules:
2.4.20

squashfs-root/lib/modules/2.4.20:
build  kernel  pcmcia

squashfs-root/lib/modules/2.4.20/kernel:
drivers  net

squashfs-root/lib/modules/2.4.20/kernel/drivers:
net

squashfs-root/lib/modules/2.4.20/kernel/drivers/net:
emf  et  igs  wl

squashfs-root/lib/modules/2.4.20/kernel/drivers/net/emf:
emf.o

squashfs-root/lib/modules/2.4.20/kernel/drivers/net/et:
et.o

squashfs-root/lib/modules/2.4.20/kernel/drivers/net/igs:
igs.o

squashfs-root/lib/modules/2.4.20/kernel/drivers/net/wl:
wl.o

squashfs-root/lib/modules/2.4.20/kernel/net:
ipv4

squashfs-root/lib/modules/2.4.20/kernel/net/ipv4:
acos_nat  l7_filter  multissidcontrol  opendns	ubd

squashfs-root/lib/modules/2.4.20/kernel/net/ipv4/acos_nat:
acos_nat.o

squashfs-root/lib/modules/2.4.20/kernel/net/ipv4/l7_filter:
l7_filter.o

squashfs-root/lib/modules/2.4.20/kernel/net/ipv4/multissidcontrol:
MultiSsidControl.o

squashfs-root/lib/modules/2.4.20/kernel/net/ipv4/opendns:
openDNS_hijack.o

squashfs-root/lib/modules/2.4.20/kernel/net/ipv4/ubd:
ubd.o

squashfs-root/lib/modules/2.4.20/pcmcia:

squashfs-root/mnt:

squashfs-root/proc:

squashfs-root/sbin:
acos_init     burnrf	 ifconfig  ntpclient  reset_no_reboot	     version
acos_service  burnsn	 init	   pppd       restart_all_processes  write
bd	      erase	 insmod    preinit    rmmod
burnboardid   getchksum  leddown   rc	      routerinfo
burnethermac  gpio	 ledup	   read_bd    ubdcmd
burnpin       hotplug	 lsmod	   reboot     uptime

squashfs-root/sys:

squashfs-root/tmp:

squashfs-root/usr:
bin  lib  sbin	tmp

squashfs-root/usr/bin:
free  killall  route  telnetd  tftp  wget

squashfs-root/usr/lib:
libacos_shared.so  libbcm.so  libnvram.so   libwpscom.so
libbcmcrypto.so    libnat.so  libshared.so  tc

squashfs-root/usr/lib/tc:
q_netem.so

squashfs-root/usr/sbin:
acl_logd	   email      lld2d	   swresetd	  upnpd        wlconf
bpalogin	   emf	      nas	   tc		  upnpnat      wpsd
bpa_monitor	   epi_ttcp   nvram	   telnetenabled  vconfig      zebra
brctl		   et	      outputimage  tfmeter	  wan_debug
cli		   ftpc       pot	   timesync	  wandetect
ddnsd		   heartbeat  pppoecd	   udhcpc	  wanled
dnsmasq		   httpd      pptp	   udhcpd	  wl
dnsRedirectReplyd  igs	      ripd	   upnp		  wlanconfigd

squashfs-root/www:
Add_WPS_Client.htm		 PWD_password.htm
backpage2.htm			 QOS_check_uplink_band_width.htm
backpage.htm			 QOS_main_h.htm
BAK_backup_h.htm		 QOS_main.htm
BAK_backup.htm			 QOS_ruletab.htm
BAK_cfm.htm			 QOS_service.htm
BAS_basic.htm			 redbull.gif
BAS_basictop.htm		 router-info.htm
BAS_bpa_h.htm			 RST_interval.htm
BAS_bpa.htm			 RST_statistics.htm
BAS_ether_h.htm			 RST_stattbl.htm
BAS_ether.htm			 RST_status_h.htm
BAS_pppoe_basic.htm		 RST_status.htm
BAS_pppoe_basictop.htm		 RST_st_bpa.htm
BAS_pppoe_flet2.htm		 RST_st_dhcp.htm
BAS_pppoe_flet.htm		 RST_st_fix.htm
BAS_pppoe_h.htm			 RST_st_poe.htm
BAS_pppoe.htm			 RST_st_pptp.htm
BAS_pppoe_other.htm		 RST_wanstat.htm
BAS_pptp_h.htm			 settings_wnr1000v3.jpg
BAS_pptp.htm			 spacer.gif
BAS_wtest_d.htm			 SRV_response.htm
BAS_wtest_l.htm			 start.htm
BAS_wtest_ppp2.htm		 start_update.htm
BKS_err.htm			 STR_add.htm
BKS_keyword_h.htm		 StringTableUpload.html
BKS_keyword.htm			 string_table_wnr1000v3
BKS_keyword_ppp2.htm		 STR_routes_h.htm
BKS_service_add_h.htm		 STR_routes.htm
BKS_service_add.htm		 style.css
BKS_service_edit.htm		 traffic_important_update.htm
BKS_service_h.htm		 traffic_interval.htm
BKS_service.htm			 traffic_meter_h.htm
BKS_service_ppp2.htm		 traffic_meter.htm
browser.js			 traffic_start_update.htm
CheckNewFW.html			 traffic_stattbl.htm
currentsetting.htm		 traffic_status.htm
darkblue.gif			 traffic_warning.htm
debuginfo.htm			 UPG_fw_check.htm
DEV_device_h.htm		 UPG_upgrade_h.htm
DEV_device.htm			 UPG_upgrade.htm
DIG_reboot2.htm			 upload.gif
DIG_reboot3.htm			 UPNP_upnp_h.htm
DIG_reboot4.htm			 UPNP_upnp.htm
DIG_reboot.htm			 utility.js
DIG_update.htm			 VER_check_h.htm
DNS_ddns_h.htm			 VER_check.htm
DNS_ddns.htm			 VER_download_h.htm
DNS_ddns_st.htm			 VER_download.htm
form.css			 VER_fw_found.htm
func.js				 VER_fwlang_found.htm
FW_check.htm			 VER_fw_not_found.htm
FW_email_h.htm			 VER_result_h.htm
FW_email.htm			 VER_sel_h.htm
FW_forward_h.htm		 VER_sel.htm
FW_forward.htm			 VER_write2.htm
FW_forward_service_h.htm	 VER_write_h.htm
FW_forward_service.htm		 VER_write.htm
FW_log_h.htm			 WAN_wan_h.htm
FW_log.htm			 WAN_wan.htm
FW_pt_h.htm			 WiFi_HiddenPage.htm
FW_pt.htm			 WIZ_bpa_h.htm
FW_pt_service.htm		 WIZ_bpa.htm
FW_remote_h.htm			 WIZ_cfm_h.htm
FW_remote.htm			 WIZ_cfm.htm
FW_schedule_h.htm		 WIZ_det_fix_h.htm
FW_schedule.htm			 WIZ_det_fix.htm
FW_schedule_ppp2.htm		 WIZ_detwan.htm
help.css			 WIZ_dyn_h.htm
IA_IP_SUBNET.htm		 WIZ_dyn.htm
important_update.htm		 WIZ_fix_h.htm
index.htm			 WIZ_fix.htm
LANG_brs_conflict_h.htm		 WIZ_ph_fail_h.htm
LANG_brs_conflict.htm		 WIZ_ph_fail.htm
LANG_check_brslang.htm		 WIZ_pppoe_fleteast.htm
LANG_check.htm			 WIZ_pppoe_fletother.htm
LANG_check_top.htm		 WIZ_pppoe_fletwest.htm
LANG_download.htm		 WIZ_pppoe_h.htm
LANG_failed.htm			 WIZ_pppoe.htm
LANG_found.htm			 WIZ_pptp_h.htm
LANG_lang_h.htm			 WIZ_pptp.htm
LANG_lang.htm			 WIZ_result.htm
LANG_no_connection.htm		 WIZ_sel_h.htm
LANG_not_found.htm		 WIZ_sel.htm
LANG_upgrade.htm		 WLG_acl_add_h.htm
LANG_write.htm			 WLG_acl_add.htm
LAN_lan_h.htm			 WLG_acl_edit.htm
LAN_lan.htm			 WLG_acl_h.htm
LAN_reserv_add_h.htm		 WLG_acl.htm
LAN_reserv_add.htm		 WLG_adv_h.htm
LAN_reserv_edit_h.htm		 WLG_adv.htm
LAN_reserv_edit.htm		 WLG_wds_h.htm
LGO_logout.htm			 WLG_wds.htm
liteblue.gif			 WLG_wireless1_2.htm
md5.js				 WLG_wireless1.htm
menublue.gif			 WLG_wireless2_2.htm
mimo_logo_wnr1000v3.jpg		 WLG_wireless_2_h.htm
MNU_access_failure.htm		 WLG_wireless_2.htm
MNU_access_unauthorized.htm	 WLG_wireless2.htm
MNU_blank.htm			 WLG_wireless3_2.htm
MNU_login.htm			 WLG_wireless3.htm
MNU_menu.htm			 WLG_wireless4_2.htm
MNU_menu_no_link.htm		 WLG_wireless_h.htm
MNU_top.htm			 WLG_wireless.htm
msg.js				 WPS_Add_Client_FAIL_Cancel_Change.htm
NoInternetConn.html		 WPS_Add_Client_FAIL_Cancel.htm
NoInternet.html			 WPS_Add_Client_FAIL_ErrorPIN.htm
POT.htm				 WPS_Add_Client_FAIL_PBC_Conflict_Change.htm
pppoe2_domain_add.htm		 WPS_Add_Client_FAIL_PBC_Conflict.htm
pppoe2_domain_edit.htm		 WPS_Add_Client_FAIL_PIN_Change.htm
pppoe2_ip_add.htm		 WPS_Add_Client_FAIL_PIN.htm
pppoe2_ip_edit.htm		 WPS_Add_Client_FAIL_Timeout_Change.htm
pppoe2_port_add.htm		 WPS_Add_Client_FAIL_Timeout.htm
pppoe2_port_edit.htm		 WPS_Add_Client_OK_Change.htm
Public_UPNP_gatedesc.xml	 WPS_Add_Client_OK.htm
Public_UPNP_LANHostCfgMag.xml	 WPS_Add_Client_PBC.htm
Public_UPNP_Layer3F.xml		 WPS_Add_Client_PIN.htm
Public_UPNP_WAND.xml		 WPS_h.htm
Public_UPNP_WANEtherLinkCfg.xml  WPS.htm
Public_UPNP_WANIPConn.xml	 wps_icon_off.bmp
Public_UPNP_WANPPPConn.xml	 wps_icon_on.bmp
PWD_passwd_h.htm		 WPS_PIN.htm
sh-4.1$

In summary, the following code has been verified to unpack SquashFS filesystems on the following NETGEAR devices:

• WNR1000v3 1.0.26NA
• WGR614v10 1.0.26NA

The unsquashfs code may be downloaded here: unsquashfs-1.3.c

If there is one lesson to be learned from this experience, it’s amazing what you can receive if you are polite and simply choose to ask.